Python3 -m /path/to/file is giving me an error, whereas python -m /path/to/file is not


I have been using the mod option on the command line with python (Python 2.7.X) for a while, and I am now switching to Python 3.

python -m path/to/file

Now when I try to do the same procedure, but with Python 3, literally the same line:

python3 -m path/to/file

I am given the following error:

/usr/bin/python3: No module named path/to/file

I have been reading the documentation for both Python 2.X and Python 3.X about the -m option, and I have yet to figure out how the small changes made for 3.X have rendered the above mentioned utilization on my side broken!

Asked By: Castiel



Python3 won’t look for Python2 modules. You need to install modules specifically for Python3.

To give a concrete example: Under Debian, package python-numpy installs to /usr/lib/python2.7/dist-packages/numpy/ whereas package python3-numpy installs to /usr/lib/python3/dist-packages/numpy/. Python2 will only search in /usr/lib/python2.7/dist-packages/; Python3 will only search in /usr/lib/python3/dist-packages/.

Accept this as it is; don’t try to modify the search paths of your local installation, lest you will end in a terrible mess. Rather do reinstall each single module in its Python3 variant.

Answered By: Joachim W

The usage is not:

$ python -m path/to/file

but rather

$ python -m package.subpackage.module

The -m flag adds the current directory to your Python path, then it looks on the Python path for the module to open the program with. For example:

$ cat >
import sys

$ python -m foo
2.7.8 (default, Jul 28 2014, 01:34:03)
[GCC 4.8.3]

$ python -m /foo
/usr/bin/python: No module named /foo

$ python -m ~/foo
/usr/bin/python: No module named /cygdrive/c/Users/user/foo

$ python -m ~/
/usr/bin/python: Import by filename is not supported.
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