Other notes

Discussion in 'Python' started by bearophileHUGS@lycos.com, Dec 29, 2004.

  1. Guest

    Here are some questions and suggestions of mine that I've collected in
    the last weeks on the language (please note that some (most?) of them
    are probably wrong/useless/silly, but I've seen that such notes help me
    understand a lot of things and to find my weak spots.)

    1) I've seen that list pop/append is amortised to its tail, but not for
    its head. For this there is deque. But I think dynamical arrays can be
    made with some buffer at both head and tail (but you need to keep an
    index S to skip the head buffer and you have to use this index every
    access to the elements of the list). I think that the most important
    design goal in Python built-in data types is flexibility (and safety),
    instead of just speed (but dictionaries are speedy ^_^), so why there
    are deques instead of lists with both amortised tail&tail operations?
    (My hypothesis: to keep list implementation a bit simpler, to avoid
    wasting memory for the head buffer, and to keep them a little faster,
    avoiding the use of the skip index S).


    2) I usually prefer explicit verbose syntax, instead of cryptic symbols
    (like decorator syntax), but I like the infix Pascal syntax ".." to
    specify a closed interval (a tuple?) of integers or letters (this
    syntax doesn't mean to deprecate the range function). It reminds me the
    .... syntax sometimes used in mathematics to define a sequence.
    Examples:

    assert 1..9 == tuple(range(1,10))
    for i in 1..12: pass
    for c in "a".."z": pass


    3) I think it can be useful a way to define infix functions, like this
    imaginary decorator syntax:

    @infix
    def interval(x, y): return range(x, y+1) # 2 parameters needed

    This may allow:
    assert 5 interval 9 == interval(5,9)


    4) The printf-style formatting is powerful, but I still think it's
    quite complex for usual purposes, and I usually have to look its syntax
    in the docs. I think the Pascal syntax is nice and simpler to remember
    (especially for someone with a little Pascal/Delphi experience ^_^), it
    uses two ":" to format the floating point numbers (the second :number
    is optional). For example this Delphi program:

    {$APPTYPE CONSOLE}
    const a = -12345.67890;
    begin
    writeln(a);
    writeln(a:2:0);
    writeln(a:4:2);
    writeln(a:4:20);
    writeln(a:12:2);
    end.

    Gives:
    -1.23456789000000E+0004
    -12346
    -12345.68
    -12345.67890000000000000000
    -12345.68
    (The last line starts with 3 spaces)


    5) From the docs about round:
    Values are rounded to the closest multiple of 10 to the power minus n;
    if two multiples are equally close, rounding is done away from 0 (so.
    for example, round(0.5) is 1.0 and round(-0.5) is -1.0).
    Example:
    a = [0.05 + x/10.0 for x in range(10)]
    b str(round(x, 1))
    for x in a: print x,
    print
    for x in a: print str(round(x, 1)) + " ",

    Gives:
    0.05 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.85 0.95
    0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

    But to avoid a bias toward rounding up there is another way do this:
    If the digit immediately to the right of the last sig. fig. is more
    than 5, you round up.
    If the digit immediately to the right of the last sig. fig. is less
    than 5, you round down.
    If the digit immediately to the right of the last sig. fig. is equal to
    5, you round up if the last sig. fig. is odd. You round down if the
    last sig. fig. is even. You round up if 5 is followed by nonzero
    digits, regardless of whether the last sig. fig. is odd or even.
    http://www.towson.edu/~ladon/roundo~1.html
    http://mathforum.org/library/drmath/view/58972.html
    http://mathforum.org/library/drmath/view/58961.html


    6) map( function, list, ...) applies function to every item of list and
    return a list of the results. If list is a nested data structure, map
    applies function to just the upper level objects.
    In Mathematica there is another parameter to specify the "level" of the
    apply.

    So:
    map(str, [[1,[2]], 3])
    ==>
    ['[1, [2]]', '3']

    With a hypothetical level (default level = 1, it gives the normal
    Python map):

    map(str, [[1,[2]], 3], level=1)
    ==>
    ['[1, [2]]', '3']

    map(str, [[1,[2]], 3], level=2)
    ==>
    ['1', '[2]', '3']

    I think this semantic can be extended:
    level=0 means that the map is performed up to the leaves (0 means
    infinitum, this isn't nice, but it can be useful because I think Python
    doesn't contain a built-in Infinite).
    level=-1 means that the map is performed to the level just before the
    leaves.
    Level=-n means that the map is performed n levels before the leaves.


    7) Maybe it can be useful to extended the reload(module) semantic:
    reload(module [, recurse=False])
    If recurse=True it reloads the module and recursively all the modules
    that it imports.


    8) Why reload is a function and import is a statement? (So why isn't
    reload a statement too, or both functions?)


    9) Functions without a return statement return None:
    def foo(x): print x
    I think the compiler/interpreter can give a "compilation warning" where
    such function results are assigned to something:
    y = foo(x)
    (I know that some of such cases cannot be spotted at compilation time,
    but the other cases can be useful too).
    I don't know if PyChecker does this already. Generally speaking I'd
    like to see some of those checks built into the normal interpreter.
    Instructions like:
    open = "hello"
    Are legal, but maybe a "compilation warning" can be useful here too
    (and maybe even a runtime warning if a Verbose flag is set).


    10) There can be something in the middle between the def statement and
    the lambda. For example it can be called "fun" (or it can be called
    "def" still). With it maybe both def and lambdas aren't necessary
    anymore. Examples:
    cube = fun x:
    return x**3
    (the last line is indented)

    sorted(data, fun x,y: return x-y)
    (Probably now it's almost impossible to modify this in the language.)


    11) This is just a wild idea for an alternative syntax to specify a
    global variable inside a function. From:

    def foo(x):
    global y
    y = y + 2
    (the last two lines are indented)

    To:

    def foo(x): global.y = global.y + 2

    Beside the global.y, maybe it can exist a syntax like upper.y or
    caller.y that means the name y in the upper context. upper.upper.y etc.


    12) Mathematica's interactive IDE suggests possible spelling errors;
    this feature is often useful, works with builtin name functions too,
    and it can be switched off.
    In[1]:= sin2 = N[Sin[2]]
    Out[1]= 0.909297

    In[2]:= sina2
    General::"spell1": "Possible spelling error: new symbol name "sina2"
    is similar to existing symbol "sin2".
    Out[2]= sina2

    I don't know if some Python IDEs (or IPython) do this already, but it
    can be useful in Pythonwin.


    13) In Mathematica language the = has the same meaning of Python, but
    := is different:

    lhs := rhs assigns rhs to be the delayed value of lhs. rhs is
    maintained in an unevaluated form. When lhs appears, it is replaced by
    rhs, evaluated afresh each time.

    I don't know if this can be useful...


