如何通过命令提示符导入python文件？

Question

I am working on project euler and wanted to time all of my code. What I have is directory of files in the form 'problemxxx.py' where xxx is the problem number. Each of these files has a main() function that returns the answer. So I have created a file called run.py, located in the same directory as the problem files. I am able to get the name of the file through command prompt. But when I try to import the problem file, I continue to get ImportError: No module named problem . Below is the code for run.py so far, along with the command prompt used.

# run.py
import sys
problem = sys.argv[1]
import problem         # I have also tired 'from problem import main' w/ same result

# will add timeit functions later, but trying to get this to run first
problem.main()

The command prompts that I have tried are the following: (both of which give the ImportError stated above)

python run.py problem001
python run.py problem001.py

How can I import the function main() from the file problem001.py? Does importing not work with the file name stored as a variable? Is there a better solution than trying to get the file name through command prompt? Let me know if I need to add more information, and thank you for any help!

Answer 1

You can do this by using the __import__() function.

# run.py
import sys
problem = __import__(sys.argv[1], fromlist=["main"])         # I have also tired 'from problem import main' w/ same result
problem.main()

Then if you have problem001.py like this:

def main():
    print "In sub_main"

Calling python run.py problem001 prints:

In sub_main

A cleaner way to do this (instead of the __import__ way) is to use the importlib module. Your run.py needs to changes:

import importlib
problem = importlib.import_module(sys.argv[1])

Alternatives are mentioned in this question .

Answer 2

For sure! You can use __ import_ built-in function like __import__(problem) . However this is not recommended to use, because it is not nice in terms of coding-style. I think if you are using this for testing purposes then you should use unittest module, either way try to avoid these constructions.

Regards

Answer 3

You can use exec() trick:

    import sys
    problem = sys.argv[1] 
    exec('import %s' % problem)
    exec('%s.main()' % problem)