ValueError: need more than 2 values to unpack in Python 2.6.6

Question

i am getting error: ValueError: need more than 2 values to unpack when i run the unit test now, so 2 failures and one skip now as far as i have read about

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Answer 1

You could write a utility function to make your results uniform:

def do_something2():
    return 1, 2

def do_something3():
    return 1, 2, 3

def do_something5():
    return 1, 2, 3, 4, 5

def uniform_result(*args):
    return args[0], args[1], args[2:]

a, b, c =  uniform_result(*do_something2())
print a, b, c
# 1 2 ()

a, b, c =  uniform_result(*do_something3())
print a, b, c
# 1 2 (3,)

a, b, c =  uniform_result(*do_something5())
print a, b, c
# 1 2 (3, 4, 5)

Answer 2

Instead of unpacking in your assignment:

a, b, c = do_something()

Try assigning the result to a single variable and testing its length:

t = do_something()
# t is now a tuple (or list, or whatever was returned) of results
if len(t) > 2:
    # Can use the third result!
    c = t[2]

Answer 3

So errors is a list that contains items that are tuples of length 2 or 3. You want a way to unpack tuples of varying length in a for-loop. As you have noted, there is no clean way to do this in Python2. Rather than coming up with a clever way of implementing this behavior, I would suggest making sure that your errors list always contains tuples of length of 3. This can be done every time you add an item to errors, or after the fact, like this:

errors = [(x[0], x[1], x[2]) if len(x) == 3 else (x[0], x[1], None) for x in errors]

Or you could make a generator (which goes against my advice of not finding clever way to implement this behavior):

def widen_tuples(iter, width, default=None):
    for item in iter:
        if len(item) < width:
            item = list(item)
            while len(item) < width:
                item.append(default)
            item = tuple(item)
        yield item

Use it like this:

>>> errors = [(1, 2), (1, 2, 3)] 
>>> for a, b, c in widen_tuples(errors, 3):
...     print a, b, c
1 2 None
1 2 3

Answer 4

I suggest complementing the list to the necessary length with the None elements:

data = give_me_list()
(val1, val2, val3) = data + (3 - len(data)) * [None]

3 is the number of the left hand side values. If the list can have excessive elements, then use protection against that:

data = give_me_list()[:3]
(val1, val2, val3) = data + (3 - len(data)) * [None]