    ------------------

    14) In one of my last emails of notes, I've tried to explain the
    Pattern Matching programming paradigm of Mathematica. Josiah Carlson
    answered me:

    http://groups-beta.google.com/group/comp.lang.python/msg/e15600094cb281c1
    > In the C/C++ world, that is called polymorphism.
    > You can do polymorphism with Python, and decorators may make it

    easier...

    This kind of programming is like the use of a kind regular expression
    on the parameters of functions. Here are some fast operators, from the
    (copyrighted) online help:

    _ or Blank[ ] is a pattern object that can stand for any Mathematica
    expression.
    For example this info comes from:
    http://documents.wolfram.com/mathematica/functions/Blank
    This is used for example in the definition of functions:
    f[x_] := x^2

    __ (two _ characters) or BlankSequence[ ] is a pattern object that can
    stand for any sequence of one or more Mathematica expressions.

    ___ (three _ characters) or BlankNullSequence[ ] is a pattern object
    that can stand for any sequence of zero or more Mathematica
    expressions.
    ___h or BlankNullSequence[h] can stand for any sequence of expressions,
    all of which have head h.

    p1 | p2 | ... is a pattern object which represents any of the patterns
    pi

    s:eek:bj represents the pattern object obj, assigned the name s. When a
    transformation rule is used, any occurrence of s on the right­hand
    side is replaced by whatever expression it matched on the left­hand
    side. The operator : has a comparatively low precedence. The expression
    x:_+_ is thus interpreted as x:(_+_), not (x:_)+_.

    p:v is a pattern object which represents an expression of the form p,
    which, if omitted, should be replaced by v. Optional is used to specify
    "optional arguments" in functions represented by patterns. The pattern
    object p gives the form the argument should have, if it is present. The
    expression v gives the "default value" to use if the argument is
    absent. Example: the pattern f[x_, y_:1] is matched by f[a], with x
    taking the value a, and y taking the value 1. It can also be matched by
    f[a, b], with y taking the value b.

    p.. is a pattern object which represents a sequence of one or more
    expressions, each matching p.

    p... is a pattern object which represents a sequence of zero or more
    expressions, each matching p.

    patt /; test is a pattern which matches only if the evaluation of test
    yields True.
    Example: f[x_] := fp[x] /; x > 1 defines a function in the case when a.
    lhs := Module[{vars}, rhs /; test] allows local variables to be shared
    between test and rhs. You can use the same construction with Block and
    With.

    p?test is a pattern object that stands for any expression which matches
    p, and on which the application of test gives True. Ex:
    p1[x_?NumberQ] := Sqrt[x]
    p2[x_?NumericQ] := Sqr[x]

    Verbatim[expr] represents expr in pattern matching, requiring that expr
    be matched exactly as it appears, with no substitutions for blanks or
    other transformations. Verbatim[x_] will match only the actual
    expression x_. Verbatim is useful in setting up rules for transforming
    other transformation rules.

    HoldPattern[expr] is equivalent to expr for pattern matching, but
    maintains expr in an unevaluated form.

    Orderless is an attribute that can be assigned to a symbol f to
    indicate that the elements a in expressions of the form f[e1, e2, ...]
    should automatically be sorted into canonical order. This property is
    accounted for in pattern matching.

    Flat is an attribute that can be assigned to a symbol f to indicate
    that all expressions involving nested functions f should be flattened
    out. This property is accounted for in pattern matching.

    OneIdentity is an attribute that can be assigned to a symbol f to
    indicate that f[x], f[f[x]], etc. are all equivalent to x for the
    purpose of pattern matching.

    Default[f], if defined, gives the default value for arguments of the
    function f obtained with a _. pattern object.
    Default[f, i] gives the default value to use when _. appears as the
    i-th argument of f.

    Cases[{e1, e2, ...}, pattern] gives a list of the a that match the
    pattern.
    Cases[{e1, e2, ...}, pattern -> rhs] gives a list of the values of rhs
    corresponding to the ei that match the pattern.

    Position[expr, pattern] gives a list of the positions at which objects
    matching pattern appear in expr.

    Select[list, crit] picks out all elements a of list for which crit[ei]
    is True.

    DeleteCases[expr, pattern] removes all elements of expr which match
    pattern.
    DeleteCases[expr, pattern, levspec] removes all parts of expr on levels
    specified by levspec which match pattern.
    Example : DeleteCases[{1, a, 2, b}, _Integer] ==> {a, b}

    Count[list, pattern] gives the number of elements in list that match
    pattern.

    MatchQ[expr, form] returns True if the pattern form matches expr, and
    returns False otherwise.

    It may look strange, but an expert can even use it to write small full
    programs... But usually they are used just when necessary.
    Note that I'm not suggesting to add those (all) into python.

    ------------------

    15) NetLogo is a kind of logo derived from StarLogo, implemented in
    Java.
    http://ccl.northwestern.edu/netlogo/
    I think it contains some ideas that can be useful for Python too.
    - It has built-in some hi-level data structures, like the usual turtle
    (but usually you use LOTS of turtles at the same time, in parallel),
    and the patch (programmable cellular automata layers, each cell can be
    programmed and it can interact with nearby cells or nearby turtles)
    - It contains built-in graphics, because it's often useful for people
    that starts to program, and it's useful for lots of other things. In
    Python it can be useful a tiny and easy "fast" graphics library
    (Tkinter too can be used, but something simpler can be useful for some
    quick&dirty graphics. Maybe this library can also be faster than the
    Tkinter pixel plotting and the pixel matrix visualisation).
    - It contains few types of built-in graphs to plot variables, etc. (for
    python there are many external plotters).
    - Its built-in widgets are really easy to use (they are defined inside
    NetLogo and StarLogo source), but they probably look too much toy-like
    for Python programs...
    - This language contains lots of other nice ideas. Some of them
    probably look too much toy-like, still some examples:
    http://ccl.northwestern.edu/netlogo/models/
    Show that this language is only partially a toy, and it can be useful
    to understand and learn nonlinear dynamics of many systems.

    This is a source, usually some parts of it (like widget positioning and
    parameters) are managed by the IDE:
    http://ccl.northwestern.edu/netlogo/models/models/Sample Models/Biology/Fur.nlogo
    Bye,
    bear hugs,
    Bearophile
    , Dec 29, 2004
    #1
    1. Advertising

  2. Doug Holton Guest

    wrote:

    > for i in 1..12: pass
    > for c in "a".."z": pass

    .....
    > @infix
    > def interval(x, y): return range(x, y+1) # 2 parameters needed
    > assert 5 interval 9 == interval(5,9)

    .....
    > 10) There can be something in the middle between the def statement and
    > the lambda.


