On 22/06/13 12:26, Jim Mooney wrote:
On 21 June 2013 16:56, ALAN GAULD <alan.ga...@btinternet.com> wrote:
if isinstance(dict(),typein):
try: newdict = dict(zip(dl[::2],dl[1::2]))
except TypeError:
raise ValueError("input lists must be an even length")
Not sure why TypeError and ValueError is used. I would have thought
StopIteration but explain your logic on that as I'm unclear. But the
Exception never tripped, either way. I tried different length
iterables in the zip, but it looks like dict knows tostop before it
trip thems. Only next() does raises the exception. Unless I am
confused ;')
It's not dict which is smart in this case, but zip(), which stops when one of
the sequences has run out:
py> zip("abcdefg", "1234", "ABCDEFGHIJKLMN")
[('a', '1', 'A'), ('b', '2', 'B'), ('c', '3', 'C'), ('d', '4', 'D')]
In Python 3, zip is "lazy" and only returns items on request, rather than
"eager" returning them all at once in a list. To get the same result in Python 3, use
list(zip(...)) instead.
If you arrange for dict to see a missing value, it will raise ValueError:
py> dict([('a', 1), ('b', 2), ('c',)])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: dictionary update sequence element #2 has length 1; 2 is required
zippy = zip([1,2],[3,4,5,6,7,8,9])
D = dict(zippy)
D
{1: 3, 2: 4} # dict works fine
next(zippy) # exhausting zippy raises StopIteration
Traceback (most recent call last):
File "<string>", line 301, in runcode
File "<interactive input>", line 1, in <module>
StopIteration
That's because zippy is already exhausted by dict, and once exhausted, it stays
exhausted.
--
Steven
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
http://mail.python.org/mailman/listinfo/tutor
