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

367
votes

I am getting the 'too many values to unpack' error. Any idea how I can fix this?

first_names = ['foo', 'bar']
last_names = ['gravy', 'snowman']

fields = {
    'first_names': first_names,
    'last_name': last_names,
}        

for field, possible_values in fields:  # error happens on this line
9
python

9 Answers

533
votes

Python 2

You need to use something like 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.

Python 3

Since Python 3 iteritems() is no longer supported. Use items() instead.

for field, possible_values in fields.items():
    print(field, possible_values)
87
votes

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

for field, possible_values in fields.items():
    print(field, possible_values)
38
votes

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
13
votes

For lists, use enumerate

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

iteritems will not work for list objects

1
votes

you are missing fields.iteritems() in your code.

You could also do it other way, where you get values using keys in the dictionary.

for key in fields:
    value = fields[key]
0
votes

Can't be iterating directly in dictionary. So you can through converting into tuple.

first_names = ['foo', 'bar']
last_names = ['gravy', 'snowman']

fields = {
    'first_names': first_names,
    'last_name': last_names,
         } 
tup_field=tuple(fields.items())
for names in fields.items():
     field,possible_values = names
     tup_possible_values=tuple(possible_values)
     for pvalue in tup_possible_values:
           print (field + "is" + pvalue)
0
votes

In Python3 iteritems() is no longer supported

Use .items

for field, possible_values in fields.items():
    print(field, possible_values)
0
votes

Just thought I'd throw this in. I have the "too many values to unpack (expected 2)" crop up today. Infuriating but is was due to missing a comma in a choice list.

CapTextureChoices = [
("initial", ""),
("Shaggy", "Shaggy"),
("Wrinkled", "Wrinkled"),
("Striate," "Striate"),
("Downy", "Downy")
]

the missing comma between "Striate," "Striate" was the culprit

-1
votes
data = (['President','George','Bush','is','.'],['O','B-PERSON','I-PERSON','O','O'])
corpus = []
for(doc,tags) in data:
    doc_tag = []
    for word,tag in zip(doc,tags):
        doc_tag.append((word,tag))
        corpus.append(doc_tag)
        print(corpus)