Pascal "var parameter" in Python

Question

In Pascal we have var parameters, and functions can change parameter values to new values:

procedure a(var S1, S2: string);
begin
  S1:= S1+'test'+S1;
  S2:= S1+'('+S2+')';
end;

Does Python have such a feature? Can I change the string parameter inside the method, or must I use return and assign the variable later?

Answer 1

Python can return multiple values (in the form of a tuple), obsoleting the need to pass values by reference.

In your simple sample case, even if you were able to apply the same technique, you could not achieve the same result as Python strings are not mutable.

As such, your simple example can be translated to Python as:

def a(s1, s2):
    s1 = '{0}test{0}'.format(s1)
    s2 = '{}({})'.format(s1, s2)
    return s1, s2

foo, bar = a(foo, bar)

The alternative is to pass in mutable objects (dictionaries, lists, etc.) and alter their contents.