How Can I Correctly Import Python Modules from String Variables?

Importing Modules from String Variables with Python's import

In the realm of Python programming, one may encounter the need to import modules dynamically based on string variables. However, this approach can yield unexpected results compared to traditional import statements. In this article, we delve into the inner workings of Python's import function and elucidate the differences between these two approaches.

Consider the following scenario: we wish to obtain a list of main classes from a submodule of thematplotlib library. To do this, we attempt to load the submodule from a string using __import__:

import matplotlib.text as text
x = dir(text)

i = __import__('matplotlib.text')
y = dir(i)

When we compare the lists 'x' and 'y', we discover that 'y' contains unexpected elements not present in 'x'. This suggests that import is loading additional information that we do not require.

The key to understanding this behavior lies in the fromlist parameter of import__. By default, this parameter is an empty list, which instructs __import to load all available attributes from the specified module. To rectify this issue, we need to explicitly specify an empty string ('') in the fromlist:

i = __import__('matplotlib.text', fromlist=[''])
y = dir(i)

With this modification, 'i' now refers exclusively to the 'matplotlib.text' submodule, and 'y' contains the desired list of main classes.

Alternatively, in Python 3.1 or later, we can use the importlib module to achieve the same result:

import importlib

i = importlib.import_module("matplotlib.text")
y = dir(i)

By understanding the complexities of Python's import mechanisms, we can effectively navigate the nuances of module loading and ensure that our programs behave as intended.

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