Fixing ModuleNotFoundError: No module named

Troubleshooting / module-not-found-error.html

troubleshootingEnv: Python 3.x, pip, virtual environments (venv)Verified: 2026-10-19

The causes and a diagnosis/fix procedure for Python's most common import error. In most cases it is a mismatch between the interpreter that runs and the one that installed.

"I ran pip install, why does it still say No module named?"

ModuleNotFoundError: No module named 'xxx' is the most common Python error. The good news is that most cases share one cause: the Python that runs the code is not the Python where the package was installed.

Symptom

$ python myscript.py
ModuleNotFoundError: No module named 'requests'

But you definitely ran pip install requests. This is where most people get stuck and start searching.

Causes (most frequent first)

Environment mismatch: a virtual environment is active in one terminal, but you ran a different Python
Never actually installed: pip3 and python3 point to different places (multiple Pythons on the machine)
Relative import issue: inside a package you wrote import x instead of from . import x
No pip at all: some minimal images or freshly created environments lack pip

Diagnose in 30 seconds

These commands show which Python this shell uses and whether the package is present.

# 1) Which Python are we using?
python3 -c "import sys; print(sys.executable)"

# 2) Is the package in this Python?
python3 -c "import importlib.util as u; print(u.find_spec('requests'))"

# 3) Which Python is pip attached to?
python3 -m pip --version

If find_spec returns None, the package really is not in that Python. It is a location problem, not an install problem.

Fix

In projects that use a virtual environment, activate it and run again.

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

Without a virtual environment, install into the exact Python you confirmed above.

python3 -m pip install requests

If pip itself is missing, bootstrap it with python3 -m ensurepip --upgrade, or on Debian/Ubuntu install python3-pip python3-venv.

Habits to avoid

sudo pip install — can damage the system Python; use a virtual environment instead.
Reinstalling blindly on every error — the three diagnosis lines above are faster than reinstalling.
Sharing one virtual environment across projects — a classic source of version conflicts.

Related situations

Inside Docker, the same error means the package was not installed in the image, or a different Python was used at install vs. run time. Check the build log for the actual pip install step.
Hitting this right after scaffolding a framework like FastAPI is usually the environment-mismatch case above.

Sources

stackoverflow ImportError: No module named — Old question, same root cause today
stackoverflow Relative imports and ModuleNotFoundError — Package layout
Official docs Official venv docs — Virtual environments

Verified date indicates freshness. Check applicability conditions for older material.