triple quoted strings as comments

Discussion in 'Python' started by dmh2000, Jan 31, 2006.

  1. dmh2000

    dmh2000 Guest

    I recently complained elsewhere that Python doesn't have multiline
    comments. i was told to use triple quoted strings to make multiline
    comments. My question is that since a triple quoted string is actually
    a language construct, does it use cause a runtime construction of a
    string which is then discarded, or is the runtime smart enough to see
    that it isn't used and so it doesn't construct it?

    example

    def fun(self):
    """doc comment
    comment line 2
    """

    x = 1
    y = 2

    """does this triple quoted string used as a comment
    cause something to happen at runtime beyond
    just skipping over it? Such as allocation of memory for a string
    or worse yet garbage collection? or not?
    """
    z = x + y

    ....

    dave howard
    dmh2000, Jan 31, 2006
    #1
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  2. dmh2000

    Guest

    as i know, the triple quoted string does cause a runtime construction,
    and will not be discarded, and it's a benefit of python language.
    here is sth. useful.
    _http://diveintopython.org/power_of_introspection/index.html

    best regard
    , Jan 31, 2006
    #2
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  3. dmh2000

    Peter Hansen Guest

    dmh2000 wrote:
    > I recently complained elsewhere that Python doesn't have multiline
    > comments. i was told to use triple quoted strings to make multiline
    > comments. My question is that since a triple quoted string is actually
    > a language construct, does it use cause a runtime construction of a
    > string which is then discarded, or is the runtime smart enough to see
    > that it isn't used and so it doesn't construct it?


    Easy enough to find out. Put this in test.py:

    'first module comment'
    'another'

    def func():
    'first func comment'
    'another'
    print 'hi'
    'last one'

    'and last module comment'


    Now do "import test" from the Python prompt, then exit the interpreter
    and do "strings test.pyc" on the compiled bytecode.

    (The short answer is only the first such comments are kept.)

    -Peter
    Peter Hansen, Jan 31, 2006
    #3
  4. dmh2000 wrote:
    > I recently complained elsewhere that Python doesn't have multiline
    > comments. i was told to use triple quoted strings to make multiline
    > comments. My question is that since a triple quoted string is actually
    > a language construct, does it use cause a runtime construction of a
    > string which is then discarded, or is the runtime smart enough to see
    > that it isn't used and so it doesn't construct it?
    >
    > example
    >
    > def fun(self):
    > """doc comment
    > comment line 2
    > """
    >
    > x = 1
    > y = 2
    >
    > """does this triple quoted string used as a comment
    > cause something to happen at runtime beyond
    > just skipping over it? Such as allocation of memory for a string
    > or worse yet garbage collection? or not?
    > """
    > z = x + y

    It seems to discard the second triple quoted comment (the first one is
    kept around as a doc string).
    I created two scripts, one with the second triple quoted string, the
    other without. The compiled version is *almost* the same (one byte
    difference which, if I am not mistaken, comes from the different
    filename embedded in the .pyc file).

    30/01/2006 09:34 PM 327 triple.py
    30/01/2006 09:35 PM 359 triple.pyc
    30/01/2006 09:34 PM 96 triple2.py
    30/01/2006 09:35 PM 358 triple2.pyc
    André
    =?iso-8859-1?B?QW5kcuk=?=, Jan 31, 2006
    #4
  5. dmh2000

    Roy Smith Guest

    "dmh2000" <> wrote:
    > I recently complained elsewhere that Python doesn't have multiline
    > comments.


    Of course it has multi-line comments. They look like this:

    # This is the first line
    # and this is the second.

    Why is that a problem?
    Roy Smith, Jan 31, 2006
    #5
  6. On 30 Jan 2006 16:29:15 -0800
    "dmh2000" <> wrote:
    > I recently complained elsewhere that Python doesn't have
    > multiline comments. i was told to use triple quoted
    > strings to make multiline comments. My question is that
    > since a triple quoted string is actually a language
    > construct, does it use cause a runtime construction of a
    > string which is then discarded, or is the runtime smart
    > enough to see that it isn't used and so it doesn't
    > construct it?
    >
    > example
    >
    > def fun(self):
    > """doc comment
    > comment line 2
    > """


    This is specifically a "docstring" so it remains attached as
    an attribute of fun: fun.__doc__

    > x = 1
    > y = 2
    >
    > """does this triple quoted string used as a comment
    > cause something to happen at runtime beyond
    > just skipping over it? Such as allocation of memory
    > for a string or worse yet garbage collection? or
    > not?
    > """


    This string is really unused. It will produce a value when
    processed the first time, but it's not bound so it gets
    immediately garbage-collected. And it won't be there after
    the module is byte-compiled. So, you lose a little time the
    very first time the file is used (but that's technically
    true for a regular comment too -- I think this loses you a
    little more time). But it's pretty trivial in practice,
    because every subsequent time, it's gone.

