What are the differences between dict.items() and dict.iteritems()?

Question

Are there any applicable differences between dict.items() and dict.iteritems()?

From the Python docs:

dict.items(): Return a copy of the dictionary’s list of (key, value) pairs.

dict.iteritems(): Return an iterator over the dictionary’s (key, value) pairs.

If I run the code below, each seems to return a reference to the same object. Are there any subtle differences that I am missing?

a={1:'one',2:'two',3:'three'}

print 'a.items():'

for k,v in a.items():

   if d[k] is v: print '\tthey are the same object'

   else: print '\tthey are different'

print 'a.iteritems():'   

for k,v in a.iteritems():

   if d[k] is v: print '\tthey are the same object'

   else: print '\tthey are different'   

Output-

a.items():

    they are the same object

    they are the same object

    they are the same object

a.iteritems():

    they are the same object

    they are the same object

    they are the same object

Answer 1

dict.items() returns a list of tuples and it is time-consuming and memory exhausting whereas, dict.iteritems() is an iter-generator method which yield tuples and it is less time consuming and less memory exhausting.

In Python 3, some changes were made and now, items() returns iterators and never builds a list fully. Moreover, in this version iteritems() was removed since items() performed the same function like viewitems() in Python 2.7.

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Answer 2

Method dict.items() returns a list of 2-tuples i.e. ([(key, value), (key, value), ...]), whereas dict.iteritems() is a generator that yields 2-tuples. 

In this, the former takes more space and time initially, but accessing each element is fast, whereas the second takes less space and time initially, but a bit more time in generating each element.

Answer 3

You can use the below-mentioned code:

>>> d={1:'one',2:'two',3:'three'}

>>> type(d.items()) 

<type 'list'> 

>>> type(d.iteritems()) 

<type 'dictionary-itemiterator'>