In Python how do I iterate over a dictionary in sorted key order

Question

There s an existing function that ends in the following  where d is a dictionary   return d iteritems     that returns an unsorted iterator for a given dictionary  I would like to return an iterator that goes through the items sorted by key  How do I do that

User · Accepted Answer

Haven t tested this very extensively  but works in Python 2 5 2    gt  gt  gt  d     x  2   h  15   a  2222   gt  gt  gt  it   iter sorted d iteritems      gt  gt  gt  it next     a   2222   gt  gt  gt  it next     h   15   gt  gt  gt  it next     x   2   gt  gt  gt    If you are used to doing for key  value in d iteritems        instead of iterators  this will still work with the solution above   gt  gt  gt  d     x  2   h  15   a  2222   gt  gt  gt  for key  value in sorted d iteritems      gt  gt  gt      print key  value    a   2222    h   15    x   2   gt  gt  gt    With Python 3 x  use d items   instead of d iteritems   to return an iterator

User · Answer

You can now use OrderedDict in Python 2 7 as well    gt  gt  gt  from collections import OrderedDict  gt  gt  gt  d   OrderedDict    first   1                          second   2                          third   3     gt  gt  gt  d items      first   1     second   2     third   3     Here you have the what s new page for 2 7 version and the OrderedDict API

User · Answer

If you want to sort by the order that items were inserted instead of of the order of the keys  you should have a look to Python s collections OrderedDict   Python 3 only

User · Answer

A dict s keys are stored in a hashtable so that is their  natural order   i e  psuedo-random  Any other ordering is a concept of the consumer of the dict   sorted   always returns a list  not a dict  If you pass it a dict items    which produces a list of tuples   it will return a list of tuples   k1 v1    k2 v2        which can be used in a loop in a way very much like a dict  but it is not in anyway a dict   foo          a      1       b      2       c      3         print foo  gt  gt  gt    a   1   c   3   b   2   print foo items    gt  gt  gt     a   1     c   3     b   2    print sorted foo items     gt  gt  gt     a   1     b   2     c   3     The following feels like a dict in a loop  but it s not  it s a list of tuples being unpacked into k v   for k v in sorted foo items         print k  v   Roughly equivalent to   for k in sorted foo keys         print k  foo k

User · Answer

You can now use OrderedDict in Python 2 7 as well    gt  gt  gt  from collections import OrderedDict  gt  gt  gt  d   OrderedDict    first   1                          second   2                          third   3     gt  gt  gt  d items      first   1     second   2     third   3     Here you have the what s new page for 2 7 version and the OrderedDict API

User · Answer

Greg s answer is right  Note that in Python 3 0 you ll have to do   sorted dict items      as iteritems will be gone

User · Answer

sorted returns a list  hence your error when you try to iterate over it  but because you can t order a dict you will have to deal with a list   I have no idea what the larger context of your code is  but you could try adding an iterator to the resulting list   like this maybe    return iter sorted dict iteritems       of course you will be getting back tuples now because sorted turned your dict into a list of tuples  ex   say your dict was     a  1  c  3  b  2  sorted turns it into a list      a  1    b  2    c  3     so when you actually iterate over the list you get back  in this example  a tuple composed of a string and an integer  but at least you will be able to iterate over it

User · Answer

Greg s answer is right  Note that in Python 3 0 you ll have to do   sorted dict items      as iteritems will be gone

User · Answer

Greg s answer is right  Note that in Python 3 0 you ll have to do   sorted dict items      as iteritems will be gone

User · Answer

Use the sorted   function   return sorted dict iteritems      If you want an actual iterator over the sorted results  since sorted   returns a list  use   return iter sorted dict iteritems

User · Answer

In general  one may sort a dict like so   for k in sorted d       print k  d k    For the specific case in the question  having a  drop in replacement  for d iteritems    add a function like   def sortdict d    opts           opts so any currently supported sorted   options can be passed     for k in sorted d    opts           yield k  d k    and so the ending line changes from  return dict iteritems     to  return sortdict dict    or  return sortdict dict  reverse   True

User · Answer

Use the sorted   function   return sorted dict iteritems      If you want an actual iterator over the sorted results  since sorted   returns a list  use   return iter sorted dict iteritems

User · Answer

A dict s keys are stored in a hashtable so that is their  natural order   i e  psuedo-random  Any other ordering is a concept of the consumer of the dict   sorted   always returns a list  not a dict  If you pass it a dict items    which produces a list of tuples   it will return a list of tuples   k1 v1    k2 v2        which can be used in a loop in a way very much like a dict  but it is not in anyway a dict   foo          a      1       b      2       c      3         print foo  gt  gt  gt    a   1   c   3   b   2   print foo items    gt  gt  gt     a   1     c   3     b   2    print sorted foo items     gt  gt  gt     a   1     b   2     c   3     The following feels like a dict in a loop  but it s not  it s a list of tuples being unpacked into k v   for k v in sorted foo items         print k  v   Roughly equivalent to   for k in sorted foo keys         print k  foo k

User · Answer

Assuming you are using CPython 2 x and have a large dictionary mydict  then using sorted mydict  is going to be slow because sorted builds a sorted list of the keys of mydict   In that case you might want to look at my ordereddict package which includes a C implementation of sorteddict in C  Especially if you have to go over the sorted list of keys multiple times at different stages  ie  number of elements  of the dictionaries lifetime   http   anthon home xs4all nl Python ordereddict

