python dynamic from module import function by string

Question

The origin code is(simplify for example):

#!/usr/bin/env python
# -*- coding: utf-8 -*-
from utils.func_a import func_a as _func_a
from utils.func_b import func_b as _func_b
def func_a():
    _func_a()

def func_b():
    _func_b()

if __name__ == '__main__':
    func_a()

now I only called func_a, or maybe func_b, it depends on configuration.

so I want to dynamic do from ... import ..., such as:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
def func_a():
    _func_a()

def func_b():
    _func_b()

if __name__ == '__main__':
    keys = ['func_a']
    for k in keys:
        mod_n = func_n = k
        from utils.<mod_n> import <func_n> as _<func_n>   # TODO
    func_a()

but I don't know to how to implement it?

What I have thought is do import in func_X():

#!/usr/bin/env python
# -*- coding: utf-8 -*-
def func_a():
    from utils.func_a import func_a as _func_a
    _func_a()

def func_b():
    from utils.func_b import func_b as _func_b
    _func_b()

if __name__ == '__main__':
    func_a()

but this way will do import every time when call function.

Supplement:

I have tried __import__ / importlib, but can't implement this condition

With regards to your last example: imports are cached, so the modules you mention will not be imported every time you call the functions. Read more here. — Wander Nauta
– Wander Nauta, Commented Aug 11, 2015 at 9:30

Community · Accepted Answer · 2020-06-20 09:12:55Z

2

__import__ is a builtin function which takes the module name as a string and returns the module as an object. See the documentation:

__import__(name[, globals[, locals[, fromlist[, level]]]])
The function imports the module name, potentially using the given globals and locals to determine how to interpret the name in a package context. The fromlist gives the names of objects or submodules that should be imported from the module given by name.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Aug 11, 2015 at 9:45

machine yearning

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5 Comments

Tanky Woo Over a year ago

I have tried __import__/importlib, but can't implment this

machine yearning Over a year ago

Can you explain why you can't implement it?

Tanky Woo Over a year ago

get module by import, and get func by getattr, but func is a variable. It can't implment is the second example

machine yearning Over a year ago

I don't understand what you're saying. Why doesn't it work to use __import__('utils.'+mod_n, fromlist=[func_n])?

Tanky Woo Over a year ago

thank you, I saw the entire __import__ doc and found the usage.

Tanky Woo · Accepted Answer · 2015-08-11 14:07:43Z

0

before I ask the question, I have tried __import__ and importlib, but can't write out the code.

thanks for @machine-yearning, I read the entire doc of __import__.

this is my solution:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import sys
def func_a():
    _func_a()

def func_b():
    _func_b()

if __name__ == '__main__':
    keys = ['func_a']
    for k in keys:
        mod_n = func_n = k
        _temp = __import__('utils.'+mod_n, fromlist=[func_n])
        _func = getattr(_temp, func_n)
        new_func_n = '_{0}'.format(k)
        setattr(sys.modules[__name__], new_func_n, _func)

    func_a()

answered Aug 11, 2015 at 14:07

Tanky Woo

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