Python doesn't have implicit declaration. The first occurrence of the assignment syntax declares the variable and binds it to a value.

Proof that Python doesn't have implicit declaration:

  >>> foo
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  NameError: name 'foo' is not defined

Pyhon's design sin is that it fails to distinguish the binding of a variable from assignment. The programmer cannot locally (i.e. just in that statement alone) express "I expect this statement to be freshly creating a variable, introducing it into the scope, with value 42" and "I expect to be assigning value 42 to a variable which already exists in the scope (or else this should be diagnosed)".

An example of a language actually without declaration is Awk. This helps one-liners be very terse, but hinders large programs.

Proof that awk has implicit declaration in contrast to Python:

  $ awk 'BEGIN { print foo }'

  $

No errors. The shell has implicit declaration:

  $ echo $foo

You turn it off in serious scripts with "set -u" to have it diagnosed.