    These will likely not appear in CPython standard, but Livelogix runs on
    top of the CPython VM and supports ".." sequences and custom infix
    operators: http://logix.livelogix.com/tutorial/5-Standard-Logix.html

    > 11) This is just a wild idea for an alternative syntax to specify a
    > global variable inside a function. From:
    >
    > def foo(x):
    > global y
    > y = y + 2
    > (the last two lines are indented)
    >
    > To:
    >
    > def foo(x): global.y = global.y + 2
    >
    > Beside the global.y, maybe it can exist a syntax like upper.y or
    > caller.y that means the name y in the upper context. upper.upper.y etc.


    This will also likely never appear in Python. I like your idea though.
    I implemented the same exact thing a couple months ago. One
    difference though, you only need to type out the full "global.y" if you
    want to differentiate it from a local variable with the same name.


    > 15) NetLogo is a kind of logo derived from StarLogo, implemented in
    > Java.
    > Show that this language is only partially a toy, and it can be useful
    > to understand and learn nonlinear dynamics of many systems.


    If you want to do something like Netlogo but using Python instead of
    Logo, see: http://repast.sourceforge.net/
    You can script repast in jython or you can script repast.net.

    Also, you might request the NetLogo and StarLogo developers to support
    Jython (in addition to Logo) scripting in their next version (which is
    already in development and supports 3D).
    Doug Holton, Dec 29, 2004
    #2
    1. Advertising

  3. Andrew Dalke Guest

    bearophileHUGS:
    [on Python's O(n) list insertion/deletion) at any place other than tail
    > (My hypothesis: to keep list implementation a bit simpler, to avoid
    > wasting memory for the head buffer, and to keep them a little faster,
    > avoiding the use of the skip index S).


    Add its relative infrequent need.

    > 2) I usually prefer explicit verbose syntax, instead of cryptic symbols
    > (like decorator syntax), but I like the infix Pascal syntax ".." to
    > specify a closed interval (a tuple?) of integers or letters


    > assert 1..9 == tuple(range(1,10))
    > for i in 1..12: pass
    > for c in "a".."z": pass


    It's been proposed several times. I thought there was a PEP
    but I can't find it. One problem with it; what does

    for x in 1 .. "a":

    do? (BTW, it needs to be 1 .. 12 not 1..12 because 1. will be
    interpreted as the floating point value "1.0".)

    What does
    a = MyClass()
    b = AnotherClass()
    for x in a .. b:
    print x

    do? That is, what's the generic protocol? In Pascal it
    works because you also specify the type and Pascal has
    an incr while Python doesn't.

    > 3) I think it can be useful a way to define infix functions, like this
    > imaginary decorator syntax:
    >
    > @infix
    > def interval(x, y): return range(x, y+1) # 2 parameters needed
    >
    > This may allow:
    > assert 5 interval 9 == interval(5,9)


    Maybe you could give an example of when you need this in
    real life?

    What does

    1 + 2 * 3 interval 9 / 3 - 7

    do? That is, what's the precedence? Does this only work
    for binary or is there a way to allow unary or other
    n-ary (including 0-ary?) functions?


    > 4) The printf-style formatting is powerful, but I still think it's
    > quite complex for usual purposes, and I usually have to look its syntax
    > in the docs. I think the Pascal syntax is nice and simpler to remember
    > (especially for someone with a little Pascal/Delphi experience ^_^),


    But to someone with C experience or any language which derives
    its formatting string from C, Python's is easier to understand than
    your Pascal one.

    A Python view is that there should be only one obvious way to do
    a task. Supporting both C and Pascal style format strings breaks
    that. Then again, having both the old % and the new PEP 292 string
    templates means there's already two different ways to do string
    formatting.

    > For example this Delphi program:

    ...
    > const a = -12345.67890;

    ...
    > writeln(a:4:20);

    ...
    > Gives:

    ...
    > -12345.67890000000000000000

    Python says that's

    >>> "%.20f" % -12345.67890

    '-12345.67890000000079453457'

    I don't think Pascal is IEEE enough.

    note also that the Pascal-style formatting strings are less
    capable than Python's, though few people use features like

    >>> "% 2.3f" % -12.34

    '-12.340'
    >>> "% 2.3f" % 12.34

    ' 12.340'


    > 5) From the docs about round:

    ...
    > But to avoid a bias toward rounding up there is another way do this:


    There are even more ways than that. See
    http://www.python.org/peps/pep-0327.html#rounding-algorithms

    The solution chosen was not to change 'round' but to provide
    a new data type -- Decimal. This is in Python 2.4.

    > 6) map( function, list, ...) applies function to every item of list and
    > return a list of the results. If list is a nested data structure, map
    > applies function to just the upper level objects.
    > In Mathematica there is another parameter to specify the "level" of the
    > apply.

    ..
    > I think this semantic can be extended:


    A real-life example would also be helpful here.

    What does
    map(len, "Blah", level = 200)
    return?

    In general, most people prefer to not use map and instead
    use list comprehensions and (with 2.4) generator comprehensions.


    > level=0 means that the map is performed up to the leaves (0 means
    > infinitum, this isn't nice, but it can be useful because I think Python
    > doesn't contain a built-in Infinite).


    You need to learn more about the Pythonic way of thinking
    of things. The usual solution for this is to have "level = None".

    > 7) Maybe it can be useful to extended the reload(module) semantic:
    > reload(module [, recurse=False])
    > If recurse=True it reloads the module and recursively all the modules
    > that it imports.


    It isn't that simple. Reloading modules isn't sufficient.
    Consider

    import spam
    a = spam.Eggs()
    reload(spam)
    print isinstance(a, spam.Eggs)

    This will print False because a contains a reference to
    the old Eggs which contains a reference to the old spam module.

    As I recall, Twisted has some super-reload code that may be
    what you want. See
    http://twistedmatrix.com/documents/current/api/twisted.python.rebuild.html

    > 8) Why reload is a function and import is a statement? (So why isn't
    > reload a statement too, or both functions?)


    import uses the underlying __import__ function.

    Consider using the __import__ function directly

    math = __import__("math")

    The double use of the name "math" is annoying and error prone.

    It's more complicated with module hierarchies.

    >>> xml = __import__("xml.sax.handler")
    >>> xml.sax.handler

    <module 'xml.sax.handler' from '/sw/lib/python2.3/xml/sax/handler.pyc'>
    >>> xml.sax.saxutils

    Traceback (most recent call last):
    File "<stdin>", line 1, in ?
    AttributeError: 'module' object has no attribute 'saxutils'
    >>> __import__("xml.sax.saxutils")

    <module 'xml' from '/sw/lib/python2.3/xml/__init__.pyc'>
    >>> xml.sax.saxutils

    <module 'xml.sax.saxutils' from '/sw/lib/python2.3/xml/sax/saxutils.pyc'>
    >>>



    Reload takes a reference to the module to reload. Consider
    import UserString
    x = UserString
    reload(x)

    This reloads UserString. It could be a statement but there's
    no advantage to doing so.


