How can I remove a key from a Python dictionary?

Question

When deleting a key from a dictionary, I use:

if 'key' in my_dict:     del my_dict['key'] 

Is there a one line way of doing this?

Answer 1

To delete a key regardless of whether it is in the dictionary, use the two-argument form of dict.pop():

my_dict.pop('key', None) 

This will return my_dict[key] if key exists in the dictionary, and None otherwise. If the second parameter is not specified (i.e. my_dict.pop('key')) and key does not exist, a KeyError is raised.

To delete a key that is guaranteed to exist, you can also use:

del my_dict['key'] 

This will raise a KeyError if the key is not in the dictionary.

Answer 2

Specifically to answer "is there a one line way of doing this?"

if 'key' in my_dict: del my_dict['key'] 

...well, you asked ;-)

You should consider, though, that this way of deleting an object from a dict is not atomic—it is possible that 'key' may be in my_dict during the if statement, but may be deleted before del is executed, in which case del will fail with a KeyError. Given this, it would be safest to either use dict.pop or something along the lines of

try:     del my_dict['key'] except KeyError:     pass 

which, of course, is definitely not a one-liner.