ModuleNotFoundError: No module named 'cryptography'

Not specified by the original author.

ModuleNotFoundError: No module named 'cryptography'

TL;DR: run pip install cryptography. It was probably only a transitive dependency; declare it directly.

ModuleNotFoundError: No module named 'cryptography'

The fix

pip install cryptography

Verify:

python -c "from cryptography.fernet import Fernet; print('ok')"

Expected output: ok.

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

When this applies

• Fresh virtualenvs, containers, or CI runners.
• It worked locally because paramiko or pyOpenSSL pulled it in.
• Minimal Docker images.

When it does NOT apply

• cannot import name 'default_backend', which is a version problem with it installed.
• No module named 'cryptography.hazmat.bindings._rust', which is a broken install.

Why this happens

Nearly everything in Python crypto depends on cryptography, so it feels ubiquitous, but feeling ubiquitous is not being declared. When the package that dragged it in is removed or its extras change, the import breaks. Direct dependencies beat transitive ones.

Compatibility

cryptography 41+ on all supported Pythons. Ships Rust-based wheels; needs no compiler on common platforms.

cryptography underpins paramiko, pyOpenSSL, bcrypt's ecosystem neighbors, and much of Python TLS, yet it is often only a transitive dependency and goes missing in fresh virtualenvs, containers, and CI runners. The PyPI page documents pip install cryptography. The names match here, so this is a missing-requirement problem; the distinctive cryptography failures (defaultbackend, asn1/rust) only happen after it is installed.

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.

Not specified by the original author.

ModuleNotFoundError: No module named 'OpenSSL'

TL;DR: the distribution is called pyOpenSSL but the module is OpenSSL. Run pip install pyOpenSSL and the import works.

ModuleNotFoundError: No module named 'OpenSSL'

The fix

pip install pyOpenSSL

Verify:

python -c "from OpenSSL import SSL; print('ok')"

Expected output: ok.

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

When this applies

• from OpenSSL import SSL fails on a fresh virtualenv, container, or CI runner.
• You ran pip install OpenSSL (no such distribution) or never installed it.
• urllib3 1.x PyOpenSSL injection code that imports OpenSSL.

When it does NOT apply

• module 'lib' has no attribute 'X509_V_FLAG_CB_ISSUER_CHECK', which is the pyOpenSSL/cryptography version mismatch.
• Import errors for _cffi_backend, which is the cffi backend problem.

Why this happens

Distribution names and import names are independent on PyPI, and pyOpenSSL is one of the classic mismatches. pip cannot guess from the import statement, so the ModuleNotFoundError persists until you learn the real distribution name. The PyPI page always lists the exact install command.

Compatibility

pyOpenSSL 23+. Needs the cryptography package, which pip installs automatically.

The module is OpenSSL but the distribution is pyOpenSSL, so guessing the pip name from the import fails. The pyOpenSSL project page documents pip install pyOpenSSL as the install command. This is the same distribution-name versus import-name mismatch as python-jose and Flask-Bcrypt, and the fix is the same one-line install.