Calculate difference in keys contained in two Python dictionaries

Question

Suppose I have two Python dictionaries - dictA and dictB  I need to find out if there are any keys which are present in dictB but not in dictA  What is the fastest way to go about it   Should I convert the dictionary keys into a set and then go about   Interested in knowing your thoughts        Thanks for your responses   Apologies for not stating my question properly  My scenario is like this - I have a dictA which can be the same as dictB or may have some keys missing as compared to dictB or else the value of some keys might be different which has to be set to that of dictA key s value   Problem is the dictionary has no standard and can have values which can be dict of dict   Say  dictA   key1  a   key2  b   key3    key11  cc   key12  dd    key4    key111           dictB   key1  a   key2   newb   key3    key11  cc   key12  newdd   key13  ee           So  key2  value has to be reset to the new value and  key13  has to be added inside the dict  The key value does not have a fixed format  It can be a simple value or a dict or a dict of dict

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As mentioned in other answers  unittest produces some nice output for comparing dicts  but in this example we don t want to have to build a whole test first   Scraping the unittest source  it looks like you can get a fair solution with just this   import difflib import pprint  def diff dicts a  b       if a    b          return        return   n  join          difflib ndiff pprint pformat a  width 30  splitlines                          pprint pformat b  width 30  splitlines            so  dictA   dict zip range 7   map ord   python     dictB    0  112  1   spam   2   1 2 3   3  104  4  111  print diff dicts dictA  dictB    Results in    0  112  -  1  121  -  2  116     1   spam      2   1  2  3      3  104  -  4  111                 4  111              -  5  110    Where     -  indicates key values in the first but not second dict     indicates key values in the second but not the first dict   Like in unittest  the only caveat is that the final mapping can be thought to be a diff  due to the trailing comma bracket

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There is an other question in stackoverflow about this argument and i have to admit that there is a simple solution explained  the datadiff library of python helps printing the difference between two dictionaries

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If on Python   2 7     update different values in dictB   I would assume only dictA should be updated    but the question specifies otherwise  for k in dictA viewkeys    amp  dictB viewkeys        if dictA k     dictB k           dictB k   dictA k     add missing keys to dictA  dictA update   k dictB k   for k in dictB viewkeys   - dictA viewkeys

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Not sure if it is still relevant but I came across this problem  my situation i just needed to return a dictionary of the changes for all nested dictionaries etc etc  Could not find a good solution out there but I did end up writing a simple function to do this  Hope this helps

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Here s a way that will work  allows for keys that evaluate to False  and still uses a generator expression to fall out early if possible  It s not exceptionally pretty though   any map lambda x  True   k for k in b if k not in a      EDIT   THC4k posted a reply to my comment on another answer   Here s a better  prettier way to do the above   any True for k in b if k not in a    Not sure how that never crossed my mind

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what about standart  compare FULL Object   PyDev- new PyDev Module- Module  unittest  import unittest   class Test unittest TestCase         def testName self           obj1    1 1  2 2          obj2    1 1  2 2          self maxDiff   None   sometimes is usefull         self assertDictEqual d1  d2   if   name         main          import sys sys argv         Test testName        unittest main

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As Alex Martelli wrote  if you simply want to check if any key in B is not in A  any True  for k in dictB if k not in dictA  would be the way to go   To find the keys that are missing   diff   set dictB -set dictA   sets  C  Dokumente und Einstellungen thc gt python -m timeit -s  dictA       dict zip range 1000  range  1000     dictB   dict zip range 0 2000 2  range 1000      diff set dictB -set dictA   10000 loops  best of 3  107 usec per loop  diff     k for k in dictB if k not in dictA    lc  C  Dokumente und Einstellungen thc gt python -m timeit -s  dictA    dict zip range 1000  range  1000     dictB   dict zip range 0 2000 2  range 1000      diff   k for k in dictB if k not in dictA    10000 loops  best of 3  95 9 usec per loop   So those two solutions are pretty much the same speed

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not sure whether its  fast  or not  but normally  one can do this  dicta     a  1  b  2  c  3  d  4  dictb     a  1  d  2  for key in dicta keys        if not key in dictb          print key