    > 9) Functions without a return statement return None: def foo(x): print x
    > I think the compiler/interpreter can give a "compilation warning" where
    > such function results are assigned to something: y = foo(x)


    You might think so but you'ld be wrong.

    Consider

    def vikings():
    pass

    def f():
    global vikings
    def vikings():
    print "Spammity spam!"
    return 1.0

    if random.random() > 0.5:
    f()

    x = vikings()

    More realistically I've done

    class DebugCall:
    def __init__(self, obj):
    self.__obj = obj
    def __call__(self, *args, **kwargs):
    print "Calling", self.__obj, "with", args, kwargs
    x = self.__obj(*args, **kwargs)
    print "Returned with", x
    return x

    from wherever import f
    f = DebugCall(f)

    I don't want it generating a warning for those cases where
    the implicit None is returned.

    A more useful (IMHO) is to have PyChecker check for cases
    where both explicit and implicit returns can occur in the
    same function. Don't know if it does that already.

    Why haven't you looked at PyChecker to see what it does?

    > (I know that some of such cases cannot be spotted at compilation time,
    > but the other cases can be useful too). I don't know if PyChecker does
    > this already. Generally speaking I'd like to see some of those checks
    > built into the normal interpreter. Instructions like:
    > open = "hello"
    > Are legal, but maybe a "compilation warning" can be useful here too (and
    > maybe even a runtime warning if a Verbose flag is set).


    There's a PEP for that. See
    http://www.python.org/peps/pep-0329.html

    Given your questions it would be appropriate for you to read all the
    PEPs.

    > 10) There can be something in the middle between the def statement and
    > the lambda. For example it can be called "fun" (or it can be called
    > "def" still). With it maybe both def and lambdas aren't necessary
    > anymore. Examples:
    > cube = fun x:
    > return x**3
    > (the last line is indented)
    >
    > sorted(data, fun x,y: return x-y)
    > (Probably now it's almost impossible to modify this in the language.)


    It's been talked about. Problems are:
    - how is it written?
    - how big is the region between a lambda an a def?

    Try giving real world examples of when you would
    use this 'fun' and compare it to lambda and def forms.
    you'll find there's at most one extra line of code
    needed. That doesn't seem worthwhile.

    >
    > 11) This is just a wild idea for an alternative syntax to specify a
    > global variable inside a function. From:
    >
    > def foo(x):
    > global y
    > y = y + 2
    > (the last two lines are indented)
    >
    > To:
    >
    > def foo(x): global.y = global.y + 2
    >
    > Beside the global.y, maybe it can exist a syntax like upper.y or
    > caller.y that means the name y in the upper context. upper.upper.y etc.


    It does have the advantage of being explicit rather than
    implicit.

    > 12) Mathematica's interactive IDE suggests possible spelling errors;


    I don't know anything about the IDEs. I have enabled the
    tab-complete in my interactive Python session which is nice.

    I believe IPython is the closest to giving a Mathematica-like feel.
    There's also tmPython.

    > 13) In Mathematica language the = has the same meaning of Python, but
    > := is different:
    >
    > lhs := rhs assigns rhs to be the delayed value of lhs. rhs is maintained
    > in an unevaluated form. When lhs appears, it is replaced by rhs,
    > evaluated afresh each time.
    >
    > I don't know if this can be useful...


    Could you explain why it might be useful?

    > 14) In one of my last emails of notes, I've tried to explain the Pattern
    > Matching programming paradigm of Mathematica. Josiah Carlson answered
    > me:


    Was there a question in all that?

    You are proposing Python include a Prolog-style (or
    CLIPS or Linda or ..) programming idiom, yes? Could you
    also suggest a case when one would use it?

    > 15) NetLogo is a kind of logo derived from StarLogo, implemented in
    > Java.


    How about the "turtle" standard library?

    I must say it's getting pretty annoying to say things like
    "when would this be useful?" and "have you read the documentation?"
    for your statements.

    > Maybe this library can also be faster than the Tkinter pixel
    > plotting and the pixel matrix visualisation).


    See also matplotlib, chaco, and other libraries that work hard
    to make this simple. Have you done any research on what Python
    can do or do you think ... no, sorry, I'm getting snippy.

    Andrew
    Andrew Dalke, Dec 29, 2004
    #3
  4. Paul Rubin Guest

    Andrew Dalke <> writes:
    > What does
    > a = MyClass()
    > b = AnotherClass()
    > for x in a .. b:
    > print x
    >
    > do? That is, what's the generic protocol?


    ".." just becomes an operator like + or whatever, which you can define
    in your class definition:

    class MyClass:
    def __dotdot__(self, other):
    return xrange(self.whatsit(), other.whatsit())

    The .. operation is required to return an iterator.
    Paul Rubin, Dec 29, 2004
    #4
  5. wrote:
    > 4) The printf-style formatting is powerful, but I still think it's
    > quite complex for usual purposes, and I usually have to look its syntax
    > in the docs. I think the Pascal syntax is nice and simpler to remember
    > (especially for someone with a little Pascal/Delphi experience ^_^), it
    > uses two ":" to format the floating point numbers (the second :number
    > is optional). For example this Delphi program:
    >
    > {$APPTYPE CONSOLE}
    > const a = -12345.67890;
    > begin
    > writeln(a);
    > writeln(a:2:0);
    > writeln(a:4:2);
    > writeln(a:4:20);
    > writeln(a:12:2);
    > end.
    >
    > Gives:
    > -1.23456789000000E+0004
    > -12346
    > -12345.68
    > -12345.67890000000000000000
    > -12345.68
    > (The last line starts with 3 spaces)


    Even after looking at your example, I have no idea what the two numbers
    on each side of the :'s do. The last number appears to be the number of
    decimal places to round to, but I don't know what the first number does.

    Since I can't figure it out intuitively (even with examples), I don't
    think this syntax is any less inscrutable than '%<width>.<decimals>f'.
    My suspicion is that you're just biased by your previous use of Pascal.
    (Note that I never used Pascal or enough C to use string formatting
    before I used Python, so I'm less biased than others may be in this
    situation.)

    > 6) map( function, list, ...) applies function to every item of list and
    > return a list of the results. If list is a nested data structure, map
    > applies function to just the upper level objects.
    > In Mathematica there is another parameter to specify the "level" of the
    > apply.
    >
    > So:
    > map(str, [[1,[2]], 3])
    > ==>
    > ['[1, [2]]', '3']
    >
    > With a hypothetical level (default level = 1, it gives the normal
    > Python map):
    >
    > map(str, [[1,[2]], 3], level=1)
    > ==>
    > ['[1, [2]]', '3']
    >
    > map(str, [[1,[2]], 3], level=2)
    > ==>
    > ['1', '[2]', '3']
    >
    > I think this semantic can be extended:
    > level=0 means that the map is performed up to the leaves (0 means
    > infinitum, this isn't nice, but it can be useful because I think Python
    > doesn't contain a built-in Infinite).
    > level=-1 means that the map is performed to the level just before the
    > leaves.
    > Level=-n means that the map is performed n levels before the leaves.


