Delete a dictionary item if the key exists

Question

Is there any other way to delete an item in a dictionary only if the given key exists  other than   if key in mydict      del mydict key    The scenario is that I m given a collection of keys to be removed from a given dictionary  but I am not certain if all of them exist in the dictionary  Just in case I miss a more efficient solution

User · Accepted Answer

You can use  dict pop    mydict pop  key   None    Note that if the second argument  i e  None is not given  KeyError is raised if the key is not in the dictionary  Providing the second argument prevents the conditional exception

User · Answer

Approach  calculate keys to remove  mutate dict  Let s call keys the list iterator of keys that you are given to remove  I d do this   keys to remove   set keys  intersection set mydict keys     for key in keys to remove      del mydict key    You calculate up front all the affected items and operate on them   Approach  calculate keys to keep  make new dict with those keys  I prefer to create a new dictionary over mutating an existing one  so I would probably also consider this   keys to keep   set mydict keys    - set keys  new dict    k  v for k  v in mydict iteritems   if k in keys to keep    or   keys to keep   set mydict keys    - set keys  new dict    k  mydict k  for k in keys to keep

User · Answer

There is also   try      del mydict key  except KeyError      pass   This only does 1 lookup instead of 2   However  except clauses are expensive  so if you end up hitting the except clause frequently  this will probably be less efficient than what you already have

[python] Delete a dictionary item if the key exists

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