Append a dictionary to a dictionary [duplicate]

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...

Answer 1

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,

>>> d1 = {1: 1, 2: 2} >>> d2 = {2: 'ha!', 3: 3} >>> d1.update(d2) >>> d1 {1: 1, 2: 'ha!', 3: 3} 

Answer 2

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.