Delete an element from a dictionary

Question

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 1

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.

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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).

Answer 2

pop mutates the dictionary.

 >>> lol = {"hello": "gdbye"}  >>> lol.pop("hello")      'gdbye'  >>> lol      {} 

If you want to keep the original you could just copy it.