What happens when you import modules in Python

 

I’ve been using Python for a number of years now – but like most things I didn’t really understand this until I investigated it.

Firstly let’s introduce what a module is, this is one of Python’s main abstraction layers, and probably the most natural one.

Abstraction layers allow a programmer to separate code into
parts that hold related data and functionality.

In python you use ‘import’ statements to use modules.

Importing modules

The

[sourcecode language=”python”]import modu[/sourcecode]

statement will look for the definition
of modu in a file called `modu.py` in the same directory as the caller
if a file with that name exists.

If it is not found, the Python interpreter will search for modu.py in `Python’s search path`.

Python search path can be inspected really easily

[sourcecode language=”python”]import sys
`>>> sys.path`[/sourcecode]

Here is mine for a conda env.

[sourcecode language=”bash”][”, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/pymc3-3.0rc1-py3.5.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/numpydoc-0.6.0-py3.5.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/nbsphinx-0.2.9-py3.5.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/Sphinx-1.5a1-py3.5.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/recommonmark-0.4.0-py3.5.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/CommonMark-0.5.4-py3.5.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/tqdm-4.8.4-py3.5.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/joblib-0.10.3.dev0-py3.5.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/pandas-0.19.0rc1-py3.5-macosx-10.6-x86_64.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/Theano-0.8.2-py3.5.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/numpy-1.11.2rc1-py3.5-macosx-10.6-x86_64.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/imagesize-0.7.1-py3.5.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/alabaster-0.7.9-py3.5.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/Babel-2.3.4-py3.5.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/snowballstemmer-1.2.1-py3.5.egg’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python35.zip’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/plat-darwin’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/lib-dynload’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages’, ‘/Users/peadarcoyle/anaconda/envs/py3/lib/python3.5/site-packages/setuptools-27.2.0-py3.5.egg’]

[/sourcecode]

What is a namespace?

We say that the modules variables, functions, and classes will be available
to the caller through the modules `namespace`, a central concept in programming that
is particularly helpful and powerful in Python. Namespaces provide a scope containing
named attributes that are visible to each other but not directly accessible outside of the namespace.

So there you have it this is an explanation of what happens when you import, and what a namespace is.

This is based on the Hitchikers guide which is well worth a read 🙂

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