-w, --windows         print Windows form of NAMEs (C:WINNT)

[cfati@cfati-5510-0:/cygdrive/e/Work/Dev/StackOverflow/q054237800]> cygpath.exe -w /cygdrive/c/location/of/file.html
C:locationoffile.html

>>> import subprocess
>>>
>>>
>>> def get_win_path(cyg_path):
...     p = subprocess.Popen(["cygpath", "-w", cyg_path], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
...     o, _ = p.communicate()
...     return o.strip(b"n").decode()
...
>>>
>>> print(get_win_path("/cygdrive/c/location/of/file.html"))
C:locationoffile.html