ModuleNotFoundError+No+module+named+bcrypt

Not specified by the original author.

ModuleNotFoundError: No module named 'flask_bcrypt'

TL;DR: the pip distribution is called Flask-Bcrypt but the module is flask_bcrypt. Run pip install Flask-Bcrypt and the import works.

ModuleNotFoundError: No module named 'flask_bcrypt'

The fix

pip install Flask-Bcrypt

Verify:

python -c "from flask_bcrypt import Bcrypt; print('ok')"

Expected output: ok.

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

When this applies

• Code does from flask_bcrypt import Bcrypt.
• You ran pip install flask_bcrypt (wrong distribution name) or never installed it.
• A fresh virtualenv, container, or CI runner is missing the package.

When it does NOT apply

• The error is about _bcrypt or DLL loading, which is the compiled-extension problem, not a missing package.
• pip show Flask-Bcrypt already reports it installed; then check you are in the right environment.

Why this happens

PyPI distribution names and Python import names are independent. Flask extensions usually use a CamelCase or dashed distribution name with a snake_case module, and guessing one from the other fails. When in doubt, the PyPI page lists the exact pip install command.

Compatibility

Flask-Bcrypt works with Flask 2.x and 3.x and needs the bcrypt package, which pip pulls in automatically.

Flask-Bcrypt is distributed on PyPI as Flask-Bcrypt but imports as flask_bcrypt, so guessing the pip name from the import name fails. The PyPI project page shows the canonical install command pip install Flask-Bcrypt. The fix is a one-line install, and the same pip-name versus import-name mismatch pattern repeats across Flask-JWT-Extended, Flask-Login and other Flask extensions.

Not specified by the original author.

ModuleNotFoundError: No module named 'bcrypt'

TL;DR: run pip install bcrypt. It was probably only ever a transitive dependency, so add it to your requirements explicitly.

ModuleNotFoundError: No module named 'bcrypt'

The fix

pip install bcrypt

Verify:

python -c "import bcrypt; print(bcrypt.hashpw(b'pw', bcrypt.gensalt())[:7])"

Expected output: a hash prefix like $2b$12$.

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

When this applies

• Fresh virtualenvs, containers, or CI runners.
• passlib or Flask-Bcrypt installed without bcrypt coming along.
• The package worked locally because something else pulled it in.

When it does NOT apply

• DLL load failed while importing _bcrypt, which is the broken-wheel problem.
• password cannot be longer than 72 bytes, which is the 4.1 behavior change.

Why this happens

Transitive dependencies are invisible until the thing that pulled them in is removed or upgraded. bcrypt is the classic case: apps use it through passlib for years, then a fresh install without passlib's bcrypt extra leaves it missing. Depending on it directly is the fix.

Compatibility

bcrypt 4.x on all supported Pythons. Ships wheels for Windows, macOS, and Linux.

bcrypt is one of the most depended-upon password-hashing libraries in Python, pulled in by passlib, Flask-Bcrypt, and countless apps, yet it is frequently absent from fresh virtualenvs, containers, and CI runners because it was only ever a transitive dependency. The PyPI page documents pip install bcrypt. Here the names match, so this is always a missing-requirement problem, not a naming trap.

Not specified by the original author.

ModuleNotFoundError: No module named 'cffi'

TL;DR: run pip install cffi. It usually arrives as a transitive dependency of bcrypt, cryptography, or PyNaCl, so declare it directly.

ModuleNotFoundError: No module named 'cffi'

The fix

pip install cffi

Verify:

python -c "import cffi; print('ok')"

Expected output: ok.

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

When this applies

• Minimal containers or fresh virtualenvs.
• The traceback shows cffi missing under bcrypt, cryptography, or nacl imports.
• Source installs of cffi-based packages without the dependency declared.

When it does NOT apply

• No module named '_cffi_backend', which means cffi is present but its compiled half is broken.
• Build failures compiling cffi from source, which need a compiler, not the package.

Why this happens

cffi is infrastructure: almost nobody imports it directly, so nobody declares it. It arrives transitively until the day it does not, usually in a fresh Docker image. One explicit line in requirements ends the class of failure.

Compatibility

cffi 1.15+ on all supported Pythons. Wheels available everywhere; source builds need libffi headers.

cffi is the foreign-function interface underneath bcrypt, cryptography, and PyNaCl, and it goes missing in minimal containers and fresh virtualenvs where it was only ever transitive. The PyPI page documents pip install cffi. When cffi itself is absent (rather than its backend being broken), the fix is the plain install; the subtler _cffi_backend failure is a different skill.