removing list comprehensions in Python 3.0
steven.bethard at gmail.com
Sun Jul 10 06:32:22 CEST 2005
Raymond Hettinger wrote:
> [Steven Bethard]
>>I would hope that in Python 3.0 list comprehensions and generator
>>expressions would be able to share a large amount of implementation, and
>>thus that the speed differences would be much smaller. But maybe not...
> Looking under the hood, you would see that the implementations are
> necessarily as different as night and day. Only the API is similar.
Necessarily? It seems like list comprehensions *could* be implemented
as a generator expression passed to the list constructor. They're not
now, and at the moment, changing them to work this way seems like a bad
idea because list comprehensions would take a performance hit. But I
don't understand why the implementations are *necessarily* different.
Could you explain?
P.S. The dis.dis output for list comprehensions makes what they're doing
pretty clear. But dis.dis doesn't seem to give me as much information
when looking at a generator expression:
py> def ge(items):
... return (item for item in items if item)
2 0 LOAD_CONST 1 (<code object <generator
expression> at 0116FD20, file "<interactive input>", line 2>)
3 MAKE_FUNCTION 0
6 LOAD_FAST 0 (items)
10 CALL_FUNCTION 1
I tried to grep through the dist\src directories for what a generator
expression code object looks like, but without any luck. Any chance you
could point me in the right direction?
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