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Groups > comp.lang.python > #94439

global and loop control variable

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About global declarations, Python Language Ref (PLR) explains:

[https://docs.python.org/3.4/reference/simple_stmts.html#the-global-statement]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Names listed in a global statement must not be used
in the same code block textually preceding that global statement.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



What I understand is that the following code is incorrect:

# ---------------------------------------
def f():
    x=42
    global x

f()
print(x)
# ---------------------------------------

And indeed, executing this piece of code "raises" a warning :

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.py:3: SyntaxWarning: name 'x' is assigned to before global declaration
  global x
42
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Now, global declaration has another restriction, as PLR explains:

[https://docs.python.org/3.4/reference/simple_stmts.html#the-global-statement]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Names listed in a global statement must not be defined as formal parameters
or in a for loop control target, 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

What I understand is that the following is a must-not-code:

# ---------------------------------------
def f():
    global i
    for i in range(1,3):
        print(10*i)

f()
print(i)
# ---------------------------------------

But, the later code executes silently without any warning:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
10
20
2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

So my question is: what is the restriction about global as loop control variable the docs is referring to?

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Thread

global and loop control variable candide <c.candide@laposte.net> - 2015-07-23 03:24 -0700
  Re: global and loop control variable Lorenzo Sutton <lorenzofsutton@gmail.com> - 2015-07-23 13:20 +0200
    Re: global and loop control variable Steven D'Aprano <steve@pearwood.info> - 2015-07-23 22:31 +1000
      Re: global and loop control variable Lorenzo Sutton <lorenzofsutton@gmail.com> - 2015-07-23 15:58 +0200

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