ModuleNotFoundError: No module named

What you see

import requests

print(requests.get("https://example.com").status_code)

Traceback (most recent call last):
  File "/home/me/project/main.py", line 1, in <module>
    import requests
ModuleNotFoundError: No module named 'requests'

What it means

import requests searched every folder on sys.path of the interpreter that is running and found no module called requests. The name in quotes is the module Python looked for.

Most of the time the package is installed, just into another Python. A Mac or Linux machine often has three or four interpreters: the system one, one from Homebrew or python.org, and one inside each virtual environment. Each has its own packages.

Why it happens

• pip and python are different interpreters. pip install requests installed into the Python that pip belongs to, and python3 runs another one.
• The virtual environment is not active, or your editor runs a different interpreter from your terminal. Check the interpreter shown in VS Code or PyCharm's status bar.
• The import name is not the package name. You install one name and import another: beautifulsoup4 is import bs4, pillow is import PIL, opencv-python is import cv2, scikit-learn is import sklearn and pyyaml is import yaml.
• Your own module is not on the path. Running python app/main.py from a different folder, or a sub-package imported without running it as python -m app.main.

How to fix it

Install with the same interpreter that runs the code, by calling pip through it:

python3 -m pip install requests

If you are not sure which interpreter runs your code, ask it:

import sys
print(sys.executable)

For a project, make a virtual environment once and work inside it, so every install lands in the same place:

python3 -m venv .venv
source .venv/bin/activate      # Windows: .venv\Scripts\activate
python -m pip install requests

If pip answers with "externally-managed-environment" instead, your Python refuses system-wide installs on purpose; the virtual environment above is the fix.

How each Python version words it

Run on CPython 3.9.6, 3.10.22, 3.11.17, 3.12.15, 3.13.17, 3.14.9 and 3.15.1, on October 25, 2026.

The message is the same in every version here. ModuleNotFoundError was added in Python 3.6 as a subclass of ImportError, so except ImportError: still catches it.