User · Answer

sorted returns a list  hence your error when you try to iterate over it  but because you can t order a dict you will have to deal with a list   I have no idea what the larger context of your code is  but you could try adding an iterator to the resulting list   like this maybe    return iter sorted dict iteritems       of course you will be getting back tuples now because sorted turned your dict into a list of tuples  ex   say your dict was     a  1  c  3  b  2  sorted turns it into a list      a  1    b  2    c  3     so when you actually iterate over the list you get back  in this example  a tuple composed of a string and an integer  but at least you will be able to iterate over it

User · Answer

gt  gt  gt  import heapq  gt  gt  gt  d     c   2   b   9   a   4   d   8   gt  gt  gt  def iter sorted d           keys   list d          heapq heapify keys    Transforms to heap in O N  time         while keys              k   heapq heappop keys    takes O log n  time             yield  k  d k      gt  gt  gt  i   iter sorted d   gt  gt  gt  for x in i          print x     a   4    b   9    c   2    d   8    This method still has an O N log N  sort  however  after a short linear heapify  it yields the items in sorted order as it goes  making it theoretically more efficient when you do not always need the whole list

User · Answer

sorted returns a list  hence your error when you try to iterate over it  but because you can t order a dict you will have to deal with a list   I have no idea what the larger context of your code is  but you could try adding an iterator to the resulting list   like this maybe    return iter sorted dict iteritems       of course you will be getting back tuples now because sorted turned your dict into a list of tuples  ex   say your dict was     a  1  c  3  b  2  sorted turns it into a list      a  1    b  2    c  3     so when you actually iterate over the list you get back  in this example  a tuple composed of a string and an integer  but at least you will be able to iterate over it

User · Answer

A dict s keys are stored in a hashtable so that is their  natural order   i e  psuedo-random  Any other ordering is a concept of the consumer of the dict   sorted   always returns a list  not a dict  If you pass it a dict items    which produces a list of tuples   it will return a list of tuples   k1 v1    k2 v2        which can be used in a loop in a way very much like a dict  but it is not in anyway a dict   foo          a      1       b      2       c      3         print foo  gt  gt  gt    a   1   c   3   b   2   print foo items    gt  gt  gt     a   1     c   3     b   2    print sorted foo items     gt  gt  gt     a   1     b   2     c   3     The following feels like a dict in a loop  but it s not  it s a list of tuples being unpacked into k v   for k v in sorted foo items         print k  v   Roughly equivalent to   for k in sorted foo keys         print k  foo k

User · Answer

In general  one may sort a dict like so   for k in sorted d       print k  d k    For the specific case in the question  having a  drop in replacement  for d iteritems    add a function like   def sortdict d    opts           opts so any currently supported sorted   options can be passed     for k in sorted d    opts           yield k  d k    and so the ending line changes from  return dict iteritems     to  return sortdict dict    or  return sortdict dict  reverse   True

User · Answer

gt  gt  gt  import heapq  gt  gt  gt  d     c   2   b   9   a   4   d   8   gt  gt  gt  def iter sorted d           keys   list d          heapq heapify keys    Transforms to heap in O N  time         while keys              k   heapq heappop keys    takes O log n  time             yield  k  d k      gt  gt  gt  i   iter sorted d   gt  gt  gt  for x in i          print x     a   4    b   9    c   2    d   8    This method still has an O N log N  sort  however  after a short linear heapify  it yields the items in sorted order as it goes  making it theoretically more efficient when you do not always need the whole list

User · Answer

Use the sorted   function   return sorted dict iteritems      If you want an actual iterator over the sorted results  since sorted   returns a list  use   return iter sorted dict iteritems

User · Answer

Greg s answer is right  Note that in Python 3 0 you ll have to do   sorted dict items      as iteritems will be gone

User · Answer

Use the sorted   function   return sorted dict iteritems      If you want an actual iterator over the sorted results  since sorted   returns a list  use   return iter sorted dict iteritems

User · Answer

A dict s keys are stored in a hashtable so that is their  natural order   i e  psuedo-random  Any other ordering is a concept of the consumer of the dict   sorted   always returns a list  not a dict  If you pass it a dict items    which produces a list of tuples   it will return a list of tuples   k1 v1    k2 v2        which can be used in a loop in a way very much like a dict  but it is not in anyway a dict   foo          a      1       b      2       c      3         print foo  gt  gt  gt    a   1   c   3   b   2   print foo items    gt  gt  gt     a   1     c   3     b   2    print sorted foo items     gt  gt  gt     a   1     b   2     c   3     The following feels like a dict in a loop  but it s not  it s a list of tuples being unpacked into k v   for k v in sorted foo items         print k  v   Roughly equivalent to   for k in sorted foo keys         print k  foo k

User · Answer

sorted returns a list  hence your error when you try to iterate over it  but because you can t order a dict you will have to deal with a list   I have no idea what the larger context of your code is  but you could try adding an iterator to the resulting list   like this maybe    return iter sorted dict iteritems       of course you will be getting back tuples now because sorted turned your dict into a list of tuples  ex   say your dict was     a  1  c  3  b  2  sorted turns it into a list      a  1    b  2    c  3     so when you actually iterate over the list you get back  in this example  a tuple composed of a string and an integer  but at least you will be able to iterate over it

User · Answer

If you want to sort by the order that items were inserted instead of of the order of the keys  you should have a look to Python s collections OrderedDict   Python 3 only

User · Answer

Assuming you are using CPython 2 x and have a large dictionary mydict  then using sorted mydict  is going to be slow because sorted builds a sorted list of the keys of mydict   In that case you might want to look at my ordereddict package which includes a C implementation of sorteddict in C  Especially if you have to go over the sorted list of keys multiple times at different stages  ie  number of elements  of the dictionaries lifetime   http   anthon home xs4all nl Python ordereddict

[python] In Python, how do I iterate over a dictionary in sorted key order?

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