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My recipe of symmetric difference between two dictionaries   def find dict diffs dict1  dict2       unequal keys          unequal keys extend set dict1 keys    symmetric difference set dict2 keys          for k in dict1 keys            if dict1 get k   N A      dict2 get k   N A                unequal keys append k      if unequal keys          print  param    dict1 t    dict2          for k in set unequal keys               print str k    t  dict1 get k   N A     t   dict2 get k   N A       else          print  Dicts are equal   dict1    1  a   2  b   3  c   4  d   5  e   dict2    1  b   2  a   3  c   4  d   6  f    find dict diffs dict1  dict2    And result is   param   dict1   dict2 1       a       b 2       b       a 5       e       N A 6       N A     f

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This is an old question and asks a little bit less than what I needed so this answer actually solves more than this question asks  The answers in this question helped me solve the following     asked  Record differences between two dictionaries Merge differences from  1 into base dictionary  asked  Merge differences between two dictionaries  treat dictionary  2 as if it were a diff dictionary  Try to detect item movements as well as changes  asked  Do all of this recursively   All this combined with JSON makes for a pretty powerful configuration storage support   The solution  also on github    from collections import OrderedDict from pprint import pprint   class izipDestinationMatching object         slots       attr    value    index        def   init   self  attr  value  index           self attr  self value  self index   attr  value  index      def   repr   self           return  izip destination matching  found match by   s      s     d     self attr  self value  self index    def izip destination a  b  attrs  addMarker True               Returns zipped lists  but final size is equal to b with  if shorter  a padded with nulls     Additionally also tries to find item reallocations by searching child dicts  if they are dicts  for attribute  listed in attrs      When addMarker    False  patching   final size will be the longer of a  b             for idx  item in enumerate b           try              attr   next  x for x in attrs if x in item   None     See if the item has any of the ID attributes             match  matchIdx   next   orgItm  idx  for idx  orgItm in enumerate a  if attr in orgItm and orgItm attr     item attr     None  None   if attr else  None  None              if match and matchIdx    idx and addMarker  item izipDestinationMatching    izipDestinationMatching attr  item attr   matchIdx          except              match   None         yield  match if match else a idx  if len a   gt  idx else None   item     if not addMarker and len a   gt  len b           for item in a len b  - len a                 yield item  item   def dictdiff a  b  searchAttrs                  returns a dictionary which represents difference from a to b     the return dict is as short as possible        equal items are removed       added   changed items are listed       removed items are listed with value None     Also processes list values where the resulting list size will match that of b      It can also search said list items  that are dicts  for identity values to detect changed positions        In case such identity value is found  it is kept so that it can be re-found during the merge phase      param a  original dict      param b  new dict      param searchAttrs  list of strings  keys to search for in sub-dicts       return  dict   list   whatever input is             if not  isinstance a  dict  and isinstance b  dict            if isinstance a  list  and isinstance b  list               return  dictdiff v1  v2  searchAttrs  for v1  v2 in izip destination a  b  searchAttrs           return b     res   OrderedDict       if izipDestinationMatching in b          keepKey   b izipDestinationMatching  attr         del b izipDestinationMatching      else          keepKey   izipDestinationMatching     for key in sorted set a keys     b keys              v1   a get key  None          v2   b get key  None          if keepKey    key or v1    v2  res key    dictdiff v1  v2  searchAttrs      if len res   lt   1  res   dict res     This is only here for pretty print  OrderedDict doesn t pprint nicely      return res   def dictmerge a  b  searchAttrs                  Returns a dictionary which merges differences recorded in b to base dictionary a     Also processes list values where the resulting list size will match that of a     It can also search said list items  that are dicts  for identity values to detect changed positions      param a  original dict      param b  diff dict to patch into a      param searchAttrs  list of strings  keys to search for in sub-dicts       return  dict   list   whatever input is             if not  isinstance a  dict  and isinstance b  dict            if isinstance a  list  and isinstance b  list               return  dictmerge v1  v2  searchAttrs  for v1  v2 in izip destination a  b  searchAttrs  False           return b     res   OrderedDict       for key in sorted set a keys     b keys              v1   a get key  None          v2   b get key  None           print  processing   key  v1  v2  key not in b  dictmerge v1  v2          if v2 is not None  res key    dictmerge v1  v2  searchAttrs          elif key not in b  res key    v1     if len res   lt   1  res   dict res     This is only here for pretty print  OrderedDict doesn t pprint nicely      return res

