When should iteritems be used instead of items

Question

Is it legitimate to use items   instead of iteritems   in all places  Why was iteritems   removed from Python 3  Seems like a terrific and useful method  What s the reasoning behind it   Edit  To clarify  I want to know what is the correct idiom for iterating over a dictionary in a generator-like way  one item at a time  not all into memory  in a way that is compatible with both Python 2 and Python 3

User · Accepted Answer

In Python 2 x -  items   returned a list of  key  value  pairs  In Python 3 x   items   is now an itemview object  which behaves different - so it has to be iterated over  or materialised    So  list dict items    is required for what was dict items   in Python 2 x   Python 2 7 also has a bit of a back-port for key handling  in that you have viewkeys  viewitems and viewvalues methods  the most useful being viewkeys which behaves more like a set  which you d expect from a dict    Simple example   common keys   list dict a viewkeys    amp  dict b viewkeys      Will give you a list of the common keys  but again  in Python 3 x - just use  keys   instead   Python 3 x has generally been made to be more  lazy  - i e  map is now effectively itertools imap  zip is itertools izip  etc

User · Answer

You cannot use items instead iteritems in all places in Python  For example  the following code   class C    def   init   self  a       self a   a   def   iter   self       return self a iteritems     gt  gt  gt  c   C dict a 1  b 2  c 3    gt  gt  gt   v for v in c     a   1     c   3     b   2     will break if you use items   class D    def   init   self  a       self a   a   def   iter   self       return self a items     gt  gt  gt  d   D dict a 1  b 2  c 3    gt  gt  gt   v for v in d  Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError    iter   returned non-iterator of type  list    The same is true for viewitems  which is available in Python 3   Also  since items returns a copy of the dictionary   s list of  key  value  pairs  it is less efficient  unless you want to create a copy anyway   In Python 2  it is best to use iteritems for iteration  The 2to3 tool can replace it with items if you ever decide to upgrade to Python 3

User · Answer

Just as  Wessie noted  dict iteritems  dict iterkeys and dict itervalues  which return an iterator in Python2 x  as well as dict viewitems  dict viewkeys and dict viewvalues  which return view objects in Python2 x  were all removed in Python3 x  And dict items  dict keys and dict values used to return a copy of the dictionary s list in Python2 x now return view objects in Python3 x  but they are still not the same as iterator   If you want to return an iterator in Python3 x  use iter dictview       python3 3   gt  gt  gt  d     one   1    two   2    gt  gt  gt  type d items     lt class  dict items  gt   gt  gt  gt   gt  gt  gt  type d keys     lt class  dict keys  gt   gt  gt  gt   gt  gt  gt   gt  gt  gt  ii   iter d items     gt  gt  gt  type ii   lt class  dict itemiterator  gt   gt  gt  gt   gt  gt  gt  ik   iter d keys     gt  gt  gt  type ik   lt class  dict keyiterator  gt

User · Answer

future utils allows for python 2 and 3 compatibility    Python 2 and 3  option 3 from future utils import iteritems heights     man   185  lady   165  for  key  value  in iteritems heights       print key value    gt  gt  gt    lady   165   gt  gt  gt    man   185   See this link  https   python-future org compatible idioms html

User · Answer

dict iteritems was removed because dict items now does the thing dict iteritems did in python 2 x and even improved it a bit by making it an itemview

User · Answer

The six library helps with writing code that is compatible with both python 2 5  and python 3  It has an iteritems method that will work in both python 2 and 3  Example   import six  d   dict  foo 1  bar 2    for k  v in six iteritems d       print k  v

User · Answer

As the dictionary documentation for python 2 and python 3 would tell you  in python 2 items returns a list  while iteritems returns a iterator   In python 3  items returns a view  which is pretty much the same as an iterator   If you are using python 2  you may want to user iteritems if you are dealing with large dictionaries and all you want to do is iterate over the items  not necessarily copy them to a list

[python] When should iteritems() be used instead of items()?

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