I have no objection to *deliberate* invocations of the system RNG blocking if needed. Presumably this behavior can be codified into the various APIs.

My objection is *entirely* to _PyRandom_Init() calling a potentially-blocking RNG source, before script parsing even begins. This basically prohibits Python from starting on systems where the system RNG is blocking. Linux is the only affected system *now* because the systemd crontab generator is the only Python script called before the RNG has initialized. Exactly the same issue would apply to any of the BSDs or Solaris, if /dev/urandom blocks as you describe. I want to be clear - this is not a Linux-specific issue.