Connecting function name to another function using a variable as name

Question

For a school project about artificial intelligence, I need to be able to connect a function name to another function like this for example:

def b_test(x):
    return x+1

def a_test(x):
    return x

variable = "b"
variable+= "_test"
a_test = variable

But this happenned

I guess that Python wants to use the name "b" as the new name/alias of the function a_test instead of using b_test as the new name.

So how can I force python to look what b means instead of just using it?

EDIT:

What I want to do is :

I have in my variable variable the string b and I need to, when I use in my code a_test(x), return x+1 (the return of the function b_test). So I add the string "_test" to variable so it is "b_test".

I could do it by coding

a_test = b_test

but I won't only connect a_test to b_test, it might be c_test or d_test, that's why I need to use a variable.

Ummm, [`getattr()`](https://docs.python.org/2/library/functions.html#getattr)? — zwer, Apr 05 '18 at 08:47
This is quite unclear to me - no idea what you want to accomplish. Elaborate? Also: dont post pictures of errors, copy and paste its text and stacktrace. --- http://idownvotedbecau.se/imageofanexception/ — Patrick Artner, Apr 05 '18 at 08:47
Exercise: does speaking the word *"France"* take you to the country by that name? (Don't try this at home!) — tripleee, Apr 05 '18 at 08:58
Peter Wood : no, but mlp_function.b_test exists (a_test too) — Nathan Marotte, Apr 05 '18 at 09:07

score 0 · Accepted Answer · answered Apr 05 '18 at 09:12

Your example should work actually, but it doesn't reflect your actual code and error from the screenshot. In your screenshot, you are trying to get the ChosenFunction from mlp_functions module, which does not have that attribute, hence the AttributeError. To get the attribute from a module using a str name, you would need to use getattr like:

mlp_functions.logistic_function = getattr(mlp_functions, ChosenFunction)

score 0 · Answer 2 · answered Apr 05 '18 at 09:20

First of all you need to construct the function name (from your variable) and retrieve the module name so you can load the python function object in the variable you need.

Here is the code:

def b_test(x):
    return x + 1


def a_test(x):
    return x


def main():
    # Construct function name
    test_option = "b"  # "a"                                                                                                                                                                                                                                                   
    test_name = test_option + "_test"

    # Retrieve function module
    import os
    import importlib
    module_name = os.path.splitext(os.path.basename(__file__))[0]
    module = importlib.import_module(module_name)

    # Retrieve function
    test = getattr(module, test_name)

    # Debug information
    if __debug__:
        print ("Current file: " + str(__file__))
        print ("Module name: " + str(module_name))
        print ("Module: " + str(module))
        print ("Test function name: " + str(test_name))
        print ("Test function: " + str(test))

    # Execute function
    result = test(1)
    print ("Result: " + str(result))


if __name__ == '__main__':
    main()

Some important notes:

The test option will be just a string containing the test function you want to load.
Instead of "renaming" the a_test function, just use a test variable that points to the correct function to execute
The getattr function is a little bit tricky with file names and modules so if you modify this code you maybe want to modify the way the function module is computed.

Connecting function name to another function using a variable as name

2 Answers2