Dangerous behavior of list(generator)

[Mel]

exarkun at twistedmatrix.com wrote:
[ ... ]
it's as if a loop like this:
> 
>     for a in b:
>         c
> 
> actually meant this:
> 
>     for a in b:
>         try:
>             c
>         except StopIteration:
>             break
> 
> Note, I know *why* the implementation leads to this behavior.  I'm
> asking why "the devs" *accept* this.

It's part of the price Python pays for letting people get their hands on the 
controls.  Consider also:

Python 2.6.2 (release26-maint, Apr 19 2009, 01:56:41) 
[GCC 4.3.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> class dict2(dict):
...   def __getitem__ (self, key):
...     if key == 'fatal':
...       raise KeyError
... 
>>> d = dict2()
>>> d['fatal'] = 'Hello, world!'
>>> print d['fatal']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in __getitem__
KeyError
>>> 


"KeyError when we just put the item into the dict?"
"Yep."


	Mel.

> 
> Jean-Paul