Alright, let's dig into why you're hitting this frustrating ImportError even though the certificate_transparency.py file exists right where it should be. Here are the most likely root causes to investigate:

1. Circular Import Loop #

The most common culprit here is a circular import between the __init__.py file you're importing from and the certificate_transparency.py module.

Check the top of /usr/lib/python2.7/site-packages/cryptography/x509/certificate_transparency.py for any imports that reference the parent cryptography.x509 module (like from . import __init__ or from cryptography.x509 import ...). If the certificate_transparency module tries to import something from x509 while x509/__init__.py is still in the process of importing certificate_transparency, it creates a loop that breaks the import process.

2. Python Path & Version Conflicts #

Your pip is installed in a user-local directory (/home/serj/.local/lib/python2.7/site-packages/pip), which means there might be a conflicting version of cryptography installed locally that's taking priority over the system-wide 2.2.2 version you're checking.

Run this command to confirm which cryptography installation Python is actually loading:

python -c "import cryptography; print(cryptography.__file__)"

If the output points to /home/serj/.local/... instead of /usr/lib/..., you've found the conflict. You can either uninstall the local version or use a virtual environment to isolate your dependencies.

3. Corrupted Installation Files #

Even if the .py file exists, the installation might be corrupted—especially since cryptography relies on compiled C extensions that can fail silently during installation.

Try force-reinstalling the exact version to fix any damaged files:

pip install --force-reinstall cryptography==2.2.2

If you run into permission issues with the system-wide directory, add the --user flag to install it to your local pip directory instead.

4. Accidental Name Shadowing #

Double-check your project's root directory and the directory you're running the app from for any files named cryptography.py or x509.py. These would "shadow" the official library modules, causing Python to try importing from your local file instead of the system library.

If you find any such files, rename them immediately (e.g., my_cryptography_utils.py) to avoid the conflict.

5. Python 2.7 Compatibility Quirks #

While cryptography 2.2.2 supports Python 2.7, it's possible that a mismatched dependency version is causing the issue. Additionally, your pip version (10.0.1) is a bit outdated for Python 2.7—try upgrading pip to the latest version supported by Python 2.7 (which is 20.3.4) first:

pip install --upgrade pip==20.3.4

Then re-install cryptography to ensure all dependencies are properly aligned.

内容的提问来源于stack exchange，提问作者serj