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nobinobiru
nobinobiru

Reputation: 792

Python3 import error

I have been confusing Python 3's difference from Python 2 about import.

If I have such a directory like this...

module_test/ ->
  a/hello.py
  lib/mad.py

And I want to import hello module from lib/mad.py

So I wrote code like this..

lib/mad.py

import a.hello

And I call python lib/mad.py ,but it happend ImportError.

I don't know why it happen like this.

Do you have any idea? I want to solve this question.

Sample repository is https://github.com/okamurayasuyuki/module_test/tree/master/lib . ##Thanks in advance.

Upvotes: 1

Views: 5091

Answers (1)

Lucio Paiva
Lucio Paiva

Reputation: 20816

Your problem is that by running mad.py from the module_test directory, you guessed that Python would use your current directory as base for finding module b. To prove that it doesn't work, do the following:

  1. Edit your mad.py script and add the following to the beggining of the script:

    import sys
print(sys.path)
exit()

    This will just print the search path Python uses to find modules you try to import and then exit.

  2. Open the terminal, go to folder /module_test and run the following:

    > python lib/mad.py

    Now you should see the path dumped to the terminal. Note that the first entry in the list is the folder 'module_test/lib' not 'module_test' as you would have thought.

So, how do you solve the problem?

Simple: you just have to tell Python the correct directory it should be using to look for your modules. To do that, you must set the PYTHONPATH enviroment variable:

> export PYTHONPATH=$PYTHONPATH:/path/to/module_test

Now if you try to run your script, it should import a.hello as expected!

PS: You should read the official Python tutorial, specially chapter 6 which explains the concept of modules and packages:

http://docs.python.org/3/tutorial/modules.html

That should give you a basic understading and help you solve your problem.

Upvotes: 2

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