Append a dictionary to a dictionary

Question

I have two existing dictionaries  and I wish to  append  one of them to the other  By that I mean that the key values of the other dictionary should be made into the first dictionary  For example   orig         A   1      B   2      C   3     extra         D   4      E   5     dest     Something here involving orig and extra  print dest       A   1      B   2      C   3      D   4      E   5     I think this all can be achieved through a for loop  maybe    but is there some method of dictionaries or any other module that saves this job for me  The actual dictionaries I m using are really big

User · Answer

dict update   looks like it will do what you want      gt  gt  orig update extra   gt  gt  gt  orig   A   1   C   3   B   2   E   5   D   4   gt  gt  gt     Perhaps  though  you don t want to update your original dictionary  but work on a copy    gt  gt  gt  dest   orig copy    gt  gt  gt  dest update extra   gt  gt  gt  orig   A   1   C   3   B   2   gt  gt  gt  dest   A   1   C   3   B   2   E   5   D   4

User · Answer

You can do  orig update extra    or  if you don t want orig to be modified  make a copy first   dest   dict orig     or orig copy   dest update extra    Note that if extra and orig have overlapping keys  the final value will be taken from extra  For example    gt  gt  gt  d1    1  1  2  2   gt  gt  gt  d2    2   ha    3  3   gt  gt  gt  d1 update d2   gt  gt  gt  d1  1  1  2   ha    3  3

User · Answer

There are two ways to add one dictionary to another  Update  modifies orig in place  orig update extra       Python 2 7  orig    extra           Python 3 9   Merge  creates a new dictionary    Python 2 7  dest   collections ChainMap orig  extra  dest    k  v for d in  orig  extra  for  k  v  in d items       Python 3 dest      orig    extra            dest      orig   D   4   E   5     Python 3 9   dest   orig   extra   Note that these operations are noncommutative  In all cases  the latter is the winner  E g  orig      A   1   B   2  extra     A   3   C   3   dest   orig   extra   dest     A   3   B   2   C   3   dest   extra   orig   dest     A   1   B   2   C   3   It is also important to note that only from Python 3 7  and CPython 3 6  dicts are ordered  So  in previous versions  the order of the items in the dictionary may vary

User · Answer

Assuming that you do not want to change orig  you can either do a copy and update like the other answers  or you can create a new dictionary in one step by passing all items from both  dictionaries into the dict constructor   from itertools import chain dest   dict chain orig items    extra items       Or without itertools   dest   dict list orig items      list extra items       Note that you only need to pass the result of items   into list   on Python 3  on 2 x dict items   already returns a list so you can just do dict orig items     extra items      As a more general use case  say you have a larger list of dicts that you want to combine into a single dict  you could do something like this   from itertools import chain dest   dict chain from iterable map dict items  list of dicts

User · Answer

There is the  update   method        update  other     Update the dictionary with the key value pairs from other  overwriting existing keys  Return None       update   accepts either another dictionary object or an iterable of key value pairs  as tuples or other iterables of length two   If   keyword arguments are specified  the dictionary is then updated with   those key value pairs  d update red 1  blue 2        Changed in version 2 4  Allowed the argument to be an iterable of key value pairs and allowed keyword arguments

User · Answer

A three-liner to combine or merge two dictionaries   dest      dest update orig  dest update extra    This creates a new dictionary dest without modifying orig and extra   Note  If a key has different values in orig and extra  then extra overrides orig

User · Answer

The answer I want to give is  use collections ChainMap   but I just discovered that it was only added in Python 3 3  https   docs python org 3 3 library collections html chainmap-objects  You can try to crib the class from the 3 3 source though  http   hg python org cpython file 3 3 Lib collections init py l763  Here is a less feature-full Python 2 x compatible version  same author   http   code activestate com recipes 305268-chained-map-lookups   Instead of expanding overwriting one dictionary with another using dict merge  or creating an additional copy merging both  you create a lookup chain that searches both in order  Because it doesn t duplicate the mappings it wraps ChainMap uses very little memory  and sees later modifications to any sub-mapping  Because order matters you can also use the chain to layer defaults  i e  user prefs   config   env

[python] Append a dictionary to a dictionary

Examples related to python

Examples related to dictionary