    > z = x + y



    At least, this is how I understand it.

    Cheers,
    Terry


    --
    Terry Hancock ()
    Anansi Spaceworks http://www.AnansiSpaceworks.com
    Terry Hancock, Jan 31, 2006
    #6
  7. dmh2000

    Steve Holden Guest

    dmh2000 wrote:
    > I recently complained elsewhere that Python doesn't have multiline
    > comments.


    Personally I think it's a win that you couldn't find anything more
    serious to complain about :)

    regards
    Steve
    --
    Steve Holden +44 150 684 7255 +1 800 494 3119
    Holden Web LLC www.holdenweb.com
    PyCon TX 2006 www.python.org/pycon/
    Steve Holden, Jan 31, 2006
    #7
  8. dmh2000

    Duncan Booth Guest

    dmh2000 wrote:

    > example
    >
    > def fun(self):
    > """doc comment
    > comment line 2
    > """
    >
    > x = 1
    > y = 2
    >
    > """does this triple quoted string used as a comment
    > cause something to happen at runtime beyond
    > just skipping over it? Such as allocation of memory for a string
    > or worse yet garbage collection? or not?
    > """
    > z = x + y
    >


    How to find out for yourself:

    >>> def fun(self):

    """doc comment
    comment line 2
    """

    x = 1
    y = 2

    """does this triple quoted string used as a comment
    cause something to happen at runtime beyond
    just skipping over it? Such as allocation of memory for a string
    or worse yet garbage collection? or not?
    """
    z = x + y


    >>> import dis
    >>> dis.dis(fun)

    6 0 LOAD_CONST 1 (1)
    3 STORE_FAST 2 (x)

    7 6 LOAD_CONST 2 (2)
    9 STORE_FAST 1 (y)

    14 12 LOAD_FAST 2 (x)
    15 LOAD_FAST 1 (y)
    18 BINARY_ADD
    19 STORE_FAST 3 (z)
    22 LOAD_CONST 3 (None)
    25 RETURN_VALUE
    >>>


    Further inspection shows that it hasn't even saved that second string as a
    constant:

    >>> print fun.func_code.co_consts

    ('doc comment\n comment line 2\n ', 1, 2, None)
    Duncan Booth, Jan 31, 2006
    #8
  9. Steve Holden wrote:
    > dmh2000 wrote:
    >
    >> I recently complained elsewhere that Python doesn't have multiline
    >> comments.

    >
    >
    > Personally I think it's a win that you couldn't find anything more
    > serious to complain about :)


    +1 QOTW
    Jeffrey Schwab, Jan 31, 2006
    #9
  10. dmh2000

    Magnus Lycka Guest

    dmh2000 wrote:
    > I recently complained elsewhere that Python doesn't have multiline
    > comments.

    It seems you have a bad editor if it can't conveniently
    add and remove comment markers for arbitrary blocks in
    your source. (Maybe you just didn't find this feature.)

    That every comment line begins with a special symbol just
    adds clarity. It's a bonus. C++ introduced // as comment
    symbol for this purpose (but was stuck with /* and */ due
    to backward compatibility reasons). Ada, while otherwise
    similar to Pascal, adopted -- to end of row instead of (*
    and *) etc.

    An editor that adds/removes '# ' in the beginning of each
    marked line is fairly bullet proof. Adding e.g. /* to the
    beginning of a block you want to comment out, & */ to the
    end, breaks if you have /* */ style comments in the block!
    Magnus Lycka, Feb 1, 2006
    #10
  11. dmh2000

    Roy Smith Guest

    Magnus Lycka <> wrote:
    > An editor that adds/removes '# ' in the beginning of each
    > marked line is fairly bullet proof. Adding e.g. /* to the
    > beginning of a block you want to comment out, & */ to the
    > end, breaks if you have /* */ style comments in the block!


