Does Python have an "or equals" function like ||= in Ruby?

Jon-Eric's answer's is good for dicts, but the title seeks a general equivalent to ruby's ||= operator.

A common way to do something like ||= in Python is

x = x or new_value

dict has setdefault().

So if request.session is a dict:

request.session.setdefault('thing_for_purpose', 5)

Precise answer: No. Python does not have a single built-in operator op that can translate x = x or y into x op y.

But, it almost does. The bitwise or-equals operator (|=) will function as described above if both operands are being treated as booleans, with a caveat. (What's the caveat? Answer is below of course.)

First, the basic demonstration of functionality:

x = Truex    Out[141]: Truex |= Truex    Out[142]: Truex |= Falsex    Out[143]: Truex &= Falsex    Out[144]: Falsex &= Truex    Out[145]: Falsex |= Falsex    Out[146]: Falsex |= Truex   Out[147]: True

The caveat is due python not being strictly-typed, and thus even if the values are being treated as booleans in an expression they will not be short-circuited if given to a bitwise operator. For example, suppose we had a boolean function which clears a list and returns True iff there were elements deleted:

def  my_clear_list(lst):    if not lst:        return False    else:        del lst[:]        return True

Now we can see the short-circuited behavior as so:

x = Truelst = [1, 2, 3]x = x or my_clear_list(lst)print(x, lst)Output: True [1, 2, 3]

However, switching the or to a bitwise or (|) removes the short-circuit, so the function my_clear_list executes.

x = Truelst = [1, 2, 3]x = x | my_clear_list(lst)print(x, lst)Output: True []

Above, x = x | my_clear_list(lst) is equivalent to x |= my_clear_list(lst).