ModuleNotFoundError: No module named 'psycopg2'

Not specified by the original author.

How to fix ModuleNotFoundError: No module named 'psycopg2'

SQLAlchemy does not ship a Postgres driver; a bare postgresql:// URL defaults to psycopg2. Install it: pip install psycopg2-binary (no compiler needed), or switch the URL to the v3 driver you do have: postgresql+psycopg://... with pip install "psycopg[binary]". The driver name in the URL must match the installed package.

The exact error

ModuleNotFoundError: No module named 'psycopg2'

Fix it

1. Check which driver you have: python -m pip show psycopg2-binary psycopg. Expected: you see which (if any) is installed

2. Easiest: python -m pip install psycopg2-binary and keep postgresql://. Expected: create_engine connects

3. Or go v3: python -m pip install "psycopg[binary]" and change the URL to postgresql+psycopg://host/db. Expected: connects via psycopg3

When this applies

create_engine('postgresql://...') raises No module named 'psycopg2'

When this does NOT apply

NoSuchModuleError: Can't load plugin for a different dialect (that is a URL/dialect mismatch)

Versions

SQLAlchemy with postgresql:// URLs

Why it happens

DBAPI drivers are separate packages by design; SQLAlchemy only knows the dialect name.

Edge cases

psycopg2 from source needs pg_config/libpq headers to build; psycopg2-binary avoids that. Keep the password in env vars, not code.

Asked about: ModuleNotFoundError: No module named 'psycopg2' (gh:zzstoatzz/plyr.fm#1584). The verified fix: SQLAlchemy does not ship a Postgres driver; a bare postgresql:// URL defaults to psycopg2. Install it: pip install psycopg2-binary (no compiler needed), or switch the URL to the v3 driver you do have: postgresql+psycopg://... with pip install "psycopg[binary]". The driver name in the URL must match the installed package. Full thread: https://github.com/zzstoatzz/plyr.fm/issues/1584

Not specified by the original author.

ModuleNotFoundError: No module named 'keycloak'

TL;DR: the distribution is called python-keycloak, not keycloak. Run pip install python-keycloak and the import works.

ModuleNotFoundError: No module named 'keycloak'

The fix

pip install python-keycloak

Verify:

python -c "from keycloak import KeycloakOpenID; print('ok')"

Expected output: ok.

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

When this applies

• First-time Keycloak integration in Python.
• Fresh virtualenvs, containers, or CI runners.
• You ran pip install keycloak and the import still failed.

When it does NOT apply

• Connection errors to the Keycloak server, which happen after the import works.
• keycloak.exceptions errors, which are runtime API errors, not import errors.

Why this happens

The keycloak name on PyPI does not belong to this project, so the distribution took the python- prefixed name while the module kept the clean one. pip installs exactly what you name; the ModuleNotFoundError persists until you use the real distribution name.

Compatibility

python-keycloak 3.x/4.x/5.x. Works against Keycloak servers 18+; check the compatibility matrix in the docs for older servers.

The module is keycloak but the distribution is python-keycloak, so pip install keycloak does not provide the expected API. The python-keycloak project page documents pip install python-keycloak as the install command. This is the same naming trap as python-jose and python-gnupg, and it bites everyone integrating Keycloak auth into Python for the first time.

Not specified by the original author.

ModuleNotFoundError: No module named 'saml2'

TL;DR: the distribution is called pysaml2. Run pip install pysaml2 and the saml2 imports work.

ModuleNotFoundError: No module named 'saml2'

The fix

pip install pysaml2

Verify:

python -c "from saml2 import BINDING_HTTP_REDIRECT; print('ok')"

Expected output: ok.

Agent? Search Vectle for more: curl -s 'https://vectle.com/api/v1/search?q=pysaml2+No+module+named+saml2'

When this applies

• Code importing from the top-level saml2 package.
• Fresh virtualenvs, Docker builds, or CI runners.
• Choosing between the two Python SAML libraries.

When it does NOT apply

• No module named 'onelogin', which is python3-saml, the other SAML library.
• SAML metadata or binding errors after the import works.

Why this happens

The saml2 name was too generic to claim on PyPI, so the distribution took the py prefix while the module kept the clean name. The quick way to tell the libraries apart: saml2 imports mean pysaml2, onelogin.saml2 imports mean python3-saml.

Compatibility

pysaml2 7.x with Python 3.8+. Needs xmlsec; on minimal Linux images install the system xmlsec libraries first.

The module is saml2 but the distribution is pysaml2, so pip install saml2 does not provide it. The pysaml2 project page documents pip install pysaml2 as the install command. This is the other major Python SAML library alongside python3-saml, and the two are frequently confused: if your code imports saml2, you want pysaml2; if it imports onelogin.saml2, you want python3-saml.