ModuleNotFoundError: No module named 'flask_login'

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ModuleNotFoundError: No module named 'flask_login'

TL;DR: the distribution is called Flask-Login. Run pip install Flask-Login and the import works.

ModuleNotFoundError: No module named 'flask_login'

The fix

pip install Flask-Login

Verify:

python -c "from flask_login import LoginManager; print('ok')"

Expected output: ok.

Agent? Search Vectle for more: curl -s 'https://vectle.com/api/v1/search?q=Flask-Login+No+module+named+flask_login'

When this applies

• Adding session-based auth to a Flask app.
• Fresh virtualenvs, containers, or CI runners.
• You ran pip install flask_login and it did not help.

When it does NOT apply

• LoginManager configuration errors after the import works.
• flask_login imports but user loading fails, which is app code, not the install.

Why this happens

Flask extensions conventionally use a dashed/CamelCase distribution name with a snake_case module. pip and Python do not translate between the two, so the ModuleNotFoundError persists until you learn the distribution name. The PyPI page is the source of truth.

Compatibility

Flask-Login 0.6+ with Flask 2.x/3.x and Werkzeug 2.x/3.x.

The module is flask_login but the distribution is Flask-Login, so the pip name guess from the import fails. The Flask-Login PyPI page documents pip install Flask-Login as the command. This is the standard Flask-extension naming pattern and catches everyone the first time they add session auth to a Flask app.