NameError: name 'os' is not defined in Python

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Borislav Hadzhiev

Last updated: Apr 20, 2022

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NameError: name 'os' is not defined in Python #

The Python "NameError: name 'os' is not defined" occurs when we use the os module without importing it first. To solve the error, import the os module before using it - import os.

nameerror name os is not defined

Here is an example of how the error occurs.

main.py
BASE = '/user' # ⛔️ NameError: name 'os' is not defined print(os.path.join(BASE, 'articles')) print(os.environ['VIRTUAL_ENV_PROMPT'])

To solve the error, we have to import the os module.

main.py
# 👇️ import os module first import os BASE = '/user' # 👇️ /user/articles print(os.path.join(BASE, 'articles')) # 👇️ (venv) print(os.environ['VIRTUAL_ENV_PROMPT'])

Even though the os module is in the Python standard library, we still have to import it before using it.

Make sure you haven't used a capital letter o when importing os because module names are case-sensitive.

Also, make sure you haven't imported os in a nested scope, e.g. a function. Import the module at the top level to be able to use it throughout your code.

An alternative to importing the entire os module is to import only the functions and constants that your code uses.

main.py
from os import path, environ BASE = '/user' # 👇️ /user/articles print(path.join(BASE, 'articles')) # 👇️ (venv) print(environ['VIRTUAL_ENV_PROMPT'])

The example shows how to import the path module and the environ mapping object from the os module.

Instead of accessing the members on the module, e.g. os.environ, we now access them directly.

This should be your preferred approach because it makes your code easier to read.

For example, when we use an import such as import os, it is much harder to see which functions from the os module are being used in the file.

Conversely, when we import specific functions, it is much easier to see which functions from the os module are being used.

The os module provides a portable way of using operating system dependent functionality.

You can view all of the functions and constants the os module provides by visiting the official docs.

Conclusion #

The Python "NameError: name 'os' is not defined" occurs when we use the os module without importing it first. To solve the error, import the os module before using it - import os.

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