User · Answer

If you want a built-in solution for a full comparison with arbitrary dict structures   Maxx s answer is a good start   import unittest  test   unittest TestCase   test assertEqual dictA  dictB

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here s a solution that can compare more than two dicts   def diff dict dicts  default None       diff dict            add  list    around  d keys    for python 3 compatibility     for k in set sum  d keys   for d in dicts                   we can just use  values    d get k  default       below if            we don t care that d1 k  default and d2 k  missing will           be treated as equal         if any k not in d for d in dicts               diff dict k     d get k  default  for d in dicts          else              values    d k  for d in dicts              if any v    values 0  for v in values                   diff dict k    values     return diff dict   usage example   import matplotlib pyplot as plt diff dict  plt rcParams  plt rcParamsDefault  plt matplotlib rcParamsOrig

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You can use set operations on the keys   diff   set dictb keys    - set dicta keys      Here is a class to find all the possibilities  what was added  what was removed  which key-value pairs are the same  and which key-value pairs are changed   class DictDiffer object               Calculate the difference between two dictionaries as       1  items added      2  items removed      3  keys same in both but changed values      4  keys same in both and unchanged values             def   init   self  current dict  past dict           self current dict  self past dict   current dict  past dict         self set current  self set past   set current dict keys     set past dict keys            self intersect   self set current intersection self set past      def added self           return self set current - self intersect      def removed self           return self set past - self intersect      def changed self           return set o for o in self intersect if self past dict o     self current dict o       def unchanged self           return set o for o in self intersect if self past dict o     self current dict o     Here is some sample output    gt  gt  gt  a     a   1   b   1   c   0   gt  gt  gt  b     a   1   b   2   d   0   gt  gt  gt  d   DictDiffer b  a   gt  gt  gt  print  Added    d added   Added  set   d     gt  gt  gt  print  Removed    d removed   Removed  set   c     gt  gt  gt  print  Changed    d changed   Changed  set   b     gt  gt  gt  print  Unchanged    d unchanged   Unchanged  set   a      Available as a github repo  https   github com hughdbrown dictdiffer

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Use set     set dictA keys    intersection dictB keys

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Try this to find de intersection  the keys that is in both dictionarie  if you want the keys not found on second dictionarie  just use the not in     intersect   filter lambda x  dictB dictB keys    x in dictB  dictA keys

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Maxx has an excellent answer  use the unittest tools provided by Python   import unittest   class Test unittest TestCase       def runTest self           pass      def testDict self  d1  d2  maxDiff None           self maxDiff   maxDiff         self assertDictEqual d1  d2    Then  anywhere in your code you can call   try      Test   testDict dict1  dict2  except Exception  e      print e   The resulting output looks like the output from diff  pretty-printing the dictionaries with   or - prepending each line that is different

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Here is a solution for deep comparing 2 dictionaries keys   def compareDictKeys dict1  dict2     if type dict1     dict or type dict2     dict        return False    keys1  keys2   dict1 keys    dict2 keys     diff   set keys1  - set keys2  or set keys2  - set keys1     if not diff        for key in keys1            if  type dict1 key      dict or type dict2 key      dict  and not compareDictKeys dict1 key   dict2 key                  diff   True               break    return not diff

