[FIXED] Why is python mangling here

Issue

Why does this code fail if there is no cls. before __TEXT

__TEXT = "abcde"

print(__TEXT)
class aaa():
    @classmethod
    def bbb(cls):
        print(__TEXT)

aaa.bbb()

The output is:

abcde
Traceback (most recent call last):
  File "<string>", line 9, in <module>
  File "<string>", line 7, in bbb
NameError: name '_aaa__TEXT' is not defined

If you make __TEXT a class variable and try to reference it without the class prefix as follows:

class aaa():
    __TEXT = "abcde"
    @classmethod
    def bbb(cls):
        print(cls.__TEXT)
        print(__TEXT)

x = aaa()
x.bbb()

You get the same error but it doesn't make sense:

abcde
Traceback (most recent call last):
  File "<string>", line 10, in <module>
  File "<string>", line 7, in bbb
NameError: name '_aaa__TEXT' is not defined

Solution

In PEP 8, they specifically say:

__double_leading_underscore: when naming a class attribute, invokes name mangling (inside class FooBar, __boo becomes _FooBar__boo ...).

Notice the selection in bold. In the exact same sentence where they draw attention to mangling's use in naming class attributes, they state that the mangling happens to any __boo inside of the class, which perfectly explains what you are observing.

Answered By - Kraigolas

Answer Checked By - Robin (PHPFixing Admin)