lambda in list comprehension acting funny
steve+comp.lang.python at pearwood.info
Sun Jul 15 10:32:47 CEST 2012
On Sun, 15 Jul 2012 10:49:48 +1000, Chris Angelico wrote:
> On Sun, Jul 15, 2012 at 9:29 AM, Steven D'Aprano
> <steve+comp.lang.python at pearwood.info> wrote:
>> Not necessarily *compile* time, but the distinction is between when the
>> function is defined (which may at compile time, or it may be at run
>> time) versus when the function is called.
> I'd treat the def/lambda statement as "compile time" and the () operator
> as "run time".
But function definitions occur at run time, not compile time -- they are
executable statements, not instructions to the compiler to define a
py> dis("def f(x): return x+1") # Python 3.2
1 0 LOAD_CONST 0 (<code object f at 0xb7b57de0,
file "<dis>", line 1>)
3 MAKE_FUNCTION 0
6 STORE_NAME 0 (f)
9 LOAD_CONST 1 (None)
The code object is pre-compiled at compile time, but the function and
name-binding (the "def") doesn't occur until runtime.
At compile time, Python parses the source code and turns it into byte-
code. Class and function definitions are executed at run time, the same
as any other statement.
I'm not sure if this is a difference that makes a difference or not; I
think it is, but don't know enough about how closures and scoping rules
work in other languages to be sure that it does make a difference.
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