Flatten a list/tuple and Call a function with tuples

[beginner]

Hi,

I am wondering how do I 'flatten' a list or a tuple? For example, I'd
like to transform[1, 2, (3,4)] or [1,2,[3,4]] to [1,2,3,4].

Another question is how do I pass a tuple or list of all the
aurgements of a function to the function. For example, I have all the
arguments of a function in a tuple a=(1,2,3). Then I want to pass each
item in the tuple to a function f so that I make a function call
f(1,2,3). In perl it is a given, but in python, I haven't figured out
a way to do it. (Maybe apply? but it is deprecated?)

Thanks,
cg

 

[kyosohma]

Hi,

I am wondering how do I 'flatten' a list or a tuple? For example, I'd
like to transform[1, 2, (3,4)] or [1,2,[3,4]] to [1,2,3,4].

Another question is how do I pass a tuple or list of all the
aurgements of a function to the function. For example, I have all the
arguments of a function in a tuple a=(1,2,3). Then I want to pass each
item in the tuple to a function f so that I make a function call
f(1,2,3). In perl it is a given, but in python, I haven't figured out
a way to do it. (Maybe apply? but it is deprecated?)

Thanks,
cg

I'm not sure about the first question, but as for the second, you
could do a few different things. You could just pass the tuple itself
into the function and have the tuple unpacked inside the function.

<code>

f(a)

def f (tuple):
x,y,z = tuple

</code>

You could also pass the elements of the tuple in:

f(a[0], a[1], a[2])

That would do it the way you describe in your post.

Mike

 

[Stargaming]

Hi,

I am wondering how do I 'flatten' a list or a tuple? For example, I'd
like to transform[1, 2, (3,4)] or [1,2,[3,4]] to [1,2,3,4].

A recursive function, always yielding the first element of the list,
could do the job. See the ASPN Python Cookbook for a few implementations.
http://aspn.activestate.com/ASPN/search?
query=flatten&section=PYTHONCKBK&type=Subsection

Another question is how do I pass a tuple or list of all the aurgements
of a function to the function. For example, I have all the arguments of
a function in a tuple a=(1,2,3). Then I want to pass each item in the
tuple to a function f so that I make a function call f(1,2,3). In perl
it is a given, but in python, I haven't figured out a way to do it.
(Maybe apply? but it is deprecated?)

1 2 3

Have a look at the official tutorial, 4.7.4 http://www.python.org/doc/
current/tut/node6.html#SECTION006740000000000000000

Thanks,
cg

HTH,
Stargaming

 

[beginner]

Hi,

I am wondering how do I 'flatten' a list or a tuple? For example, I'd
like to transform[1, 2, (3,4)] or [1,2,[3,4]] to [1,2,3,4].

A recursive function, always yielding the first element of the list,
could do the job. See the ASPN Python Cookbook for a few implementations.http://aspn.activestate.com/ASPN/search?
query=flatten&section=PYTHONCKBK&type=Subsection

Another question is how do I pass a tuple or list of all the aurgements
of a function to the function. For example, I have all the arguments of
a function in a tuple a=(1,2,3). Then I want to pass each item in the
tuple to a function f so that I make a function call f(1,2,3). In perl
it is a given, but in python, I haven't figured out a way to do it.
(Maybe apply? but it is deprecated?)

1 2 3

Have a look at the official tutorial, 4.7.4http://www.python.org/doc/
current/tut/node6.html#SECTION006740000000000000000

Thanks,
cg

HTH,
Stargaming

Hi Stargaming,

I know the * operator. However, a 'partial unpack' does not seem to
work.

def g():
return (1,2)

def f(a,b,c):
return a+b+c

f(*g(),10) will return an error.

Do you know how to get that to work?

Thanks,
cg

 

[kyosohma]

Hi,
I am wondering how do I 'flatten' a list or a tuple? For example, I'd
like to transform[1, 2, (3,4)] or [1,2,[3,4]] to [1,2,3,4].

A recursive function, always yielding the first element of the list,
could do the job. See the ASPN Python Cookbook for a few implementations.http://aspn.activestate.com/ASPN/search?
query=flatten&section=PYTHONCKBK&type=Subsection

1 2 3

Have a look at the official tutorial, 4.7.4http://www.python.org/doc/
current/tut/node6.html#SECTION006740000000000000000

HTH,
Stargaming

Hi Stargaming,

I know the * operator. However, a 'partial unpack' does not seem to
work.

def g():
return (1,2)

def f(a,b,c):
return a+b+c

f(*g(),10) will return an error.

Do you know how to get that to work?