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In case you want the difference recursively  I have written a package for python  https   github com seperman deepdiff  Installation  Install from PyPi   pip install deepdiff   Example usage  Importing   gt  gt  gt  from deepdiff import DeepDiff  gt  gt  gt  from pprint import pprint  gt  gt  gt  from   future   import print function   In case running on Python 2   Same object returns empty   gt  gt  gt  t1    1 1  2 2  3 3   gt  gt  gt  t2   t1  gt  gt  gt  print DeepDiff t1  t2        Type of an item has changed   gt  gt  gt  t1    1 1  2 2  3 3   gt  gt  gt  t2    1 1  2  2   3 3   gt  gt  gt  pprint DeepDiff t1  t2   indent 2     type changes      root 2       newtype    lt class  str  gt                                     newvalue    2                                     oldtype    lt class  int  gt                                     oldvalue   2      Value of an item has changed   gt  gt  gt  t1    1 1  2 2  3 3   gt  gt  gt  t2    1 1  2 4  3 3   gt  gt  gt  pprint DeepDiff t1  t2   indent 2    values changed     root 2      newvalue   4   oldvalue   2      Item added and or removed   gt  gt  gt  t1    1 1  2 2  3 3  4 4   gt  gt  gt  t2    1 1  2 4  3 3  5 5  6 6   gt  gt  gt  ddiff   DeepDiff t1  t2   gt  gt  gt  pprint  ddiff    dic item added     root 5     root 6       dic item removed     root 4       values changed     root 2      newvalue   4   oldvalue   2      String difference   gt  gt  gt  t1    1 1  2 2  3 3  4   a   hello    b   world     gt  gt  gt  t2    1 1  2 4  3 3  4   a   hello    b   world      gt  gt  gt  ddiff   DeepDiff t1  t2   gt  gt  gt  pprint  ddiff  indent   2     values changed      root 2      newvalue   4   oldvalue   2                          root 4   b        newvalue    world                                             oldvalue    world       String difference 2   gt  gt  gt  t1    1 1  2 2  3 3  4   a   hello    b   world  nGoodbye  n1 n2 nEnd     gt  gt  gt  t2    1 1  2 2  3 3  4   a   hello    b   world n1 n2 nEnd     gt  gt  gt  ddiff   DeepDiff t1  t2   gt  gt  gt  pprint  ddiff  indent   2     values changed      root 4   b        diff    ---  n                                                        n                                                      -1 5  1 4    n                                                   -world  n                                                   -Goodbye  n                                                    world n                                                    1 n                                                    2 n                                                    End                                            newvalue    world n1 n2 nEnd                                            oldvalue    world  n                                                       Goodbye  n                                                       1 n                                                       2 n                                                       End       gt  gt  gt    gt  gt  gt  print  ddiff  values changed    root 4   b      diff    ---          -1 5  1 4    -world  -Goodbye   world  1  2  End   Type change   gt  gt  gt  t1    1 1  2 2  3 3  4   a   hello    b   1  2  3     gt  gt  gt  t2    1 1  2 2  3 3  4   a   hello    b   world n n nEnd     gt  gt  gt  ddiff   DeepDiff t1  t2   gt  gt  gt  pprint  ddiff  indent   2     type changes      root 4   b        newtype    lt class  str  gt                                          newvalue    world n n nEnd                                          oldtype    lt class  list  gt                                          oldvalue    1  2  3       List difference   gt  gt  gt  t1    1 1  2 2  3 3  4   a   hello    b   1  2  3  4     gt  gt  gt  t2    1 1  2 2  3 3  4   a   hello    b   1  2     gt  gt  gt  ddiff   DeepDiff t1  t2   gt  gt  gt  pprint  ddiff  indent   2    iterable item removed     root 4   b   2    3   root 4   b   3    4     List difference 2    gt  gt  gt  t1    1 1  2 2  3 3  4   a   hello    b   1  2  3     gt  gt  gt  t2    1 1  2 2  3 3  4   a   hello    b   1  3  2  3     gt  gt  gt  ddiff   DeepDiff t1  t2   gt  gt  gt  pprint  ddiff  indent   2     iterable item added     root 4   b   3    3      values changed      root 4   b   1      newvalue   3   oldvalue   2                          root 4   b   2      newvalue   2   oldvalue   3      List difference ignoring order or duplicates   with the same dictionaries as above    gt  gt  gt  t1    1 1  2 2  3 3  4   a   hello    b   1  2  3     gt  gt  gt  t2    1 1  2 2  3 3  4   a   hello    b   1  3  2  3     gt  gt  gt  ddiff   DeepDiff t1  t2  ignore order True   gt  gt  gt  print  ddiff       List that contains dictionary    gt  gt  gt  t1    1 1  2 2  3 3  4   a   hello    b   1  2   1 1  2 2      gt  gt  gt  t2    1 1  2 2  3 3  4   a   hello    b   1  2   1 3      gt  gt  gt  ddiff   DeepDiff t1  t2   gt  gt  gt  pprint  ddiff  indent   2     dic item removed     root 4   b   2  2        values changed     root 4   b   2  1      newvalue   3   oldvalue   1      Sets    gt  gt  gt  t1    1  2  8   gt  gt  gt  t2    1  2  3  5   gt  gt  gt  ddiff   DeepDiff t1  t2   gt  gt  gt  pprint  DeepDiff t1  t2     set item added     root 3     root 5      set item removed     root 8       Named Tuples    gt  gt  gt  from collections import namedtuple  gt  gt  gt  Point   namedtuple  Point     x    y     gt  gt  gt  t1   Point x 11  y 22   gt  gt  gt  t2   Point x 11  y 23   gt  gt  gt  pprint  DeepDiff t1  t2     values changed     root y     newvalue   23   oldvalue   22      Custom objects    gt  gt  gt  class ClassA object           a   1         def   init   self  b               self b   b       gt  gt  gt  t1   ClassA 1   gt  gt  gt  t2   ClassA 2   gt  gt  gt    gt  gt  gt  pprint DeepDiff t1  t2     values changed     root b     newvalue   2   oldvalue   1      Object attribute added    gt  gt  gt  t2 c    new attribute   gt  gt  gt  pprint DeepDiff t1  t2     attribute added     root c      values changed     root b     newvalue   2   oldvalue   1

