As @Ignacio says, you can’t do this. In your latter example, you might have a situation where None
is a valid value for arg2
. If this is the case, you can use a sentinel value:
sentinel = object()
def myfunc(arg1, arg2=sentinel):
if arg2 is sentinel:
arg2 = arg1
print (arg1, arg2)
myfunc("foo") # Prints 'foo foo'
myfunc("foo", None) # Prints 'foo None'