'too many values to unpack', iterating over a dict. key=>string, value=>list

For Python 3.x iteritems has been removed. Use items instead.

for field, possible_values in fields.items():
    print(field, possible_values)

Python 3

Use items().

for field, possible_values in fields.items():
    print(field, possible_values)

Python 2

Use iteritems().

for field, possible_values in fields.iteritems():
    print field, possible_values

---

See this answer for more information on iterating through dictionaries, such as using items(), across Python versions.

For reference, iteritems() was removed in Python 3.

For lists, use enumerate

for field, possible_values in enumerate(fields):
    print(field, possible_values)

iteritems will not work for list objects

You want to use iteritems. This returns an iterator over the dictionary, which gives you a tuple(key, value)

>>> for field, values in fields.iteritems():
...     print field, values
... 
first_names ['foo', 'bar']
last_name ['gravy', 'snowman']

Your problem was that you were looping over fields, which returns the keys of the dictionary.

>>> for field in fields:
...     print field
... 
first_names
last_name