import win32gui, win32con, os

filter='Python Scripts\0*.py;*.pyw;*.pys\0Text files\0*.txt\0'
customfilter='Other file types\0*.*\0'

fname, customfilter, flags=win32gui.GetSaveFileNameW(
    InitialDir=os.environ['temp'],
    Flags=win32con.OFN_ALLOWMULTISELECT|win32con.OFN_EXPLORER,
    File='somefilename', DefExt='py',
    Title='GetSaveFileNameW',
    Filter=filter,
    CustomFilter=customfilter,
    FilterIndex=1)

print('save file names:', repr(fname))
print('filter used:', repr(customfilter))
print('Flags:', flags)
for k,v in list(win32con.__dict__.items()):
    if k.startswith('OFN_') and flags & v:
        print('\t'+k)

fname, customfilter, flags=win32gui.GetOpenFileNameW(
    InitialDir=os.environ['temp'],
    Flags=win32con.OFN_ALLOWMULTISELECT|win32con.OFN_EXPLORER,
    File='somefilename', DefExt='py',
    Title='GetOpenFileNameW',
    Filter=filter,
    CustomFilter=customfilter,
    FilterIndex=0)

print('open file names:', repr(fname))
print('filter used:', repr(customfilter))
print('Flags:', flags)
for k,v in list(win32con.__dict__.items()):
    if k.startswith('OFN_') and flags & v:
        print('\t'+k)