Thanks,
cg

As I mentioned, you can access the elements individually using square
brackets. The following works:

f(g()[0], g()[1], 10)

But it's not clear. Unfortunately, I'm not seeing much else for tuple
unpacking except the obvious:

a,b=g()
f(a,b,10)


Mike

 

[beginner]

On Wed, 25 Jul 2007 14:50:18 +0000, beginner wrote:
Hi,
I am wondering how do I 'flatten' a list or a tuple? For example, I'd
like to transform[1, 2, (3,4)] or [1,2,[3,4]] to [1,2,3,4].
A recursive function, always yielding the first element of the list,
could do the job. See the ASPN Python Cookbook for a few implementations.http://aspn.activestate.com/ASPN/search?
query=flatten&section=PYTHONCKBK&type=Subsection
Another question is how do I pass a tuple or list of all the aurgements
of a function to the function. For example, I have all the arguments of
a function in a tuple a=(1,2,3). Then I want to pass each item in the
tuple to a function f so that I make a function call f(1,2,3). In perl
it is a given, but in python, I haven't figured out a way to do it.
(Maybe apply? but it is deprecated?)
def foo(a, b, c): print a, b, c
...
t = (1, 2, 3)
foo(*t)
1 2 3
Have a look at the official tutorial, 4.7.4http://www.python.org/doc/
current/tut/node6.html#SECTION006740000000000000000
Thanks,
cg
HTH,
Stargaming

Hi Stargaming,

I know the * operator. However, a 'partial unpack' does not seem to
work.

def g():
return (1,2)

def f(a,b,c):
return a+b+c

f(*g(),10) will return an error.

Do you know how to get that to work?

Thanks,
cg

As I mentioned, you can access the elements individually using square
brackets. The following works:

f(g()[0], g()[1], 10)

But it's not clear. Unfortunately, I'm not seeing much else for tuple
unpacking except the obvious:

a,b=g()
f(a,b,10)

Mike- Hide quoted text -

- Show quoted text -

Unfortunately f(g()[0], g()[1], 10) is calling g() twice. Sometimes
this is not a good idea.

a,b=g()
f(a,b,10)

would work until you want it to be an expression.

 

[Diez B. Roggisch]

Hi,

I am wondering how do I 'flatten' a list or a tuple? For example, I'd
like to transform[1, 2, (3,4)] or [1,2,[3,4]] to [1,2,3,4].

A recursive function, always yielding the first element of the list,
could do the job. See the ASPN Python Cookbook for a few
implementations.http://aspn.activestate.com/ASPN/search?
query=flatten&section=PYTHONCKBK&type=Subsection

Another question is how do I pass a tuple or list of all the aurgements
of a function to the function. For example, I have all the arguments of
a function in a tuple a=(1,2,3). Then I want to pass each item in the
tuple to a function f so that I make a function call f(1,2,3). In perl
it is a given, but in python, I haven't figured out a way to do it.
(Maybe apply? but it is deprecated?)
def foo(a, b, c): print a, b, c ...
t = (1, 2, 3)
foo(*t)

1 2 3

Have a look at the official tutorial, 4.7.4http://www.python.org/doc/
current/tut/node6.html#SECTION006740000000000000000

Thanks,
cg

HTH,
Stargaming

Hi Stargaming,

I know the * operator. However, a 'partial unpack' does not seem to
work.

def g():
return (1,2)

def f(a,b,c):
return a+b+c

f(*g(),10) will return an error.

Do you know how to get that to work?

f(*(g() + (10,))

Not the most beautiful solution, but it works.

Diez

 

[Stargaming]

On Wed, 25 Jul 2007 14:50:18 +0000, beginner wrote: [snip]

Another question is how do I pass a tuple or list of all the
aurgements of a function to the function. For example, I have all the
arguments of a function in a tuple a=(1,2,3). Then I want to pass
each item in the tuple to a function f so that I make a function call
f(1,2,3). In perl it is a given, but in python, I haven't figured out
a way to do it. (Maybe apply? but it is deprecated?)
def foo(a, b, c): print a, b, c ...
t = (1, 2, 3)
foo(*t)

1 2 3

Have a look at the official tutorial, 4.7.4http://www.python.org/doc/
current/tut/node6.html#SECTION006740000000000000000

Thanks,
cg

HTH,
Stargaming

Hi Stargaming,

I know the * operator. However, a 'partial unpack' does not seem to
work.

def g():
return (1,2)

def f(a,b,c):
return a+b+c

f(*g(),10) will return an error.
http://docs.python.org/ref/calls.html

Do you know how to get that to work?

Well, there are several ways to solve this. You could either invoke f(*g
() + (10,)). Might be a bit nasty and unreadable, though. Or you could
just change your function f to accept them in reversed order (f(10, *g)
should work) or convert g() to return a dictionary like {'b': 1, 'c': 2}
and use f(10, **g). But if your function f's hugest use case is being
called with g(), changing f to accept something and g's result (tuple) --
unpacking it inside f -- might be better.

