> If you misspell a variable [...], you discover this at run time. Ouch.
CL-USER> (defun square (n) (* nn n)) ;; Ouch! nn isn't defined!
; in: DEFUN SQUARE ; (* NN N) ; ; caught WARNING: ; undefined variable: NN ; ; compilation unit finished ; Undefined variable: ; NN ; caught 1 WARNING condition SQUARE
Technically speaking, the more reflection a language provides, the less correct this becomes. Python code can dynamically inject local variables into stack frames, attributes into objects and so on in more or less silly and probably non-portable ways. So in the end, you end up with pragmatic correctness for mostly sane code. If that's enough for you and your project, go with it.
$ perl -Mstrict -E 'say $foo'
Global symbol "$foo" requires explicit package name at -e line 1.
$ cat err.py
def a():
print b
$ pylint -E err.py
************* Module err
E: 2,8:a: Undefined variable 'b'