Scott David Daniels wrote:
Denis Kasak wrote:
...
spam = []
for i in range(10):
... spam.append(lambda: i)
spam[0]()
9
spam[1]()
9
Manually creating the lambdas and appending them to a list works as
expected, naturally; I don't see a good reason why it wouldn't work
with a loop. Am I missing something?
Yes, you are missing something: binding time. your anonymous function
returns the value of "i" in the enclosing scope _at_the_time_of_
_the function's_execution_. If you follow your previous example with
'del i' and then execute any of your spam functions, you'll get an
"NameError: global name 'i' is not defined".
Ah, the problem was in the subtle misunderstanding of the semantics of
lambda functions on my part. It's much clearer now. Thanks.
There are a couple of ways to slve your problem:
(1) use default args to do the binding at the function definition time.
for i in range(10):
spam.append(lambda arg=i: arg)
The lambda expression is normally spelled "lambda i=i: i)", but if you
don't know the idiom, I find the "i=i" part confuses people.
Indeed. It hasn't occured to me that lambdas could bind the variables
inside them by name. I guess my lambdas are still a little shaky. :-)
--
Denis Kasak
--
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