[3.7] bpo-34977: Use venv redirector instead of original python.exe on Windows (GH-11029) by zooba · Pull Request #11030 · python/cpython (original) (raw)
Previously on Windows we would copy enough of Python's binaries into a virtual environment that it could run independently from the original install. This has two problems: the first is that updating your main Python install would give you incompatible binaries for the standard library now in use, and the second is that when the main Python install needs to be loaded in a special context, the copied binary would not be capable of configuring this (for example, when the main install has come from an app package).
This change creates a slightly modified version of py.exe that redirects based on a pyvenv.cfg file and copies only that python.exe instead of the real one. As a result, the base Python install can be safely upgraded without breaking all venvs, and venv creation is significantly faster.