singledispatch.py

def api(arg):
    if isinstance(arg, (str, bytes)):
        if isinstance(arg, bytes):
            arg = arg.decode('utf8')
        arg = [arg]
    ... # do something
    return arg
    
print(api(b'123')) # -> ['123']

######## Compare and contrast above with below

from functools import singledispatch

@singledispatch
def api(arg):
    ... # do something
    return arg

@api.register(str)
def _(arg):
    return api([arg])

@api.register(bytes)
def _(arg):
    return api(arg.decode('utf8'))
    
print(api(b'123')) # -> ['123']