psf/requests · warning · RequestsDependencyWarning

Unable to find acceptable character detection dependency (ch

Error message

Unable to find acceptable character detection dependency (chardet or charset_normalizer).

What it means

A `RequestsDependencyWarning` (not an exception) emitted at import time from `check_compatibility()` in `src/requests/__init__.py:92`. Requests uses chardet or charset_normalizer to guess a response's text encoding when the server doesn't declare one; if neither package is importable (or their versions fell outside the supported ranges checked just above), it warns that automatic character detection is unavailable. Requests still works — `response.text` just falls back to less accurate encoding handling for undeclared charsets.

Source

Thrown at src/requests/__init__.py:92

    major, minor, patch = int(major), int(minor), int(patch)
    # urllib3 >= 1.21.1
    assert major >= 1
    if major == 1:
        assert minor >= 21

    # Check charset_normalizer for compatibility.
    if chardet_version:
        major, minor, patch = chardet_version.split(".")[:3]
        major, minor, patch = int(major), int(minor), int(patch)
        # chardet_version >= 3.0.2, < 8.0.0
        assert (3, 0, 2) <= (major, minor, patch) < (8, 0, 0)
    elif charset_normalizer_version:
        major, minor, patch = charset_normalizer_version.split(".")[:3]
        major, minor, patch = int(major), int(minor), int(patch)
        # charset_normalizer >= 2.0.0 < 4.0.0
        assert (2, 0, 0) <= (major, minor, patch) < (4, 0, 0)
    else:
        warnings.warn(
            "Unable to find acceptable character detection dependency "
            "(chardet or charset_normalizer).",
            RequestsDependencyWarning,
        )


def _check_cryptography(cryptography_version: str) -> None:
    # cryptography < 1.3.4
    try:
        cryptography_version_list = list(map(int, cryptography_version.split(".")))
    except ValueError:
        return

    if cryptography_version_list < [1, 3, 4]:
        warning = f"Old version of cryptography ({cryptography_version_list}) may cause slowdown."
        warnings.warn(warning, RequestsDependencyWarning)

View on GitHub ↗ (pinned to 414f0513c3)

Solutions

1. Install the standard dependency: `pip install charset_normalizer` (or `pip install 'requests[use_chardet_on_py3]'` for chardet).
2. Reinstall requests with dependencies: `pip install --force-reinstall requests` (drop any `--no-deps` flag in your build).
3. Verify the active interpreter matches where you installed: `python -m pip show charset_normalizer`.
4. If you always know your responses' encodings, you may suppress the warning and set `response.encoding` explicitly — detection is only needed for undeclared charsets.

Example fix

# before (Dockerfile)
RUN pip install --no-deps requests
# after
RUN pip install requests  # pulls charset_normalizer, urllib3, idna, certifi

import importlib.util
if not (importlib.util.find_spec('charset_normalizer') or importlib.util.find_spec('chardet')):
    raise RuntimeError('Install charset_normalizer (or chardet): pip install charset_normalizer')

try:
    import requests
except ImportError as e:
    if 'charset' in str(e) or 'chardet' in str(e):
        sys.exit('Missing charset detection dep — pip install "requests[use_chardet_on_py3]" or charset_normalizer')
    raise

When it happens

Trigger: `import requests` in an environment where neither `charset_normalizer` (>=2,<4) nor `chardet` (>=3.0.2,<8) is installed — the versions are passed into `check_compatibility()` as None when import failed.

Common situations: Minimal/vendored installs, `pip install --no-deps requests`, aggressive dependency pruning in Docker images or lambda bundles, a broken/partial upgrade that uninstalled charset_normalizer, conda/pip mixed environments where the package landed in a different site-packages, or PyInstaller/py2exe bundles that missed the hidden import.

Related errors

• Invalid percent-escape sequence: '{h}'
• Old version of cryptography ({cryptography_version_list}) ma
• Files must be provided.
• Data must not be a string.
• Unsupported event specified, with event name "{event}"

AI-assisted analysis of psf/requests@414f0513c3 (2026-07-31). Data as JSON: /data/errors/5916d25c56cfa39a.json. Report an issue: GitHub ↗.