Delete an element from a dictionary

python dictionary del
richzilla picture richzilla · Apr 30, 2011 · Viewed 1.8M times · Source

Is there a way to delete an item from a dictionary in Python?

Additionally, how can I delete an item from a dictionary to return a copy (i.e., not modifying the original)?

Answer

Greg Hewgill picture Greg Hewgill · Apr 30, 2011

The del statement removes an element:

del d[key]

However, 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).

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