lambda

[Egor Bolonev]

why functions created with lambda forms cannot contain statements?

how to get unnamed function with statements?

[Daniel Dittmar]

Egor Bolonev wrote:

why functions created with lambda forms cannot contain statements?
syntax/technical answer: because lambda is an expression and it is not
obvious how the syntax for 'statement inside expression' should be

'Python is perfect' answer: if a function contains more than an
expression, then it's complex enough to require a name
how to get unnamed function with statements?

You can't. See various threads about Smalltalk/Ruby-like blocks and the
recent one about the 'where' keyword for proposals to change this

Daniel

[Tim Leslie]

Because if it takes more than a single line it deserves a name. Also,
if you have more than one line in this function, how do you plan to
reference it if not by name?

Tim
On Thu, 13 Jan 2005 20:53:09 +1000, Egor Bolonev <eb******@mail. ru> wrote:

why functions created with lambda forms cannot contain statements?

how to get unnamed function with statements?
--
http://mail.python.org/mailman/listinfo/python-list

[Antoon Pardon]

Op 2005-01-13, Tim Leslie schreef <ti********@gma il.com>:

Because if it takes more than a single line it deserves a name.

So if I have a call with an expression that takes more than
one line, I should assign the expression to a variable and
use the variable in the call?

But wait if I do that, people will tell me how bad that it
is, because it will keep a reference to the value which
will prevent the garbage collector from harvesting this
memory.

Besides python allows more than one statement on the same line.

--
Antoon Pardon

[hanz]

Antoon Pardon wrote:

So if I have a call with an expression that takes more than
one line, I should assign the expression to a variable and
use the variable in the call?
Yes, that's sometimes a good practice and can clarify
the call.
But wait if I do that, people will tell me how bad that it
is, because it will keep a reference to the value which
will prevent the garbage collector from harvesting this
memory.
Nobody will tell you that it's bad. Python was never
about super performance, but about readability.
Besides, using such temporaries won't consume much
memory (relatively).
Besides python allows more than one statement on the same line.

But it's discouraged in general.

[Paul Rubin]

"hanz" <ha******@yahoo .com.au> writes:

But wait if I do that, people will tell me how bad that it is,
because it will keep a reference to the value which will prevent
the garbage collector from harvesting this memory.

Nobody will tell you that it's bad. Python was never about super
performance, but about readability. Besides, using such temporaries
won't consume much memory (relatively).

That completely depends on the objects in question. Compare

temp = all_posters[:]
temp.sort()
top_five_poster s = temp[-5:]

to:

top_five_poster s = all_posters.sor ted()[-5:]

which became possible only when .sorted() was added to Python 2.4.

This is another reason it would be nice to be able to create very
temporary scopes.

[Steven Bethard]

Paul Rubin wrote:

That completely depends on the objects in question. Compare

temp = all_posters[:]
temp.sort()
top_five_poster s = temp[-5:]

to:

top_five_poster s = all_posters.sor ted()[-5:]

which became possible only when .sorted() was added to Python 2.4.

I believe you mean "when sorted() was added to Python 2.4":

py> ['d', 'b', 'c', 'a'].sorted()
Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
AttributeError: 'list' object has no attribute 'sorted'
py> sorted(['d', 'b', 'c', 'a'])
['a', 'b', 'c', 'd']

Note that sorted is a builtin function, not a method of a list object.
It takes any iterable and creates a sorted list from it. Basically the
equivalent of:

def sorted(iterable ):
result = list(iterable)
result.sort()
return result

Steve

[Paul Rubin]

Steven Bethard <st************ @gmail.com> writes:

Note that sorted is a builtin function, not a method of a list
object.

Oh, same difference. I thought it was a method because I'm not using
2.4 yet. The result is the same, other than that having it as a
function instead of a method is another inconsistency to remember.

[Fredrik Lundh]

Paul Rubin wrote:

Note that sorted is a builtin function, not a method of a list
object.
Oh, same difference. I thought it was a method because I'm not using
2.4 yet. The result is the same

nope. sorted works on any kind of sequence, including forward-only
iterators. sorted(open(fil ename)) works just fine, for example.
other than that having it as a function instead of a method is another
inconsistency to remember

I suspect that you don't really understand how sequences and iterators
work in Python...

</F>

[Paul Rubin]

"Fredrik Lundh" <fr*****@python ware.com> writes:

Oh, same difference. I thought it was a method because I'm not using
2.4 yet. The result is the same

nope. sorted works on any kind of sequence, including forward-only
iterators. sorted(open(fil ename)) works just fine, for example.

Oh cool. However I meant the result is the same in my example, where
assigning the temporary result to a variable stopped memory from
getting reclaimed until after the function exits.