Python critique

[Steven D'Aprano]

On Sat, 11 Dec 2010 00:46:41 +0200, Octavian Rasnita wrote:

> How narrow are the scopes in Python?
> Is each block (each level of indentation) a scope? 

Thankfully, no.


> If it is, then I
> think it is very enough because the other cases can be detected easier
> or it might not appear at all in a well-written program.

I don't understand what this means.


> If it is not, then yes, it is a problem.

Why is it a problem?


 
> Can you please tell me how to write the following program in Python?
> 
> my $n = 1;
> 
> {
>   my $n = 2;
>   print "$n\n";
> }
> 
> print "$n\n";
> 
> If this program if ran in Perl, it prints: 
> 2
> 1

Lots of ways. Here's one:


n = 1

class Scope:
    n = 2
    print n

print n



Here's another:

n = 1
print (lambda n=2: n)()
print n



Here's a third:

n = 1

def scope():
    n = 2
    print n

scope()
print n


Here's a fourth:

import sys
n = 1
(sys.stdout.write("%d\n" % n) for n in (2,)).next()
print n


In Python 3, this can be written more simply:

n = 1
[print(n) for n in (2,)]
print n



> I have tried to write it, but I don't know how I can create that block
> because it tells that there is an unexpected indent.

Functions, closures, classes and modules are scopes in Python. If you 
want a new scope, create one of those.



-- 
Steven