> To be fair, I also don't know which of those split on str.split() with no arguments to the method either.
I couldn't resist -- the answer is most of them:
#!/usr/bin/env python
weird_spaces = ("x\u0020x\u00A0x\u1680x\u180Ex\u2000x\u2001x\u2002"
"x\u2003x\u2004x\u2005x\u2006x\u2007x\u2008x\u2009"
"x\u200Ax\u200Bx\u202Fx\u205Fx\u3000x\uFEFFx")
print(weird_spaces)
splitted = weird_spaces.split()
print(splitted)
print(len(weird_spaces))
print(len(splitted))
$ python weird_spaces.py
x x x xx x x x x x x x x x x xx x x xx
['x', 'x', 'x', 'x\u180ex', 'x', 'x', 'x', 'x', 'x', 'x', 'x', 'x', 'x', 'x', 'x\u200bx', 'x', 'x', 'x\ufeffx']
41
18
-CHB