How can I add new keys to a dictionary?

Question

Is it possible to add a key to a Python dictionary after it has been created?

It doesn\'t seem to have an .add() method.

Answer 1

This popular question addresses functional methods of merging dictionaries a and b.

Here are some of the more straightforward methods (tested in Python 3)...

c = dict( a, **b ) ## see also https://stackoverflow.com/q/2255878
c = dict( list(a.items()) + list(b.items()) )
c = dict( i for d in [a,b] for i in d.items() )

Note: The first method above only works if the keys in b are strings.

To add or modify a single element, the b dictionary would contain only that one element...

c = dict( a, **{'d':'dog'} ) ## returns a dictionary based on 'a'

This is equivalent to...

def functional_dict_add( dictionary, key, value ):
   temp = dictionary.copy()
   temp[key] = value
   return temp

c = functional_dict_add( a, 'd', 'dog' )