replace-walrus-operator.md

replace-walrus-operator

The walrus-operator := allows to set local variable from an expression contexts. That is a generalized function that works everywhere and could potententionally replace the normal let-statement a = 1.

In reality however, the walrus-operator is only used in condition-expressions of "if" and "while". Especially for the "while"-case it saves a lot of lines to be written in the source code - and it much more readable. That makes it to creep into source code all the while even that it did not exist before python 3.8

The transformer is limited to the special case of defining a variable in a condition-expression and to evaluate the value right away. Only the conditions of "if" and "while" are checked.

    # original
    def foo(b):
        while (x := int(b)) is not None:
            b += y
        return 0

    # transformed
    def foo(b):
        while True:
            x = int(b)
            if x is not None:
                b += y
            else:
                break
        return 0

and the more simpler if-block

    # original
    if x := fu(): pass

    # transformed
    x = fu()
    if x: pass