Scoping in Python 'for' loops

user_391126 0
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I'm not asking about Python's scoping rules; I understand generally how scoping works in Python for loops. My question is why the design decisions were made in this way. For example (no pun intended):

for foo in xrange(10):
    bar = 2
print(foo, bar)

The above will print (9,2).

This strikes me as weird: 'foo' is really just controlling the loop, and 'bar' was defined inside the loop. I can understand why it might be necessary for 'bar' to be accessible outside the loop (otherwise, for loops would have very limited functionality). What I don't understand is why it is necessary for the control variable to remain in scope after the loop exits. In my experience, it simply clutters the global namespace and makes it harder to track down errors that would be caught by interpreters in other languages.

scope python
7 Answers

It is a design choice in Python, which often makes some tasks easier than in other languages with the typical block scope behavior.

But oftentimes you would still miss the typical block scopes, because, say, you might have large temporary arrays which should be freed as soon as possible. It could be done by temporary function/class tricks but still there is a neater solution achieved with directly manipulating the interpreter state.

from scoping import scoping
a = 2 

with scoping():
    assert(2 == a)
    a = 3
    b = 4
    scoping.keep('b')
    assert(3 == a) 

assert(2 == a) 
assert(4 == b)

https://github.com/l74d/scoping

user_161894510

If you have a break statement in the loop (and want to use the iteration value later, perhaps to pick back up, index something, or give status), it saves you one line of code and one assignment, so there's a convenience.

user_103317140
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