What is the difference 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?

#!/usr/bin/python

d={1:'one',2:'two',3:'three'}
print 'd.items():'
for k,v in d.items():
   if d[k] is v: print '\tthey are the same object' 
   else: print '\tthey are different'

print 'd.iteritems():'   
for k,v in d.iteritems():
   if d[k] is v: print '\tthey are the same object' 
   else: print '\tthey are different'   

Output:

d.items():
    they are the same object
    they are the same object
    they are the same object
d.iteritems():
    they are the same object
    they are the same object
    they are the same object
1
651
4/20/2019 12:34:08 PM

Accepted Answer

It's part of an evolution.

Originally, Python items() built a real list of tuples and returned that. That could potentially take a lot of extra memory.

Then, generators were introduced to the language in general, and that method was reimplemented as an iterator-generator method named iteritems(). The original remains for backwards compatibility.

One of Python 3’s changes is that items() now return iterators, and a list is never fully built. The iteritems() method is also gone, since items() in Python 3 works like viewitems() in Python 2.7.

799
7/26/2016 11:36:26 PM

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


Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Icon