Proposed patch optimizes utility functions in the urllib.parse module.

$ ./python -m timeit -s "from urllib.parse import splittype" -- "splittype('type:'+'x'*1000)"
Unpatched: 100000 loops, best of 3: 17 usec per loop
Patched:   100000 loops, best of 3: 15 usec per loop

$ ./python -m timeit -s "from urllib.parse import splithost" -- "splithost('//www.example.org:80/foo/bar/baz.html')"
Unpatched: 100000 loops, best of 3: 12.7 usec per loop
Patched:   100000 loops, best of 3: 10.6 usec per loop

$ ./python -m timeit -s "from urllib.parse import splithost" -- "splithost('//www.example.org:80')"
Unpatched: 100000 loops, best of 3: 9.34 usec per loop
Patched:   100000 loops, best of 3: 9.09 usec per loop

$ ./python -m timeit -s "from urllib.parse import splituser" -- "splituser('username:password@example.org:80')"
Unpatched: 100000 loops, best of 3: 8.76 usec per loop
Patched:   100000 loops, best of 3: 3.1 usec per loop

$ ./python -m timeit -s "from urllib.parse import splituser" -- "splituser('example.org:80')"
Unpatched: 100000 loops, best of 3: 5.89 usec per loop
Patched:   100000 loops, best of 3: 1.98 usec per loop

$ ./python -m timeit -s "from urllib.parse import splitpasswd" -- "splitpasswd('username:password')"
Unpatched: 100000 loops, best of 3: 7.38 usec per loop
Patched:   100000 loops, best of 3: 3.08 usec per loop

$ ./python -m timeit -s "from urllib.parse import splitpasswd" -- "splitpasswd('username')"
Unpatched: 100000 loops, best of 3: 5.35 usec per loop
Patched:   100000 loops, best of 3: 1.92 usec per loop

$ ./python -m timeit -s "from urllib.parse import splitnport" -- "splitnport('example.org:80')"
Unpatched: 100000 loops, best of 3: 13.2 usec per loop
Patched:   100000 loops, best of 3: 6.58 usec per loop

$ ./python -m timeit -s "from urllib.parse import splitnport" -- "splitnport('example.org')"
Unpatched: 100000 loops, best of 3: 6.03 usec per loop
Patched:   100000 loops, best of 3: 2.37 usec per loop

$ ./python -m timeit -s "from urllib.parse import splitquery" -- "splitquery('/path?query')"
Unpatched: 100000 loops, best of 3: 8.03 usec per loop
Patched:   100000 loops, best of 3: 3.01 usec per loop

$ ./python -m timeit -s "from urllib.parse import splitquery" -- "splitquery('/path')"
Unpatched: 100000 loops, best of 3: 5.21 usec per loop
Patched:   1000000 loops, best of 3: 1.91 usec per loop

$ ./python -m timeit -s "from urllib.parse import splitvalue" -- "splitvalue('attr=value')"
Unpatched: 100000 loops, best of 3: 7.37 usec per loop
Patched:   100000 loops, best of 3: 2.97 usec per loop

$ ./python -m timeit -s "from urllib.parse import splitvalue" -- "splitvalue('attr')"
Unpatched: 100000 loops, best of 3: 5.13 usec per loop
Patched:   1000000 loops, best of 3: 1.9 usec per loop

This functions are not documented but used in the stdlib and third-party code.