 

[Paul Rubin]

I know the * operator. However, a 'partial unpack' does not seem to work.

A few other posters have mentioned ways around this, but you might ask
yourself what coding situation makes you want to do this stuff in the
first place. I won't say there's never a reason for it, but a lot of
times, a list containing a mixture of scalars and lists/tuples is a
sign that your underlying data representation is contorted. Things
are logically single values or they are logically lists of values, and
that mixed representation is often a sign that the item logically
should be a list, and you're hairing up the program with special
treatment of the case where the list has exactly one element.

I.e. instead of [[1,2,], 3, [5,6,]] maybe you really want
[[1,2,], [3,], [5,6]] without the special treatment and flattening.

 

[James Stroud]

Hi,
I am wondering how do I 'flatten' a list or a tuple? For example, I'd
like to transform[1, 2, (3,4)] or [1,2,[3,4]] to [1,2,3,4].

A recursive function, always yielding the first element of the list,
could do the job. See the ASPN Python Cookbook for a few implementations.http://aspn.activestate.com/ASPN/search?
query=flatten&section=PYTHONCKBK&type=Subsection

Another question is how do I pass a tuple or list of all the aurgements
of a function to the function. For example, I have all the arguments of
a function in a tuple a=(1,2,3). Then I want to pass each item in the
tuple to a function f so that I make a function call f(1,2,3). In perl
it is a given, but in python, I haven't figured out a way to do it.
(Maybe apply? but it is deprecated?)
def foo(a, b, c): print a, b, c ...
t = (1, 2, 3)
foo(*t)

1 2 3

Have a look at the official tutorial, 4.7.4http://www.python.org/doc/
current/tut/node6.html#SECTION006740000000000000000

Thanks,
cg

HTH,
Stargaming

Hi Stargaming,

I know the * operator. However, a 'partial unpack' does not seem to
work.

def g():
return (1,2)

def f(a,b,c):
return a+b+c

f(*g(),10) will return an error.

Do you know how to get that to work?

Thanks,
cg

Were this not hypothetical, I would make use of the commutative property
of addition:

f(10, *g())

Proof:

1+2+10 = 10+1+2


Also, this has not been suggested:

py> def g():
.... return (1,2)
....
py> def f(a,b,c):
.... return a+b+c
....
py> f(c=10, *g())
13


James

 

[Wildemar Wildenburger]

I'm not sure about the first question, but as for the second, you
could do a few different things. You could just pass the tuple itself
into the function and have the tuple unpacked inside the function.

OR you could use the syntax invented for just that purpose .

bam!

This works with dicts as well (for giving keyword arguments). There you
prepend ** (two asterisk to your dict).
Simple
/W

 

[attn.steven.kuo]

Hi,
I am wondering how do I 'flatten' a list or a tuple? For example, I'd
like to transform[1, 2, (3,4)] or [1,2,[3,4]] to [1,2,3,4].

A recursive function, always yielding the first element of the list,
could do the job. See the ASPN Python Cookbook for a few implementations.http://aspn.activestate.com/ASPN/search?
query=flatten&section=PYTHONCKBK&type=Subsection

1 2 3

Have a look at the official tutorial, 4.7.4http://www.python.org/doc/
current/tut/node6.html#SECTION006740000000000000000

HTH,
Stargaming

Hi Stargaming,

I know the * operator. However, a 'partial unpack' does not seem to
work.

def g():
return (1,2)

def f(a,b,c):
return a+b+c

f(*g(),10) will return an error.

Do you know how to get that to work?

You can use the "partial" method from functools:

import functools

sum_of_three = functools.partial(f, *g())(10)

 

[George Sakkis]

On Wed, 25 Jul 2007 14:50:18 +0000, beginner wrote:
Hi,
I am wondering how do I 'flatten' a list or a tuple? For example, I'd
like to transform[1, 2, (3,4)] or [1,2,[3,4]] to [1,2,3,4].
A recursive function, always yielding the first element of the list,
could do the job. See the ASPN Python Cookbook for a few implementations.http://aspn.activestate.com/ASPN/search?
query=flatten&section=PYTHONCKBK&type=Subsection
Another question is how do I pass a tuple or list of all the aurgements
of a function to the function. For example, I have all the arguments of
a function in a tuple a=(1,2,3). Then I want to pass each item in the
tuple to a function f so that I make a function call f(1,2,3). In perl
it is a given, but in python, I haven't figured out a way to do it.
(Maybe apply? but it is deprecated?)
def foo(a, b, c): print a, b, c
...
t = (1, 2, 3)
foo(*t)
1 2 3
Have a look at the official tutorial, 4.7.4http://www.python.org/doc/
current/tut/node6.html#SECTION006740000000000000000
Thanks,
cg
HTH,
Stargaming

Hi Stargaming,

I know the * operator. However, a 'partial unpack' does not seem to
work.

def g():
return (1,2)

def f(a,b,c):
return a+b+c

f(*g(),10) will return an error.

