Convert a split string to a tuple results in "too many values to unpack"

Question

Using split in a for loop results in the mentioned exception. But when taking the elements indpendent from a for loop it works:

>>> for k,v in x.split("="):
...   print k,v
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: too many values to unpack
>>> y =  x.split("=")
>>> y
['abc', 'asflskfjla']
>>> k,v = y
>>> k
'abc'
>>> v
'asflskfjla'

An explanation would be appreciated - and also naturally the proper syntax for the for loop version.

Answer 1

The for loop expects that each item in the iterable can be unpacked into two variables. So in your case, it'd look something like one of these:

[('a, b'), ('c, d'), ...]
[['a, b'], ['c, d'], ...]
['ab', 'cd', ...]
...

Each item in each of those iterables can be split up into a k and a v component. In your case, they cannot, as the output of x.split('=') is a list of strings with more than two characters:

['abc', 'asflskfjla']

Answer 2

x.split returns a list of strings, as you can see from your y variable. When you iterate over that, it takes the first element of the list 'abc' and tries to bind it to the tuple k, v. Since strings are a sequence type, it tries to assign the characters of the string to the tuple you've asked for - and there are in fact too many values (three letters) to unpack into a two-element tuple.

Answer 3

If you wanted this behavior just wrap s.split() in a list:

>>> for (k,v) in [s.split("=")]:
    print(k,v)  
('abc', 'asflskfjla')