Krzysztof Żuraw Blog

Python imports validation

September 24, 2017

Recently a colleague from work presented to me a nice pattern. I immediately decided to write about it. This blog post is all about this pattern! Let’s get started!

This pattern is useful when working with python modules. When you import module code inside this file gets executed. All of it. This can lead to a nice way of validation. But what can you validate? For example, if given module is configured properly before starting working with it or maybe you need to tell the user that this module can be used only on Linux.

How does this pattern works? It’s very simple yet effective. Imagine that you have a module called windows_utils:

import platform

if platform.system() != 'Windows':
    raise ImportError('This module works only on Windows')


def some_function():
    print("I'm doing something")

If I’m about to import function from this module I can expect this to happen:

>>> from windows_utils import some_function
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
 in ()
----> 1 from windows_utils import some_function

~/Development/personal-blog-projects/blog_python_import/windows_utils.py in ()
    2
    3 if platform.system() != 'Windows':
----> 4     raise ImportError('This module works only on Windows')
    5
    6

ImportError: This module works only on Windows

As you can see the side effects of such import can be useful! That’s all for today! And special thanks for Maniek!

Tagged with python import validation modules

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