从for循环中更新外部变量值的最佳方法？(best way to update values of outer-scope variables from within a for-loop?)

 这个问题与我之前的问题有关： python更新外部传递的值来自for循环 。 
 
 来自Perl背景，通过引用传递变量并从子范围内更新值从来没有问题，如下面的for循环示例中所示： 
 
#!/usr/bin/perl
my ($str1,$str2) = ('before','before');
print "before - str1:'$str1', str2:'$str2'\n";

foreach my $str($str1,$str2){$str = 'after'}
print "after - str1:'$str1', str2:'$str2'\n";
 
 我在Python中理解这是不可能的，因为变量是按值而不是按引用导入的 ，我在Python中找到的唯一解决方案到目前为止实现了我所需要的是： 
 
def changeValue(str):
  return 'after'

str1 = 'before'
str2 = 'before'
for s in str1,str2: print s

str1 = changeValue(str1)
str2 = changeValue(str2)
for s in str1,str2: print s
 
 虽然不理想，如果我可以在for-loop中进行函数'changeValue'调用，而不是像上面那样单独调用它们，那就没关系了 - 但是我回到了原来的“无法通过引用传递变量”问题。 
 
 我确信必须有一种简单且不那么复杂的Pythonic方法来实现我追求的目标吗？ 

This question is related to my earlier question here: python update outer passed value from within a for loop.
 
Coming from a Perl background it has never been a problem to pass a variable by reference and update the value from within a child scope as in the for-loop example below:
 
#!/usr/bin/perl
my ($str1,$str2) = ('before','before');
print "before - str1:'$str1', str2:'$str2'\n";

foreach my $str($str1,$str2){$str = 'after'}
print "after - str1:'$str1', str2:'$str2'\n";
 
I understand in Python this is not possible as variables are imported by-value rather than by-reference, the only solution I've found within Python so far which achieves exactly what I need is:
 
def changeValue(str):
  return 'after'

str1 = 'before'
str2 = 'before'
for s in str1,str2: print s

str1 = changeValue(str1)
str2 = changeValue(str2)
for s in str1,str2: print s
 
Although not ideal this would be OK if I could make the function 'changeValue' calls from within a for-loop - rather than calling them individually as above - but then I am back to the original "can't pass a variable by reference" problem. 
 
I am sure that there must be a simple and less convoluted Pythonic way to achieve what I'm after?

原文：https://stackoverflow.com/questions/12303018