I find myself typing import numpy as np almost every single time I fire up the python interpreter. How do I set up the python or ipython interpreter so that numpy is automatically imported?

Use the environment variable PYTHONSTARTUP. From the official documentation:

If this is the name of a readable file, the Python commands in that file are executed before the first prompt is displayed in interactive mode. The file is executed in the same namespace where interactive commands are executed so that objects defined or imported in it can be used without qualification in the interactive session.

So, just create a python script with the import statement and point the environment variable to it. Having said that, remember that ‘Explicit is always better than implicit’, so don’t rely on this behavior for production scripts.

For Ipython, see this tutorial on how to make a ipython_config file

For ipython, there are two ways to achieve this. Both involve ipython’s configuration directory which is located in ~/.ipython.

1. Create a custom ipython profile.
2. Or you can add a startup file to ~/.ipython/profile_default/startup/

For simplicity, I’d use option 2. All you have to do is place a .py or .ipy file in the ~/.ipython/profile_default/startup directory and it will automatically be executed. So you could simple place import numpy as np in a simple file and you’ll have np in the namespace of your ipython prompt.

Option 2 will actually work with a custom profile, but using a custom profile will allow you to change the startup requirements and other configuration based on a particular case. However, if you’d always like np to be available to you then by all means put it in the startup directory.

For more information on ipython configuration. The docs have a much more complete explanation.

I use a ~/.startup.py file like this:

# Ned's .startup.py file
print("(.startup.py)")
import datetime, os, pprint, re, sys, time
print("(imported datetime, os, pprint, re, sys, time)")

pp = pprint.pprint

Then define PYTHONSTARTUP=~/.startup.py, and Python will use it when starting a shell.

The print statements are there so when I start the shell, I get a reminder that it’s in effect, and what has been imported already. The pp shortcut is really handy too…

While creating a custom startup script like ravenac95 suggests is the best general answer for most cases, it won’t work in circumstances where you want to use a from __future__ import X. If you sometimes work in Python 2.x but want to use modern division, there is only one way to do this. Once you create a profile, edit the profile_default (For Ubuntu this is located in ~/.ipython/profile_default) and add something like the following to the bottom:

c.InteractiveShellApp.exec_lines = [
    'from __future__ import division, print_function',
    'import numpy as np',
    'import matplotlib.pyplot as plt',
    ]

As a simpler alternative to the accepted answer, on linux:

just define an alias, e.g. put alias pynp='python -i -c"import numpy as np"' in your ~/.bash_aliases file. You can then invoke python+numpy with pynp, and you can still use just python with python. Python scripts’ behaviour is left untouched.

You can create a normal python script as import_numpy.py or anything you like

#!/bin/env python3
import numpy as np

then launch it with -i flag.

python -i import_numpy.py

Way like this will give you flexibility to choose only modules you want for different projects.

As ravenac95 mentioned in his answer, you can either create a custom profile or modify the default profile. This answer is quick view of Linux commands needed to import numpy as np automatically.

If you want to use a custom profile called numpy, run:

ipython profile create numpy
echo 'import numpy as np' >> $(ipython locate profile numpy)/startup/00_imports.py
ipython --profile=numpy

Or if you want to modify the default profile to always import numpy:

echo 'import numpy as np' >> $(ipython locate profile default)/startup/00_imports.py
ipython

Check out the IPython config tutorial to read more in depth about configuring profiles. See .ipython/profile_default/startup/README to understand how the startup directory works.

My default ipython invocation is

ipython --pylab --nosep --InteractiveShellApp.pylab_import_all=False

--pylab has been a ipython option for some time. It imports numpy and (parts of) matplotlib. I’ve added the --Inter... option so it does not use the * import, since I prefer to use the explicit np.....

This can be a shortcut, alias or script.