Python迭代字典

Question

In [26]: test = {}

In [27]: test["apple"] = "green"

In [28]: test["banana"] = "yellow"

In [29]: test["orange"] = "orange"

In [32]: for fruit, colour in test:
   ....:     print fruit
   ....:     
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
/home1/users/joe.borg/<ipython-input-32-8930fa4ae2ac> in <module>()
----> 1 for fruit, colour in test:
      2     print fruit
      3 

ValueError: too many values to unpack

What I want is to iterate over test and get the key and value together. If I just do a for item in test: I get the key only.

An example of the end goal would be:

for fruit, colour in test:
    print "The fruit %s is the colour %s" % (fruit, colour)

Answer 1

In Python 2 you'd do:

for fruit, color in test.iteritems():
    # do stuff

In Python 3, use items() instead ( iteritems() has been removed):

for fruit, color in test.items():
    # do stuff

This is covered in the tutorial .

Answer 2

Change

for fruit, colour in test:
    print "The fruit %s is the colour %s" % (fruit, colour)

to

for fruit, colour in test.items():
    print "The fruit %s is the colour %s" % (fruit, colour)

or

for fruit, colour in test.iteritems():
    print "The fruit %s is the colour %s" % (fruit, colour)

Normally, if you iterate over a dictionary it will only return a key, so that was the reason it error-ed out saying "Too many values to unpack". Instead items or iteritems would return a list of tuples of key value pair or an iterator to iterate over the key and values .

Alternatively you can always access the value via key as in the following example

for fruit in test:
    print "The fruit %s is the colour %s" % (fruit, test[fruit])

Answer 3

The normal for key in mydict iterates over keys. You want to iterate items:

for fruit, colour in test.iteritems():
    print "The fruit %s is the colour %s" % (fruit, colour)