Alphones wrote:
> On 11月26日, 下午9时28分, [EMAIL PROTECTED] wrote:
>> Alphones:
>>
>> > it is a little deferent from other script language.
>>
>> See also here:http://en.wikipedia.org/wiki/Dynamic_scope#Dynamic_scoping
>>
>> Python doesn't have such automatic closures, probably for performance
>> reasons and/or maybe to keep its C implementation simpler (maybe other
>> people here can give you an explanation of this, I too am curious).
>>
>> Bye,
>> bearophile
>
> i encountered this problem when i'm writing a program for packaging
> files.
> the program generates tasks according to description file.
> and tasks are deferent from each other, and should be excuted at the
> last of program.
>
> i have experience on Lua and have learned about scheme and haskell, so
> i wrote the wrong code in python.
>
> now my solution is, using class taskCreator to create tasks and put
> them into tasklist.
> class taskCreator:
> def __init__(self, proc, input, output):
> self.proc = proc
> self.input = input
> self.output = output
> def call(self):
> return self.proc.call(self.input, self.output)
> 'proc' is generated by procCreators, it's specified.
>
> it looks more complex than lambda one.
>
> is there any other simple way to implement it?
Yes, you can have closures in Python (you already had one, the getFunc()
function in your initial post).
Random remarks:
You don't need an explicit call() method, you can make instances callable:
>>> class A:
... def __init__(self, name):
... self.name = name
... def __call__(self):
... print "calling", self.name
...
>>> a = A("foo")
>>> a()
calling foo
If your object has just this one method you can instead use a closure:
>>> def make_a(name):
... def call():
... print "calling", name
... return call
...
>>> a = make_a("bar")
>>> a()
calling bar
This can be simplified further with some help from the library:
>>> from functools import partial
>>> def call(name):
... print "calling", name
...
>>> a = partial(call, "baz")
>>> a()
calling baz
Here is a complete example:
import sys
from functools import partial
def lower(input, output):
output.writelines(line.lower() for line in input)
def prefix(input, output):
for index_line in enumerate(input):
output.write("%d: %s" % index_line)
tasks = [partial(lower, open("tmp.py"), sys.stdout),
partial(prefix, open("tmp.py"), sys.stdout)]
for t in tasks:
t()
Peter
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