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

• Wander Nauta: 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.
• PM 2Ring: Take a look at the importlib module.

Answer 1

__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.

• Tanky Woo: I have tried __import__/importlib, but can't implment this
• machine yearning: Can you explain why you can't implement it?
• Tanky Woo: get module by import, and get func by getattr, but func is a variable. It can't implment is the second example
• machine yearning: I don't understand what you're saying. Why doesn't it work to use __import__('utils.'+mod_n, fromlist=[func_n])?
• Tanky Woo: thank you, I saw the entire __import__ doc and found the usage.

Answer 2

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()