Short description of the scoping rules?

Actually, a concise rule for Python Scope resolution, from Learning Python, 3rd. Ed.. (These rules are specific to variable names, not attributes. If you reference it without a period, these rules apply.)

LEGB Rule

• Local — Names assigned in any way within a function (def or lambda), and not declared global in that function

• Enclosing-function — Names assigned in the local scope of any and all statically enclosing functions (def or lambda), from inner to outer

• Global (module) — Names assigned at the top-level of a module file, or by executing a global statement in a def within the file

• Built-in (Python) — Names preassigned in the built-in names module: open, range, SyntaxError, etc

So, in the case of

code1
class Foo:
    code2
    def spam():
        code3
        for code4:
            code5
            x()

The for loop does not have its own namespace. In LEGB order, the scopes would be

• L: Local in def spam (in code3, code4, and code5)
• E: Any enclosing functions (if the whole example were in another def)
• G: Were there any x declared globally in the module (in code1)?
• B: Any builtin x in Python.

x will never be found in code2 (even in cases where you might expect it would, see Antti’s answer or here).