On 9/27/20 4:42 PM, Christian Gollwitzer wrote:
> Am 26.09.20 um 06:43 schrieb Stephane Tougard:
>> ===PYTHON===
>> #!/usr/local/bin/python
>> if 4 == 4:
>> name = "Stephane"
>> print(name)
>> pass
>>
>> print("Out {}".format(name))
>> ============
>>
>> The exact same code in Python works fine, the variable name is used
>> outside of the if block even it has been declared inside.
>>
>> This does not look right to me.
>
> I'll try another way of explaining it. You seem to be confused that
> the scope of the variable assignment[*] continues after the if.
> However, look at this:
>
> def f():
> a=3
>
> f()
> a
>
> NameError
> Traceback (most recent call last)
> <ipython-input-3-60b725f10c9c> in <module>()
> ----> 1 a
>
> NameError: name 'a' is not defined
>
> So the "def f()" obviously introduces local scope, but control
> structures like if and while do not.
>
> Christian
>
>
> [*] In Python it's called "name binding", but it mostly works like
> variable assignment
Yes, functions and classes have a scope, control structures do not. If
control structures created a scope it would be ugly.
You do need to watch out about the difference between classical
'variables' and pythons name binding when you deal with mutable objects;
For example:
a = []
b = a
a.append(1)
print(b)
give [1] as a and b are bound to the same object, even though you want
to think of them as different variables.
--
Richard Damon
--
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