    This packs two things into map -- the true mapping behavior (applying a
    function to a list) and the flattening of a list. Why don't you lobby
    for a builtin flatten instead? (Also, Google for flatten in the
    python-list -- you should find a recent thread about it.)

    > 10) There can be something in the middle between the def statement and
    > the lambda. For example it can be called "fun" (or it can be called
    > "def" still). With it maybe both def and lambdas aren't necessary
    > anymore. Examples:
    > cube = fun x:
    > return x**3
    > (the last line is indented)
    >
    > sorted(data, fun x,y: return x-y)
    > (Probably now it's almost impossible to modify this in the language.)


    Google the python-list for 'anonymous function' or 'anyonymous def' and
    you'll find a ton of discussion about this kind of thing. I'll note
    only that your first example gains nothing over

    def cube(x):
    return x**3

    and that your second example gains nothing over

    sorted(data, lambda x, y: return x-y)

    or

    sorted(data, operator.sub)


    > 11) This is just a wild idea for an alternative syntax to specify a
    > global variable inside a function. From:
    >
    > def foo(x):
    > global y
    > y = y + 2
    > (the last two lines are indented)
    >
    > To:
    >
    > def foo(x): global.y = global.y + 2


    Well, you can do:

    def foo(x):
    globals()['y'] = globals()['y'] + 2

    Not exactly the same syntax, but pretty close.


    > 13) In Mathematica language the = has the same meaning of Python, but
    > := is different:
    >
    > lhs := rhs assigns rhs to be the delayed value of lhs. rhs is
    > maintained in an unevaluated form. When lhs appears, it is replaced by
    > rhs, evaluated afresh each time.
    >
    > I don't know if this can be useful...


    You can almost get this behavior with lambdas, e.g.:

    x = lambda: delayed_expression()

    then you can get a new instance of the expression by simply doing:

    new_instance = x()

    I know this isn't exactly what you're asking for, but this is one
    current possibility that does something similar. You might also look at:

    http://www.python.org/peps/pep-0312.html

    which suggests a simpler syntax for this kind of usage.


    Steve
    Steven Bethard, Dec 29, 2004
    #5
  6. Andrew Dalke wrote:
    > I must say it's getting pretty annoying to say things like
    > "when would this be useful?" and "have you read the documentation?"
    > for your statements.


    I'll second that. Please, "Bearophile", do us the courtesy of checking

    (1) Google groups archive of the mailing list:
    http://groups-beta.google.com/group/comp.lang.python

    and

    (2) The Python Enhancement Proposals:
    http://www.python.org/peps/

    before posting another such set of questions. While most of the people
    on this list are nice enough to answer your questions anyway, the
    answers are already out there for at least half of your questions, if
    you would do us the courtesy of checking first.

    Thanks!

    Steve
    Steven Bethard, Dec 29, 2004
    #6
  7. Andrew Dalke Guest

    Paul Rubin wrote:
    > ".." just becomes an operator like + or whatever, which you can define
    > in your class definition:
    >
    > class MyClass:
    > def __dotdot__(self, other):
    > return xrange(self.whatsit(), other.whatsit())
    >
    > The .. operation is required to return an iterator.


    Ahh, I see.

    This should be put into a PEP. Some obvious questions:
    - ".." or "..." ? The latter is already available for
    use in slices

    - If "..." should the name be "__ellipsis__"? If ".."
    should the name be "__range___"?

    - Should range(x, y) first attempt x.__range__(y)?

    - Can it be used outside of a for statement? Ie, does
    x = "a" ... "b"
    return a generic iterator? Almost certainly as that
    fits in nicely with the existing 'for' syntax.

    - What's the precedence? Given
    x = a .. b .. c
    x = 1 + 2 .. 5 * 3
    x = 1 ** 5 .. 4 ** 2
    etc., what is meant? Most likely .. should have the
    lowest precedence, evaluated left to right.

    - is there an "__rdotdot__"?

    - any way to specify "use the normal beginning"? Like
    for x in .. 5: # same as 0 .. 5
    -or (the oft rejected)-
    for x in 5:

    - any way to specify "ad infinitum"? Like
    for x in 0 .. Infinity:
    -or-
    for x in 0 ... :

    - does "for x in 10 .. 0" the same as xrange(10,0) (what
    you propose) or xrange(10, 0, -1)?

    - do strings work for len(s) > 1? Eg, "A000" .. "A999"?

    - What do you think of (assuming the use of "...")
    for x in 0.....100:?

    - What's the advantage of ".." over, say a function or
    method? That is, why does the new binary operator
    prove so useful? In one of my gedanken experiments
    I considered getting the 10th through 20th prime
    for x in primes(10) .. primes(20):
    but that seems clumsier than
    for x in primes_between(10, 20):
    in part because it requires "primes(10)" to have some
    meaning. I suppose
    for x in primes(10) .. 20:
    could also work though that should in my mind generate
    primes up to the number 20 and not the 20th prime.
    Note that primes(10) cannot return the 10th prime as
    the value 29.

    Andrew
    Andrew Dalke, Dec 29, 2004
    #7
  8. Mike Meyer Guest

    writes:

    > @infix
    > def interval(x, y): return range(x, y+1) # 2 parameters needed
    >
    > This may allow:
    > assert 5 interval 9 == interval(5,9)


    I don't like the idea of turning words into operators. I'd much rather
    see something like:

    @infix('..')
    def interval(x, y):
    return range(x, y + 1)

    assert 5 .. 9 == interval(5, 10)

    This would also allow us to start working on doing away with the magic
    method names for current operators, which I think would be an
    improvement.

    As others have pointed out, you do need to do something about operator
    precedence. For existing operators, that's easy - they keep their
    precedence. For new operators, it's harder.

    You also need to worry about binding order. At the very least, you
    can specify that all new operators bind left to right. But that might
    not be what you want.

    <mike
    --
    Mike Meyer <> http://www.mired.org/home/mwm/
    Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.
    Mike Meyer, Dec 29, 2004
    #8
  9. Steve Holden Guest

    Mike Meyer wrote:

    > writes:
    >
    >
    >>@infix
    >>def interval(x, y): return range(x, y+1) # 2 parameters needed
    >>
    >>This may allow:
    >>assert 5 interval 9 == interval(5,9)

    >
    >
    > I don't like the idea of turning words into operators. I'd much rather
    > see something like:
    >
    > @infix('..')
    > def interval(x, y):
    > return range(x, y + 1)
    >
    > assert 5 .. 9 == interval(5, 10)
    >
    > This would also allow us to start working on doing away with the magic
    > method names for current operators, which I think would be an
    > improvement.
    >

    Well, perhaps you can explain how a change that's made at run time
    (calling the decorator) can affect the parser's compile time behavior,
    then. At the moment, IIRC, the only way Python code can affect the
    parser's behavior is in the __future__ module, which must be imported at
    the very head of a module.

