[EDIT: I answered my own question in a comment below, the Python standard library doesn’t seem to have anything important for general programming missing in the Julia ecosystem. If you can think on an exception, please comment.]
Julia supports all the same hardware and operating systems Python does officially support (e.g. Python has additionally “best effort support” for Android, and s390x). Supported platforms and architectures — Unofficial Python Development (Victor's notes) documentation
Python’s standard library is about the most extensive one I can think of, and well you can use all of it (and Python’s external libraries) through PyCall.jl, but I’m curious what they might have that we would want supported natively.
I’m only concerned with modern stuff that needs supporting, file formats and encodings, such as UTF-8 (e.g. not
sunau — Read and write Sun AU files), still what seems missing for Julia (in or out of Julia standard library):
Julia has packages for audio (and video), I’m not sure all platforms are supported, nor e.g. platform-specific stuff like:
msvcrt— Useful routines from the MS VC++ runtime
winreg— Windows registry access
winsound— Sound-playing interface for Windows
I believe Julia has everything that C standard library supplies built-in, and most or all that C++ has built-in or available in packages. It’s not important that Julia has everything C++ (or Python) has in its standard library, because for C++ it’s about cross-compiler support. It’s about having the same capabilities somewhere. My pet peeve is Python has ordered dicts in its standard library (they changed from unordered), otherwise I believe Julia has all the same data structures available as it and C++ have, it’s just e.g. that one comes from a package OrderedCollections.jl.
Most of the stuff C++ has that Julia may not have involves some fairly low-level support, e.g. Thread support library: