Suppose I have a python function that takes two arguments, but I want the second arg to be optional, with the default being whatever was passed as the first argument. So, I want to do something like this:
def myfunc(arg1, arg2=arg1):
print (arg1, arg2)
Except that doesn't work. The only workaround I can think of is this:
def myfunc(arg1, arg2=None):
if arg2 is None:
arg2 = arg1
print (arg1, arg2)
Is there a better way to do this?
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'