    /* */ also allows for some truly spectacularly bad coding practices. Not
    long ago, I ran into some real-life code where a previous developer had
    commented out about 50 lines of C++ code by just putting a /* at the top
    and a */ at the bottom. I was tearing my hair out trying to figure out how
    the code worked until I noticed what he had done.
    Roy Smith, Feb 1, 2006
    #11
  12. Roy Smith schreef:
    > Magnus Lycka <> wrote:
    >> An editor that adds/removes '# ' in the beginning of each
    >> marked line is fairly bullet proof. Adding e.g. /* to the
    >> beginning of a block you want to comment out, & */ to the
    >> end, breaks if you have /* */ style comments in the block!

    >
    > /* */ also allows for some truly spectacularly bad coding practices. Not
    > long ago, I ran into some real-life code where a previous developer had
    > commented out about 50 lines of C++ code by just putting a /* at the top
    > and a */ at the bottom. I was tearing my hair out trying to figure out how
    > the code worked until I noticed what he had done.


    That happened to me a few times. These days I use an editor with syntax
    highlighting that shows comments in another color than code. That helps
    tremendously.

    --
    If I have been able to see further, it was only because I stood
    on the shoulders of giants. -- Isaac Newton

    Roel Schroeven
    Roel Schroeven, Feb 1, 2006
    #12
  13. dmh2000

    Jorgen Grahn Guest

    On Wed, 01 Feb 2006 13:41:33 GMT, Roel Schroeven <> wrote:
    > Roy Smith schreef:

    ....
    >> /* */ also allows for some truly spectacularly bad coding practices. Not
    >> long ago, I ran into some real-life code where a previous developer had
    >> commented out about 50 lines of C++ code by just putting a /* at the top
    >> and a */ at the bottom. I was tearing my hair out trying to figure out how
    >> the code worked until I noticed what he had done.

    >
    > That happened to me a few times. These days I use an editor with syntax
    > highlighting that shows comments in another color than code. That helps
    > tremendously.


    Syntax highlighting, same here. Plus version control so you can see who did
    it, and make a mental note not to trust that person in the future ;-)

    ("#if 0" in C and C++ are better choices, but only marginally. Best is to
    remove the code unless you are sure it's needed again soon. Works in all
    languages.)

    /Jorgen

    --
    // Jorgen Grahn <grahn@ Ph'nglui mglw'nafh Cthulhu
    \X/ snipabacken.dyndns.org> R'lyeh wgah'nagl fhtagn!
    Jorgen Grahn, Feb 5, 2006
    #13
  14. Jorgen Grahn wrote:
    >>> [...] developer had
    >>> commented out about 50 lines of C++ code by just putting a /* at the top
    >>> and a */ at the bottom.

    [...]
    > ("#if 0" in C and C++ are better choices, but only marginally. Best is to
    > remove the code unless you are sure it's needed again soon. Works in all
    > languages.)


    However, I'd only advise to do this if you are using a revision control.
    Otherwise, you'll end up having a lot of "backup" files hanging around
    which are even worse than multi-row comments. Or, even worse: If you
    don't create backup files before removing code ...


    Greets,

    Volker

    --
    Volker Grabsch
    ---<<(())>>---
    \frac{\left|\vartheta_0\times\{\ell,\kappa\in\Re\}\right|}{\sqrt
    [G]{-\Gamma(\alpha)\cdot\mathcal{B}^{\left[\oint\!c_\hbar\right]}}}
    Volker Grabsch, Feb 6, 2006
    #14
  15. dmh2000

    Jorgen Grahn Guest

    On 6 Feb 2006 12:53:53 GMT, Volker Grabsch <> wrote:
    > Jorgen Grahn wrote:
    >>>> [...] developer had
    >>>> commented out about 50 lines of C++ code by just putting a /* at the top
    >>>> and a */ at the bottom.

    > [...]
    >> ("#if 0" in C and C++ are better choices, but only marginally. Best is to
    >> remove the code unless you are sure it's needed again soon. Works in all
    >> languages.)

    >
    > However, I'd only advise to do this if you are using a revision control.


    But surely, everybody's using revision control these days?
    (Feel free to smile at my naivety now ;-)

    /Jorgen

    --
    // Jorgen Grahn <grahn@ Ph'nglui mglw'nafh Cthulhu
    \X/ snipabacken.dyndns.org> R'lyeh wgah'nagl fhtagn!
    Jorgen Grahn, Feb 6, 2006
    #15
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