    > As others have pointed out, you do need to do something about operator
    > precedence. For existing operators, that's easy - they keep their
    > precedence. For new operators, it's harder.
    >

    Clearly you'd need some mechanism to specify preference, either
    relatively or absolutely. I seem to remember Algol 68 allowed this.

    > You also need to worry about binding order. At the very least, you
    > can specify that all new operators bind left to right. But that might
    > not be what you want.
    >

    Associativity and precedence will also have to affect the parsing of the
    code, of course. Overall this would be a very ambitious change.

    regards
    Steve
    --
    Steve Holden http://www.holdenweb.com/
    Python Web Programming http://pydish.holdenweb.com/
    Holden Web LLC +1 703 861 4237 +1 800 94 3119
    Steve Holden, Dec 29, 2004
    #9
  10. Mike Meyer Guest

    Steve Holden <> writes:

    > Mike Meyer wrote:
    >
    >> writes:
    >>
    >>>@infix
    >>>def interval(x, y): return range(x, y+1) # 2 parameters needed
    >>>
    >>>This may allow:
    >>>assert 5 interval 9 == interval(5,9)

    >> I don't like the idea of turning words into operators. I'd much
    >> rather
    >> see something like:
    >> @infix('..')
    >> def interval(x, y):
    >> return range(x, y + 1)
    >> assert 5 .. 9 == interval(5, 10)
    >> This would also allow us to start working on doing away with the
    >> magic
    >> method names for current operators, which I think would be an
    >> improvement.
    >>

    > Well, perhaps you can explain how a change that's made at run time
    > (calling the decorator) can affect the parser's compile time behavior,
    > then. At the moment, IIRC, the only way Python code can affect the
    > parser's behavior is in the __future__ module, which must be imported
    > at the very head of a module.


    By modifying the parsers grammer at runtime. After all, it's just a
    data structure that's internal to the compiler.

    <mike
    --
    Mike Meyer <> http://www.mired.org/home/mwm/
    Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.
    Mike Meyer, Dec 29, 2004
    #10
  11. Steve Holden Guest

    Mike Meyer wrote:

    > Steve Holden <> writes:
    >

    [...]
    >>
    >>Well, perhaps you can explain how a change that's made at run time
    >>(calling the decorator) can affect the parser's compile time behavior,
    >>then. At the moment, IIRC, the only way Python code can affect the
    >>parser's behavior is in the __future__ module, which must be imported
    >>at the very head of a module.

    >
    >
    > By modifying the parsers grammer at runtime. After all, it's just a
    > data structure that's internal to the compiler.
    >

    But the parser executes before the compiled program runs, was my point.
    What strange mixture of compilation and interpretation are you going to
    use so the parser actually understands that ".." (say) is an operator
    before the operator definition has been executed?

    regards
    Steve
    --
    Steve Holden http://www.holdenweb.com/
    Python Web Programming http://pydish.holdenweb.com/
    Holden Web LLC +1 703 861 4237 +1 800 494 3119
    Steve Holden, Dec 29, 2004
    #11
  12. Terry Reedy Guest

    "Steven Bethard" <> wrote in message
    news:TLqAd.719331$mD.298058@attbi_s02...
    > I'll second that. Please, "Bearophile", do us the courtesy of checking
    >
    > (1) Google groups archive of the mailing list:
    > http://groups-beta.google.com/group/comp.lang.python
    >
    > and
    >
    > (2) The Python Enhancement Proposals:
    > http://www.python.org/peps/
    >
    > before posting another such set of questions. While most of the people
    > on this list are nice enough to answer your questions anyway, the answers
    > are already out there for at least half of your questions, if you would
    > do us the courtesy of checking first.


    I also suggest perusing the archived PyDev (Python Development mailing
    list) summaries for the last couple of years (see python.org). Every two
    weeks, Brett Cannon has condensed everything down to a few pages. You can
    easily focus on the topics of interest to you. For instance, there was
    discussion of making lists truly double-ended, but it was decided to settle
    for certain improvements in the list implementation while adding
    collections.deque (sp?) in 2.4.

    Terry J. Reedy
    Terry Reedy, Dec 29, 2004
    #12
  13. Terry Reedy Guest

    "Mike Meyer" <> wrote in message
    news:...
    > Steve Holden <> writes:
    >> Well, perhaps you can explain how a change that's made at run time
    >> (calling the decorator) can affect the parser's compile time behavior,
    >> then. At the moment, IIRC, the only way Python code can affect the
    >> parser's behavior is in the __future__ module, which must be imported
    >> at the very head of a module.

    >
    > By modifying the parsers grammer at runtime. After all, it's just a
    > data structure that's internal to the compiler.


    Given that xx.py is parsed in its entirety *before* runtime, that answer is
    no answer at all. Runtime parser changes (far, far from trivial) could
    only affect the result of exec and eval.

    Terry J. Reedy
    Terry Reedy, Dec 29, 2004
    #13
  14. On Wed, 29 Dec 2004 11:42:00 -0600, Mike Meyer <> wrote:

    > writes:
    >
    >> @infix
    >> def interval(x, y): return range(x, y+1) # 2 parameters needed
    >>
    >> This may allow:
    >> assert 5 interval 9 == interval(5,9)

    >
    >I don't like the idea of turning words into operators. I'd much rather
    >see something like:
    >
    >@infix('..')
    >def interval(x, y):
    > return range(x, y + 1)
    >
    >assert 5 .. 9 == interval(5, 10)
    >

    I like that for punctuation-character names.

    OTOH, there is precedent in e.g. fortran (IIRC) for named operators of the
    form .XX. -- e.g., .GE. for >= so maybe there could be room for both.

    A capitalization _convention_ would make such infix operators pretty readable
    even if the names were'nt always the best, e.g.,

    for x in 5 .UP_TO_AND_INCLUDING. 9:
    ...

    Hm, you could make

    x .infix. y

    syntactic sugar in general (almost like a macro) for

    infix(x, y)

    and you could generalize that to permit .expression. with no embedded spaces, e.g.,

    x .my_infix_module.infix. y
    for
    my_infix_module.infix(x, y)

    or to illustrate expression generality ridiculously,

    a = x .my_infix_module.tricky_func_factory_dict[random.choice(range(4))](time.time()). y

    for
    a = my_infix_module.tricky_func_factory_dict[random.choice(range(4))](time.time())(x, y)

    <aside>
    I wonder if it's a good idea to post ridiculous but functionally illustrative uses
    of possibly good ideas, or if the net effect detracts from the reception of the ideas.
    Also verbiage like this ;-/
    </aside>

    If '..' were special-cased as a synonym for __nullname__ you could handle it
    by def __nullname__(x, y): whatever, but since it's punctuation-only, your @infix('..')
    seem preferable.

