Delete an element from a dictionary

• How do I delete an item from a dictionary in Python?

• Without modifying the original dictionary, how do I obtain another dictionary with the item removed?

See also How can I remove a key from a Python dictionary? for the specific issue of removing an item (by key) that may not already be present.

The del statement removes an element:

del d[key]

Note that this mutates the existing dictionary, so the contents of the dictionary changes for anybody else who has a reference to the same instance. To return a new dictionary, make a copy of the dictionary:

def removekey(d, key):
    r = dict(d)
    del r[key]
    return r

The dict() constructor makes a shallow copy. To make a deep copy, see the copy module.

Note that making a copy for every dict del/assignment/etc. means you're going from constant time to linear time, and also using linear space. For small dicts, this is not a problem. But if you're planning to make lots of copies of large dicts, you probably want a different data structure, like a HAMT (as described in this answer).

Stack Overflow Q#5844672, score: 2572