When does “pip install” build a wheel?

Question

I found that in different folders, sometimes pip install will build wheel which takes a lot of time, while sometimes it doesn\'t. I\'m not sure why and how to c

Answer 1

Today I encountered a problem where a package wasn't being installed properly because it turns out that its build process generates incorrect wheel packages, even though direct installation works just fine.

I did a bit of poking around, and it turns out that as of now (pip == 8.1.2), there isn't a direct way to control whether or not pip will try to build a wheel out of a given package. I found the relevant source code, and apparently, the wheel build process is used if and only if:

• the wheel module is importable
• a cache directory is in use

As a result of that logic, one can indirectly disable pip's use of wheel-based builds by passing --no-cache-dir on the install command line.