Do you know how to get that to work?

Thanks,
cg

As I mentioned, you can access the elements individually using square
brackets. The following works:

f(g()[0], g()[1], 10)

But it's not clear. Unfortunately, I'm not seeing much else for tuple
unpacking except the obvious:

a,b=g()
f(a,b,10)

Mike

Or if you'd rather write it in one line:

f(*(g() + (10,)))

George

 

[Jeff]

Here's a quick flatten() function:

def flatten(obj):
if type(obj) not in (list, tuple, str):
raise TypeError("String, list, or tuple expected in
flatten().")
if len(obj) == 1:
if type(obj[0]) in (tuple, list):
return flatten(obj[0])
else:
return [obj[0]]
else:
return [obj[0]] + flatten(obj[1:])

x = [1, 2, (3, 4)]
y = (1, 2, [3, 4])
z = "It even works with strings!"
d = {"foo": "bar", "baz": "bat"}

print flatten(x)
print flatten(y)
print flatten(z)
print flatten(d)

 

[Aneesh Goel]

def flatten(obj):
if type(obj) not in (list, tuple, str):
raise TypeError("String, list, or tuple expected in
flatten().")
if len(obj) == 1:
if type(obj[0]) in (tuple, list):
return flatten(obj[0])
else:
return [obj[0]]
else:
return [obj[0]] + flatten(obj[1:])

This seems to work fine only if the last object is the only one with
the tuple or list. For example:

y = [(1,2),3,4]
y [(1, 2), 3, 4]
print flatten(y)

[(1, 2), 3, 4]

if the last line is changed to

return flatten([obj[0]]) + flatten(obj[1:])

then it will unpack tuples/lists anywhere in the main collection being
flattened:

y [(1, 2), 3, 4]
flatten(y) [1, 2, 3, 4]
z = [1,(2,3),4]
flatten(z) [1, 2, 3, 4]
x [1, 2, (3, 4)]
flatten(x) [1, 2, 3, 4]
k = [(1,2),(3,4)]
flatten(k)

[1, 2, 3, 4]

 

[Neil Cerutti]

Here's a quick flatten() function:

def flatten(obj):
if type(obj) not in (list, tuple, str):
raise TypeError("String, list, or tuple expected in
flatten().")
if len(obj) == 1:
if type(obj[0]) in (tuple, list):
return flatten(obj[0])
else:
return [obj[0]]
else:
return [obj[0]] + flatten(obj[1:])

x = [1, 2, (3, 4)]
y = (1, 2, [3, 4])
z = "It even works with strings!"
d = {"foo": "bar", "baz": "bat"}

e = [[1], 2, 3, , 4]
f = [1, 2, 3, 4, []]

 

[Neil Cerutti]

Here's a quick flatten() function:

def flatten(obj):
if type(obj) not in (list, tuple, str):
raise TypeError("String, list, or tuple expected in
flatten().")
if len(obj) == 1:
if type(obj[0]) in (tuple, list):
return flatten(obj[0])
else:
return [obj[0]]
else:
return [obj[0]] + flatten(obj[1:])

x = [1, 2, (3, 4)]
y = (1, 2, [3, 4])
z = "It even works with strings!"
d = {"foo": "bar", "baz": "bat"}

e = [[1], 2, 3, , 4]

Please excuse my bad typography. The above should've been

e = [[1], 2, 3, 4].

 

[Eduardo \EdCrypt\ O. Padoan]

def flatten(listOfLists):
return list(chain(*listOfLists))

 

[Jeff]

Sorry about that. Hopefully, this should work

def flatten(obj):
if type(obj) not in (list, tuple, str):
raise TypeError("String, list, or tuple expected in
flatten().")
if len(obj) == 1:
if type(obj[0]) in (tuple, list):
return flatten(obj[0])
else:
return [obj[0]]
else:
if type(obj[0]) in (list, tuple):
return flatten(obj[0]) + flatten(obj[1:])
else:
return [obj[0]] + flatten(obj[1:])


x = (1, 2, [3, 4, (5, 6)])
y = ([1, 2, (3, 4)], 5, 6)
z = (1, [2, 3, (4, 5)], 6)

print flatten(x)
print flatten(y)
print flatten(z)

 

[Jeff]

def flatten(listOfLists):
return list(chain(*listOfLists))

That doesn't necessarily work:

import itertools

x = (1, 2, [3, 4, (5, 6)])
y = ([1, 2, (3, 4)], 5, 6)
z = (1, [2, 3, (4, 5)], 6)

def flatten(listOfLists):
return list(itertools.chain(*listOfLists))

print flatten(x)
print flatten(y)
print flatten(z)

==> TypeError: chain argument #1 must support iteration