    Hm, ... if single (to exlude .infix.) missing dotted names defaulted to __nullname__,
    I wonder what that would open up ;-) obj. would be obj.__nullname__, which could be
    defined as a concise way of referring to the one special attribute or property.
    And .name would be __nullname__.name -- which with the approriate descriptor definition
    in the function class could make .name syntactic sugar for self.name (or whatever the first arg
    name was). ... just musing ;-)

    >This would also allow us to start working on doing away with the magic
    >method names for current operators, which I think would be an
    >improvement.
    >
    >As others have pointed out, you do need to do something about operator
    >precedence. For existing operators, that's easy - they keep their
    >precedence. For new operators, it's harder.
    >
    >You also need to worry about binding order. At the very least, you
    >can specify that all new operators bind left to right. But that might
    >not be what you want.

    Yes. My .expression. infix if implemented essentially as a left-right
    rewrite-as-soon-as-you-recognize macro would create the precedence rules
    of the macro-rewritten source. Which might cover a fair amount of useful
    ground. Needs to be explored though. E.g.,

    x .op1. y .op2. z => op2(op1(x, y), z)

    But you could override with parens in the ordinary way:

    x .op1. (y .op2. z) => op1(x, op2(y, z))

    But
    2 * x + 3 .op1. y => 2 * x + op1(3, y)

    Etc. Well, something to think about ;-)


    Regards,
    Bengt Richter
    Bengt Richter, Dec 30, 2004
    #14
  15. Andrew Dalke Guest

    Bengt Richter:
    > OTOH, there is precedent in e.g. fortran (IIRC) for named operators of the
    > form .XX. -- e.g., .GE. for >= so maybe there could be room for both.


    > Hm, you could make
    >
    > x .infix. y



    > x .op1. y .op2. z => op2(op1(x, y), z)


    The problem being that that's already legal syntax

    >>> class Xyzzy:

    .... def __init__(self):
    .... self.op1 = self.op2 = self.y = self
    .... self.z = "Nothing happens here"
    ....
    >>> x = Xyzzy()
    >>> x .op1. y .op2. z

    'Nothing happens here'
    >>>


    Andrew
    Andrew Dalke, Dec 30, 2004
    #15
  16. On Wed, 29 Dec 2004 13:11:43 -0500, Steve Holden <> wrote:

    >Mike Meyer wrote:
    >
    >> writes:
    >>
    >>
    >>>@infix
    >>>def interval(x, y): return range(x, y+1) # 2 parameters needed
    >>>
    >>>This may allow:
    >>>assert 5 interval 9 == interval(5,9)

    >>
    >>
    >> I don't like the idea of turning words into operators. I'd much rather
    >> see something like:
    >>
    >> @infix('..')
    >> def interval(x, y):
    >> return range(x, y + 1)
    >>
    >> assert 5 .. 9 == interval(5, 10)
    >>
    >> This would also allow us to start working on doing away with the magic
    >> method names for current operators, which I think would be an
    >> improvement.
    >>

    >Well, perhaps you can explain how a change that's made at run time
    >(calling the decorator) can affect the parser's compile time behavior,
    >then. At the moment, IIRC, the only way Python code can affect the
    >parser's behavior is in the __future__ module, which must be imported at
    >the very head of a module.

    Good point, which I didn't address in my reply. (in fact I said I liked
    @infix('..') for punctuation-char-named ops, but I was too busy with my
    idea to think about that implementation ;-)

    Potentially, you could do it dynamically with a frame flag (to limit the damage)
    which said, check all ops against a dict of overloads and infix definitions while
    executing byte code for this frame. Of course, the compiler would have to defer
    some kinds of syntax error 'til run time. I.e., '..' would have to be translated
    to OP_POSSIBLE_CUSTOM_INFIX or such. I doubt if it would be worth doing.

    OTOH, I think my suggestion might be ;-) I.e., just do a macro-like (not a general
    macro capability for this!!) translation of expressions with dots at both ends and
    no embedded spaces (intial thought, to make things easier) thus:
    x .expr. y => expr(x, y)

    when expr is a simple name, you can use that expression format to call a two-arg function
    of that name, e.g.,

    def interval(x, y): return xrange(x, y+1)
    for i in x .interval. y: print i, # same as for i in interval(x, y): print i,

    but you could also write stuff like

    def GE(x,y): return x is MY_INFINITY or x >= y
    if x .GE. y: print 'x is greater than y'

    The .expr. as expression would allow module references or tapping into general
    expression and attribute magic etc. I.e., (untested)

    from itertools import chain as CHAIN
    for k,v in d1.items() .CHAIN. d2.items(): print k, v

    or if you had itertools imported and liked verbose infix spelling:

    for k,v in d1.items() .itertools.chain. d2.items(): print k, v

    or define a hidden-attribute access operation using an object's dict

    def HATTR(obj, i):
    try: return vars(obj)
    except KeyError: raise AttributeError('No such attribute: %r', i)

    if thing .HATTR. 2 == 'two': print 'well spelled'

    or
    from rational import rat as RAT

    if x .RAT. y > 1 .RAT. 3: do_it()

    or
    your turn ;-)

    >
    >> As others have pointed out, you do need to do something about operator
    >> precedence. For existing operators, that's easy - they keep their
    >> precedence. For new operators, it's harder.
    >>

    >Clearly you'd need some mechanism to specify preference, either
    >relatively or absolutely. I seem to remember Algol 68 allowed this.
    >
    >> You also need to worry about binding order. At the very least, you
    >> can specify that all new operators bind left to right. But that might
    >> not be what you want.
    >>

    >Associativity and precedence will also have to affect the parsing of the
    >code, of course. Overall this would be a very ambitious change.
    >

    My suggestion if implemented with left-right priority would be easy to
    implement (I think ;-) And you could always override order with parens.

    Regards,
    Bengt Richter
    Bengt Richter, Dec 30, 2004
    #16
  17. On Thu, 30 Dec 2004 03:37:38 GMT, Andrew Dalke <> wrote:

    >Bengt Richter:
    >> OTOH, there is precedent in e.g. fortran (IIRC) for named operators of the
    >> form .XX. -- e.g., .GE. for >= so maybe there could be room for both.

    >
    >> Hm, you could make
    >>
    >> x .infix. y

    >
    >
    >> x .op1. y .op2. z => op2(op1(x, y), z)

    >
    >The problem being that that's already legal syntax

    D'oh ;-)

    >
    >>>> class Xyzzy:

    >... def __init__(self):
    >... self.op1 = self.op2 = self.y = self
    >... self.z = "Nothing happens here"
    >...
    >>>> x = Xyzzy()
    >>>> x .op1. y .op2. z

    >'Nothing happens here'
    >>>>


    Ok, well, that's happened to me before ;-)
    We'll have to find a way to make it illegal, but it's not likely to be quite as clean.

    x ..OP y
    x ./OP y
    x .<OP y
    x .<OP>. y
    X ._OP_. y
    x ..OP.. y # for symmetry ;-)

    X .(OP). y # emphasizes the .expression. returning a function accepting two args

    That might be the best one.

