1

The answer in this post details nicely how python inner functions don't use the value of closure variables until the inner function actually executes, finding the variable name in the proper scope.

For example:

funcs = [(lambda: x) for x in range(3)]

Calling any of the generated lambdas returns 2:

>>> funcs[0]()
2
>>> funcs[1]()
2
>>> funcs[2]()
2

Is there a way to force the value for x to be determined when the function is defined instead of when it is executed later? In the above example, my desired output is 0, 1, 2, respectively.

More specifically, my use-case is to provide a way for API users to conveniently turn a custom function into a thread using a decorator. For example:

for idx in range(3):
    @thread_this(name=f'thread_{idx}')
    def custom():
        do_something()
        print(f'thread_{idx} complete.')

When the final print statement executes, it picks up whatever the current value of idx is in the global scope. With appropriate sleep statements, all 3 threads will print 'thread_2 complete.'

drootang
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1 Answers1

0

You can use functools.partial, first problem can be solved with,

funcs = [functools.partial(lambda x: x, x) for x in xrange(3)]

It will give you desired result. However, I could not understand the second usecase.

pnv
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