User · Answer

Based on ghostdog74 s answer   dicta     a  1  d  2  dictb     a  5  d  2   for value in dicta values        if not value in dictb values            print value   will print differ value of dicta

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The top answer by hughdbrown suggests using set difference  which is definitely the best approach   diff   set dictb keys    - set dicta keys      The problem with this code is that it builds two lists just to create two sets  so it s wasting 4N time and 2N space  It s also a bit more complicated than it needs to be   Usually  this is not a big deal  but if it is   diff   dictb keys   - dicta    You don t need to convert the right dict to a set  set difference takes any iterable  and a dict is an iterable of its keys   You also don t need to convert the left dict to a set  because anything that complies with collections abc Mapping has a KeysView that acts like a Set    Python 2  In Python 2  keys   returns a list of the keys  not a KeysView  So you have to ask for viewkeys   directly   diff   dictb viewkeys   - dicta   For dual-version 2 7 3 x code  you re hopefully using six or something similar  so you can use six viewkeys dictb    diff   six viewkeys dictb  - dicta   In 2 4-2 6  there is no KeysView  But you can at least cut the cost from 4N to N by building your left set directly out of an iterator  instead of building a list first   diff   set dictb  - dicta   Items     I have a dictA which can be the same as dictB or may have some keys missing as compared to dictB or else the value of some keys might be different   So you really don t need to compare the keys  but the items  An ItemsView is only a Set if the values are hashable  like strings  If they are  it s easy   diff   dictb items   - dicta items     Recursive diff  Although the question isn t directly asking for a recursive diff  some of the example values are dicts  and it appears the expected output does recursively diff them  There are already multiple answers here showing how to do that

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If you really mean exactly what you say  that you only need to find out IF  there are any keys  in B and not in A  not WHICH ONES might those be if any   the fastest way should be   if any True for k in dictB if k not in dictA         If you actually need to find out WHICH KEYS  if any  are in B and not in A  and not just  IF  there are such keys  then existing answers are quite appropriate  but I do suggest more precision in future questions if that s indeed what you mean -

[python] Calculate difference in keys contained in two Python dictionaries

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