django error 'too many values to unpack'

问题

I'm learning Django by building a simple recipes app. I have a 1 table model using the 'choices' field option for recipe categories rather than using a 2nd 'categories' table and a foreign key relationship. So i created db table via syncdb and then loaded table with test data. When i go to admin and click on the 'Recipes' link in an attempt to view recipes i get the following error:

Template error

In template /var/lib/python-support/python2.6/django/contrib/admin/templates/admin/change_list.html, error at line 34
Caught an exception while rendering: too many values to unpack

If anyone can shed light on this cryptic error that would be great. Db is Sqlite. Django version is 1.0. The model is listed below:

from django.db import models

class Recipe(models.Model):
    CATEGORY_CHOICES = (
        (1, u'Appetizer'),
        (2, u'Bread'),
        (3, u'Dessert'),
        (4, u'Drinks'),
        (5, u'Main Course'),
        (6, u'Salad'),
        (7, u'Side Dish'),
        (8, u'Soup'),
        (9, u'Sauce/Marinade'),
        (10, u'Other'),        
    )
    name = models.CharField(max_length=255)
    submitter = models.CharField(max_length=40)
    date = models.DateTimeField()
    category = models.SmallIntegerField(choices=CATEGORY_CHOICES)
    ingredients = models.TextField()
    directions = models.TextField()
    comments = models.TextField(null=True, blank=True)

回答1:

Edit: Updated in light of kibibu's correction.

I have encountered what I believe is this same error, producing the message:

Caught ValueError while rendering: too many values to unpack

My form class was as follows:

class CalcForm(forms.Form):
    item = forms.ChoiceField(choices=(('17815', '17816')))

Note that my choices type here a tuple. Django official documentation reads as follows for the choices arg:

An iterable (e.g., a list or tuple) of 2-tuples to use as choices for this field. This argument accepts the same formats as the choices argument to a model field.

src: https://docs.djangoproject.com/en/1.3/ref/forms/fields/#django.forms.ChoiceField.choices

This problem was solved by my observing the documentation and using a list of tuples:

class CalcForm(forms.Form):
    item = forms.ChoiceField(choices=[('17815', '17816')])

Do note that while the docs state any iterable of the correct form can be used, a tuple of 2-tuples did not work:

item = forms.ChoiceField(choices=(('17815', '17816'), ('123', '456')))

This produced the same error as before.

Lesson: bugs happen.

回答2:

You should use a ChoiceField instead of SmallIntegerField

回答3:

If I had to guess, it's because whatever is in the administrative template expects a list of tuples, but you've instead supplied a tuple of tuples (hence the "too many values"). Try replacing with a list instead:

CATEGORY_CHOICES = [    # Note square brackets.
    (1, u'Appetizer'),
    (2, u'Bread'),
    (3, u'Dessert'),
    (4, u'Drinks'),
    (5, u'Main Course'),
    (6, u'Salad'),
    (7, u'Side Dish'),
    (8, u'Soup'),
    (9, u'Sauce/Marinade'),
    (10, u'Other'),        
]

回答4:

Per http://code.djangoproject.com/ticket/972 , you need to move the assignment CATEGORY_CHOICES = ... outside the class statement.

回答5:

I got it working. Most of the 'too many values to unpack' errors that i came across while googling were Value Error types. My error was a Template Syntax type. To load my recipe table i had imported a csv file. I was thinking maybe there was a problem somewhere in the data that sqlite allowed on import. So i deleted all data and then added 2 recipes manually via django admin form. The list of recipes loaded after that.

thanks.

回答6:

I just had the same problem... my cvs file came from ms excel and the date fields gotten the wrong format at saving time. I change the format to something like '2010-05-04 13:05:46.790454' (excel gave me 5/5/2010 10:05:47) and voilaaaa no more 'too many values to unpack’

回答7:

kibibu's comment to Kreychek's answer is correct. This isn't a Django issue but rather an interesting aspect of Python. To summarize:

In Python, round parentheses are used for both order of operations and tuples. So:

foo = (2+2)

will result in foo being 4, not a tuple who's first and only element is 4: 4

foo = (2+2, 3+3)

will result in foo being a two-dimensional tuple: (4,6)

To tell Python that you want to create a one-dimensional tuple instead of just denoting the order of operations, use a trailing comma:

foo = (2+2,)

will result in foo being a one-dimensional tuple who's first and only element is 4: (4,)

So for your scenario:

class CalcForm(forms.Form):
    item = forms.ChoiceField(choices=(('17815', '17816'),))

would give what you want. Using a list is a great solution too (more Pythonic in my opinion), but hopefully this answer is informative since this can come up in other cases.

For example:

print("foo: %s" % (foo))

may give an error if foo is an iterable, but:

print("foo: %s" % (foo,))

or:

print("foo: %s" % [foo])

will properly convert foo to a string whether it's an iterable or not.

Documentation: http://docs.python.org/2/tutorial/datastructures.html#tuples-and-sequences

回答8:

This error IMO occurs when a function returns three values, and you assign it to 2. e.g.:

def test():
    a=0
    b=0
    c=0
.... 
a,b=test() <---three values returned, but only assigning to 2.

a,b,c=test() <---three values returned, assigned to 3.OK

来源：https://stackoverflow.com/questions/913590/django-error-too-many-values-to-unpack

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python

django

sqlite