On 4/26/06, Schüle Daniel <[EMAIL PROTECTED]> wrote:
> Hello group,
>
> >>> lst=[]
> >>> for i in range(10):
> ... lst.append(eval("lambda:%i" % i))
> ...
> >>> lst[0]()
> 0
> >>> lst[1]()
> 1
> >>> lst[9]()
> 9
> >>>
>
> >>> lst=[]
> >>> for i in range(10):
> ... exec "tmp = lambda:%i" % i # assignment is not expression
> ... lst.append(tmp)
> ...
> >>> lst[0]()
> 0
> >>> lst[1]()
> 1
> >>> lst[9]()
> 9
> >>>
>
> and now the obvious one (as I thought at first)
>
> >>> lst=[]
> >>> for i in range(10):
> ... lst.append(lambda:i)
> ...
> >>> lst[0]()
> 9
> >>> i
> 9
> >>>
>
> I think I understand where the problem comes from
> lambda:i seems not to be fully evalutated
> it just binds object with name i and not the value of i
> thus lst[0]() is not 0
>
> are there other solutions to this problem
> without use of eval or exec?
>
Using a factory function & closures instead of lambda:
>>> def maker(x):
... def inner_maker():
... return x
... return inner_maker
...
>>> lst = []
>>> for i in range(10):
... lst.append(maker(i))
...
>>> lst[0]()
0
>>> lst[5]()
5
>>> lst[9]()
9
>>>
> Regards, Daniel
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> http://mail.python.org/mailman/listinfo/python-list
>
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