How to get the difference between two dictionaries in Python

Question

I have two dictionaries  I need to find the difference between the two which should give me both key and value   I have searched and found some addons packages like datadiff  dictdiff-master but when I try it in Python 2 7 it says no such module defined   I used set here    first dict      second dict       value   set second dict -set first dict  print value   output    set   SCD-3547    SCD-3456     I am getting only key  I need to even get the values

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Another solution would be dictdiffer  https   github com inveniosoftware dictdiffer    import dictdiffer                                            a dict                                                         a    foo      b    bar      d    barfoo                                                               b dict                                                         a    foo                                                    b    BAR      c    foobar                                                               for diff in list dictdiffer diff a dict  b dict                 print diff   A diff is a tuple with the type of change  the changed value  and the path to the entry     change    b     bar    BAR      add          c    foobar       remove          d    barfoo

User · Answer

Try the following snippet  using a dictionary comprehension   value     k   second dict k  for k in set second dict  - set first dict      In the above code we find the difference of the keys and then rebuild a dict taking the corresponding values

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What about this  Not as pretty but explicit   orig dict     a    1   b    2  new dict     a    2   v     hello    b    2   updates      for k2  v2 in new dict items        if k2 in orig dict              if v2    orig dict k2               updates update  k2   v2       else          updates update  k2   v2     test it  value of  a  was changed   v  is a completely new entry assert all k in updates for k in   a    v

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I think it s better to use the symmetric difference operation of sets to do that Here is the link to the doc    gt  gt  gt  dict1    1  donkey   2  chicken   3  dog    gt  gt  gt  dict2    1  donkey   2  chimpansee   4  chicken    gt  gt  gt  set1   set dict1 items     gt  gt  gt  set2   set dict2 items     gt  gt  gt  set1   set2   2   chimpansee     4   chicken     2   chicken     3   dog      It is symmetric because    gt  gt  gt  set2   set1   2   chimpansee     4   chicken     2   chicken     3   dog      This is not the case when using the difference operator    gt  gt  gt  set1 - set2   2   chicken     3   dog     gt  gt  gt  set2 - set1   2   chimpansee     4   chicken      However it may not be a good idea to convert the resulting set to a dictionary because you may lose information    gt  gt  gt  dict set1   set2   2   chicken   3   dog   4   chicken

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You were right to look at using a set  we just need to dig in a little deeper to get your method to work   First  the example code   test 1     foo    bar    FOO    BAR   test 2     foo    bar    f00    b r     We can see right now that both dictionaries contain a similar key value pair     foo    bar          Each dictionary also contains a completely different key value pair  But how do we detect the difference  Dictionaries don t support that  Instead  you ll want to use a set   Here is how to turn each dictionary into a set we can use   set 1   set test 1 items    set 2   set test 2 items      This returns a set containing a series of tuples  Each tuple represents one key value pair from your dictionary   Now  to find the difference between set 1 and set 2   print set 1 - set 2  gt  gt  gt     FOO    BAR      Want a dictionary back  Easy  just   dict set 1 - set 2   gt  gt  gt    FOO    BAR

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This function gives you all the diffs  and what stayed the same  based on the dictionary keys only  It also highlights some nice Dict comprehension  Set operations and python 3 6 type annotations    from typing import Dict  Any  Tuple def get dict diffs a  Dict str  Any   b  Dict str  Any   - gt  Tuple Dict str  Any   Dict str  Any   Dict str  Any   Dict str  Any         added to b dict  Dict str  Any     k  b k  for k in set b  - set a       removed from a dict  Dict str  Any     k  a k  for k in set a  - set b       common dict a  Dict str  Any     k  a k  for k in set a   amp  set b       common dict b  Dict str  Any     k  b k  for k in set a   amp  set b       return added to b dict  removed from a dict  common dict a  common dict b  If you want to compare the dictionary values  values in b not a dict    k   b k  for k    in set b items    - set a items

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def flatten it d       if isinstance d  list  or isinstance d  tuple           return tuple  flatten it item  for item in d       elif isinstance d  dict           return tuple   flatten it k   flatten it v   for k  v in sorted d items          else          return d  dict1     a   1   b   2   c   3  dict2     a   1   b   1   print set flatten it dict1   - set flatten it dict2     set    b   2     c   3      or  print set flatten it dict2   - set flatten it dict1     set    b   1

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Old question  but thought I d share my solution anyway  Pretty simple   dicta set   set dicta items      creates a set of tuples  k v pairs  dictb set   set dictb items    setdiff   dictb set difference dicta set    any set method you want for comparisons for k  v in setdiff    unpack the tuples for processing     print f k v differences    k    v      This code creates two sets of tuples representing the k v pairs  It then uses a set method of your choosing to compare the tuples  Lastly  it unpacks the tuples  k v pairs  for processing

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A function using the symmetric difference set operator  as mentioned in other answers  which preserves the origins of the values   def diff dicts a  b  missing KeyError               Find keys and values which differ from  a  to  b  as a dict       If a value differs from  a  to  b  then the value in the returned dict will     be    a value  b value    If either is missing then the token from       missing  will be used instead        param a  The from dict      param b  The to dict      param missing  A token used to indicate the dict did not include this key      return  A dict of keys to tuples with the matching value from a and b             return           key   a get key  missing   b get key  missing           for key in dict              set a items      set b items              keys           Example  print diff dicts   a   1   b   1     b   2   c   2         c     lt class  KeyError  gt   2    a    1   lt class  KeyError  gt     b    1  2     How this works  We use the symmetric difference set operator on the tuples generated from taking items  This generates a set of distinct  key  value  tuples from the two dicts   We then make a new dict from that to collapse the keys together and iterate over these  These are the only keys that have changed from one dict to the next   We then compose a new dict using these keys with a tuple of the values from each dict substituting in our missing token when the key isn t present

[python] How to get the difference between two dictionaries in Python?

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