Python update a key in dict if it doesn't exist
You do not need to call d.keys()
, so
if key not in d:
d[key] = value
is enough. There is no clearer, more readable method.
You could update again with dict.get()
, which would return an existing value if the key is already present:
d[key] = d.get(key, value)
but I strongly recommend against this; this is code golfing, hindering maintenance and readability.
Use dict.setdefault()
:
>>> d = {1: 'one'}
>>> d.setdefault(1, '1')
'one'
>>> d # d has not changed because the key already existed
{1: 'one'}
>>> d.setdefault(2, 'two')
'two'
>>> d
{1: 'one', 2: 'two'}
Since Python 3.9 you can use the merge operator |
to merge two dictionaries. The dict on the right takes precedence:
new_dict = old_dict | { key: val }
For example:
new_dict = { 'a': 1, 'b': 2 } | { 'b': 42 }
print(new_dict} # {'a': 1, 'b': 42}
Note: this creates a new dictionary with the updated values.