Call a function dynamically from a variable - Python

Question

Ok so I have two files, filename1.py and filename2.py and they both have a function with same name funB. The third file process.py has function that calls function from either files. I seem to be struggling in calling the correct function.

In process.py:

from directoryA.filename1 import funB
from directoryA.filename2 import funB

def funA:

    #do stuff to determine which filename and save it in variable named 'd'
    d = 'filename2'
    # here i want to call funB with *args based on what 'd' is

So i have tried eval() like so:

 call_right_funB = eval(d.funB(*args))

but it seems not to work.

Any help is appreciated.

Can't you just from directoryA.filename1 import funB as f1 in this case? Or do you really need to dynamically lookup the module? — Jon Clements
– Jon Clements, Commented Sep 16, 2017 at 9:21
@JonClements Thanks, Yes I need to dynamically look up the module — Darth
– Darth, Commented Sep 16, 2017 at 9:27
They're not "directory.filename" but "package.module" or am I missing something? — Antti Haapala
– Antti Haapala, Commented Sep 16, 2017 at 9:45
@AnttiHaapala its 'package.module' I used 'directory.filename' for simplifying and clarification purpose only — Darth
– Darth, Commented Sep 16, 2017 at 9:49

mdpt · Accepted Answer · 2017-09-16 11:42:07Z

3

The problem is, you can't use eval() with a combination of a string and a method like that. What you have written is:

call_right_funB = eval('filename'.funB(*args))

What you can do is:

call_right_funB = eval(d + '.funB(*args)')

But this is not very pythonic approach. I would recommend creating a dictionary switch. Even though you have to import entire module:

import directoryA.filename1
import directoryA.filename2

dic_switch = {1: directoryA.filename1, 2: directoryA.filename2}
switch_variable = 1
call_right_funB = dic_switch[switch_variable].funB(*args)

Hope it helps.

edited Sep 16, 2017 at 11:42

answered Sep 16, 2017 at 10:07

mdpt

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7 Comments

Darth Over a year ago

Thank you, the first "unpythonic" way works fine. With Dictionary switch how would i call then function 'funB'

mdpt Over a year ago

You are welcome :-) call_right_funB = dict_switch[switch_variable].funB(*args) should work fine. Edit: If you are using it only once, you can also do: call_right_funB = {1: filename1, 2: filename2}[switch_variable].funB(*args)

Darth Over a year ago

I get AttributeError: 'str' object has no attribute 'funB'

mdpt Over a year ago

@darth haven't you write dictionary values as strings? Notice that in dict_switch they are saved as keywords, not as strings.

Darth Over a year ago

It was string but if i save as keywords I get TypeError: 'module' object is not subscriptable

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