Slow startup on Windows for virtual environments

[paugier (Pierre Augier)]

@JamesParrott

I think conda should be ruled out. I know pip doesn’t work as usual, in a ‘venv’ created with uv (uv pip must be used instead).

I would be much less pessimistic than you about conda installed Pythons. What is bad/dangerous with conda is to mix conda and pip installs. But we’ll see when I am able to install Python from the Microsoft Store…

About UV, I used uv venv and uv pip and it gives the same results. The problem is general and related to how black.exe (a .exe wrapper) and python.exe in the virtual environment are created: by modifying precompiled binaries. Then, something on my PC on Windows delays the startup of the application with security checks. (see About .exe wrappers created by frontends when installing wheels on Windows? - #8 by steve.dower)

@JamesParrott

Otherwise it occurred to me that if the “fast” Python being compared to is installed on an SSD, but the “slow” venvs are being created on an HDD, there would be noticeable delays.

Everything is of course installed on the same disk so it is not that.