[voltagedivider]

Isn't that common for all/most languages that don't require explicit typing?

[wruza]

This is a scoping rule, not typing. Scoping is a mechanism of symbol resolution, i.e. what do you mean by `foo` at line N. Is it a local, an argument, a global, or addresses a symbol defined in an enclosing scope? Most languages use explicit local definitions, searching implicit ones in outer scopes bottom-up, ending at the global scope. Python was the first popular non-basic language which made implicit assignments to be local and shadowing and function-scoped:

  global x = 1
  def setx():
    if True:
      x = 2 # completely different x
    print x # prints 2, visible outside of `if`
  setx()
  print x # prints 1

This led to a funny keyword 'nonlocal', because you can't simply ignore scoping and pretend that you're BASIC in any serious program.

(To my opinion, python had a good start, but lost in the woods for no clear reason. It's a movie mutant of a language, which tried to appeal to non-programmers and somehow succeed, and then realized that non-programmers eventually become ones, and it's not hard. Now it's too late to fix this mess. End of opinion.)

[xigoi]

JavaScript (strict mode) doesn't have explicit typing, but it still requires variables to be declared.

[wott]

Same for Perl.

[renox]

Uh? Perl optionally requires you to declare variables, which is a good idea IMHO, no noise for small script and any experimented Perl programmer will have learned that 'use strict' is a really good idea for big scripts..

[samhw]

It would be impossible in any language that requires either explicit typing or some kind of 'let' keyword. (Or, in the fringe case, a language like Go which uses a different operator for initialisation-plus-assignment.)

[voltagedivider]

Exactly. That's why I asked about languages that don't require explicit typing. My point is that it's a feature of many languages rather than a Python idiosyncrasy.

[dragonwriter]

Declaration and explicit typing are logically orthogonal, but few if any languages require typing but not declaration. Lots require declaration but not typing.

[bjoli]

It is common tonall languages that have the same syntax for definitions and mutation.

In Scheme, for example, this is not an issue.