Python Documentation or reference to CPython source code
tested on current main: 1a9b10e
There are many examples and I picked one.
# the following is True in CPython and False in RustPython
print(
"\u1c89".istitle() == False,
"DZ".title() == "Dz",
"\u0661".isdigit() == True,
"\u0c5d".isidentifier() == True,
"\u3405".isnumeric() == True,
# known issues of isalpha and isalnum omitted
)