ERROR: Could not build wheels for cryptography which use PEP 517 and cannot be installed directly

Question

I get an error when pip builds wheels for the cryptography package.

Error:

LINK : fatal error LNK1181: cannot open input file 'libssl.lib'
  error: command 'C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\BuildTools\\VC\\Tools\\MSVC\\14.16.27023\\bin\\HostX86\\x86\\link.exe' failed with exit status 1181
  ----------------------------------------
  ERROR: Failed building wheel for cryptography
  Running setup.py clean for cryptography
Failed to build cryptography
ERROR: Could not build wheels for cryptography which use PEP 517 and cannot be installed directly

I have already installed OpenSSL and set the environment variables as suggested in this post yet the problem persists. My setup details:

• System - Windows 10
• Python - 3.8
• Pip - 19.3.1

Answer 1

Setting cryptography to version 2.8 in requirements.txt fixed the issue.

Answer 2

TLDR;

Try using cryptography==3.1.1

Details:

This happened on Python 3.9.0 on Windows 10 PC. I had the following in requirements.txt

cryptography==2.8

I removed the version and kept only cryptography in requirements.txt file like below

cryptography

Saved the requirements.txt and then I ran

pip install -r requirements.txt

It installed successfully. Then I freeze the requirements.txt by running the following command

pip freeze > requirements.txt

Then the requirements.txt got updated with cryptography==3.1.1

Answer 3

In my case (windows 10 + conda) updating pip fixed the problem:

python -m pip install --upgrade pip