    OTOH some time ago I was thinking of .(statements). as a possible tokenizer-time star-gate into
    a default-empty tokenizer-dynamically-created module which would essentially exec the statements
    in that module and return the value of the last expression as a string for insertion into the token
    source code stream at that point being tokenized.

    Thus e.g. you could have source that said

    compile_time = .(__import__('time').ctime()).

    and get a time stamp string into the source text at tokenization time.

    I had also thought obj.(expr) could be syntactic sugar for obj.__dict__[expr]
    but that would also interfere ;-)

    So maybe .(OP). should for infix, and .[stargate exec args]. should be for that ;-)

    Regards,
    Bengt Richter
    Bengt Richter, Dec 30, 2004
    #17
  18. On Thu, 30 Dec 2004 03:55:12 GMT, (Bengt Richter) wrote:
    [.. buncha stuff alzheimersly based on x<spaces>.attr not being parsed as x.attr ;-/ ]

    > from rational import rat as RAT
    >
    > if x .RAT. y > 1 .RAT. 3: do_it()
    >
    >or
    > your turn ;-)
    >

    Andrew got there first ;-)
    Still, see my reply to his for more opportunities ;-)

    Regards,
    Bengt Richter
    Bengt Richter, Dec 30, 2004
    #18
  19. On Thu, 30 Dec 2004 04:46:25 GMT, (Bengt Richter) wrote:
    [...]
    >Ok, well, that's happened to me before ;-)
    >We'll have to find a way to make it illegal, but it's not likely to be quite as clean.
    >
    > x ..OP y
    > x ./OP y
    > x .<OP y
    > x .<OP>. y
    > X ._OP_. y

    Bzzzt! ;-/

    > x ..OP.. y # for symmetry ;-)
    >
    > X .(OP). y # emphasizes the .expression. returning a function accepting two args
    >
    >That might be the best one.


    Regards,
    Bengt Richter
    Bengt Richter, Dec 30, 2004
    #19
  20. Steve Holden Guest

    Bengt Richter wrote:

    > On Wed, 29 Dec 2004 13:11:43 -0500, Steve Holden <> wrote:
    >

    [...]
    >>
    >>Well, perhaps you can explain how a change that's made at run time
    >>(calling the decorator) can affect the parser's compile time behavior,
    >>then. At the moment, IIRC, the only way Python code can affect the
    >>parser's behavior is in the __future__ module, which must be imported at
    >>the very head of a module.

    >
    > Good point, which I didn't address in my reply. (in fact I said I liked
    > @infix('..') for punctuation-char-named ops, but I was too busy with my
    > idea to think about that implementation ;-)
    >

    Well, that explains the lack of detail. I realize that you are more
    likely than most to be able to come up with an implementation.

    > Potentially, you could do it dynamically with a frame flag (to limit the damage)
    > which said, check all ops against a dict of overloads and infix definitions while
    > executing byte code for this frame. Of course, the compiler would have to defer
    > some kinds of syntax error 'til run time. I.e., '..' would have to be translated
    > to OP_POSSIBLE_CUSTOM_INFIX or such. I doubt if it would be worth doing.
    >

    Right. I can't say I think deferring syntax errors until runtime is a
    good idea.

    > OTOH, I think my suggestion might be ;-) I.e., just do a macro-like (not a general
    > macro capability for this!!) translation of expressions with dots at both ends and
    > no embedded spaces (intial thought, to make things easier) thus:
    > x .expr. y => expr(x, y)
    >
    > when expr is a simple name, you can use that expression format to call a two-arg function
    > of that name, e.g.,
    >
    > def interval(x, y): return xrange(x, y+1)
    > for i in x .interval. y: print i, # same as for i in interval(x, y): print i,
    >
    > but you could also write stuff like
    >
    > def GE(x,y): return x is MY_INFINITY or x >= y
    > if x .GE. y: print 'x is greater than y'
    >
    > The .expr. as expression would allow module references or tapping into general
    > expression and attribute magic etc. I.e., (untested)
    >
    > from itertools import chain as CHAIN
    > for k,v in d1.items() .CHAIN. d2.items(): print k, v
    >
    > or if you had itertools imported and liked verbose infix spelling:
    >
    > for k,v in d1.items() .itertools.chain. d2.items(): print k, v
    >
    > or define a hidden-attribute access operation using an object's dict
    >
    > def HATTR(obj, i):
    > try: return vars(obj)
    > except KeyError: raise AttributeError('No such attribute: %r', i)
    >
    > if thing .HATTR. 2 == 'two': print 'well spelled'
    >
    > or
    > from rational import rat as RAT
    >
    > if x .RAT. y > 1 .RAT. 3: do_it()
    >
    > or
    > your turn ;-)
    >

    Well, I can see that Fortran programmers might appreciate it :). And I
    suppose that the syntax is at least regular enough to be lexed with the
    current framework, give or take. It would lead to potential breakage due
    to the syntactic ambiguity between

    module .function. attribute

    and

    module.function.attribute

    though I don't honestly think that most people currently insert
    gratuitous spaces into attribute references.

    >

    [precedence and associativity]
    >
    > My suggestion if implemented with left-right priority would be easy to
    > implement (I think ;-) And you could always override order with parens.


    Now you're just trying to make it easy :)

    regards
    Steve
    --
    Steve Holden http://www.holdenweb.com/
    Python Web Programming http://pydish.holdenweb.com/
    Holden Web LLC +1 703 861 4237 +1 800 494 3119
    Steve Holden, Dec 30, 2004
    #20
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. Bjorn Jensen
    Replies:
    0
    Views:
    1,171
    Bjorn Jensen
    Mar 22, 2005
  2. raymond chiu

    Lotus Notes and DotNet

    raymond chiu, Dec 23, 2005, in forum: ASP .Net
    Replies:
    1
    Views:
    736
    Scott M.
    Dec 27, 2005
  3. Boris Condarco

    ASP.NET vs Lotus Notes

    Boris Condarco, Jul 29, 2003, in forum: ASP .Net
    Replies:
    1
    Views:
    482
    Dino Chiesa [MSFT]
    Jul 30, 2003
  4. Jp Calderone

    Re: Other notes

    Jp Calderone, Dec 29, 2004, in forum: Python
    Replies:
    11
    Views:
    502
    Bengt Richter
    Jan 8, 2005
  5. SteveM
    Replies:
    5
    Views:
    1,550
    Mark Rae [MVP]
    Aug 28, 2007
Loading...

Share This Page