Create/Initialize a series of functions from data-CodePudding

I'm trying to initialize a collection of function calls based on input data, but not sure how to do this. The ideas is like below. I expect the local_v will stay unchanged once being defined. Can anyone shed some light how to deal with this or where to start with?

ls = [1,2]
for v in ls:
    def fn():
        local_v = v
        print(local_v)
    locals()[f'print{v}'] = fn

print1() # output: 2 expect to be 1
print2() # output: 2

CodePudding user response：

Better to store the functions in a dictionary rather than changing locals, which is likely to get confusing. You could use a nested function like this:

def function_maker(v):
    def fn():
        print(v)
    return fn

print_functions = {v: function_maker(v) for v in [1, 2]}
print_functions[1]()
print_functions[2]()

Alternatively use functools.partial

from functools import partial

def fn(v):
    print(v)
    
print_functions = {v: partial(fn, v) for v in [1, 2]}

CodePudding user response：

If you want v to be tied to the local context, you'll have to pass it inside the function. You will also need to return a callable to print rather than using the print function directly, or else you will find that print1 and print2 will be None. And at this point, there is no need to redefine fnat each iteration of the loop. Something like that will work:

ls = [1, 2]

def fn(v):
        return lambda: print(v)

for v in ls:
    locals()[f'print{v}'] = fn(v)

print1() # output: 1
print2() # output: 2

Just to try to be clearer: invoking print1() does not call fn(1), it calls the lambda that returned by fn(1).