python错误for k,v in d: ValueError: too many values to unpack

John Fouhy john at fouhy.net
Tue May 22 00:50:14 CEST 2007

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On 22/05/07, John Washakie <washakie at gmail.com> wrote:
> I have a Dictionary, that is made up of keys which are email
> addresses, and values which are a list of firstname, lastnamet,
> address, etc...
>
> If I run the following:
>
> last = {}
[...]
> for k,v in last:
>         print "Email: %s , has the Last name: %s" % (k,v[0])
>
> I get the error indicated in the subject:
> ValueError: too many values to unpack

The "implicit" iteration that dictionaries support only iterates over keys.

i.e. you could have done this:

for k in last:
    print "Key is %s, value is %s" % (k, last[k])

Alternatively, you can use the iteritems() method;

for k, v in last.iteritems():
    print "Key is %s, value is %s" % (k, v)

See http://www.python.org/doc/current/lib/typesmapping.html for details.

-- 
John.
简单翻译一下，python只支持对于key的遍历，所以不能使用for k,v这种形式，这个时候会提示ValueError: too many values to unpack，使用粗体的形式代替。