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

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I prefer the immutable version  foo         1 1      2 2      3 3   removeKeys    1 2  def woKeys dct  keyIter       return           k v         for k v in dct items   if k not in keyIter         gt  gt  gt  print woKeys foo  removeKeys    3  3   gt  gt  gt  print foo   1  1  2  2  3  3

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del my dict key  is slightly faster than my dict pop key  for removing a key from a dictionary when the key exists   gt  gt  gt  import timeit  gt  gt  gt  setup    d    i  i for i in range 100000      gt  gt  gt  timeit timeit  del d 3    setup setup  number 1  1 79e-06  gt  gt  gt  timeit timeit  d pop 3    setup setup  number 1  2 09e-06  gt  gt  gt  timeit timeit  d2    key  val for key  val in d items   if key    3    setup setup  number 1  0 00786   But when the key doesn t exist if key in my dict  del my dict key  is slightly faster than my dict pop key  None   Both are at least three times faster than del in a try except statement    gt  gt  gt  timeit timeit  if  missing key  in d  del d  missing key     setup setup  0 0229  gt  gt  gt  timeit timeit  d pop  missing key   None    setup setup  0 0426  gt  gt  gt  try except           try          del d  missing key       except KeyError          pass          gt  gt  gt  timeit timeit try except  setup setup  0 133

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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

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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  ie  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

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Using the  del  keyword   del dict key

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It took me some time to figure out what exactly my dict pop  quot key quot   None  is doing  So I ll add this as an answer to save others googling time   pop key   default   If key is in the dictionary  remove it and return its value  else return default  If default is not given and key is not in the dictionary  a KeyError is raised   Documentation

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You can use exception handling if you want to be very verbose   try       del dict key   except KeyError  pass   This is slower  however  than the pop   method  if the key doesn t exist   my dict pop  key   None    It won t matter for a few keys  but if you re doing this repeatedly  then the latter method is a better bet   The fastest approach is this   if  key  in dict       del myDict  key     But this method is dangerous because if  key  is removed in between the two lines  a KeyError will be raised

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We can delete a key from a Python dictionary by the some of the following approaches  Using the del keyword  it s almost the same approach like you did though -  myDict     one   100   two   200   three   300    print myDict       one   100   two   200   three   300   if myDict get  one     del myDict  one    print myDict       two   200   three   300   Or We can do like the following  But one should keep in mind that  in this process actually it won t delete any key from the dictionary rather than making a specific key excluded from that dictionary  In addition  I observed that it returned a dictionary which was not ordered the same as myDict  myDict     one   100   two   200   three   300   four   400   five   500   key value for key  value in myDict items   if key     one    If we run it in the shell  it ll execute something like   five   500   four   400   three   300   two   200  - notice that it s not the same ordered as myDict  Again if we try to print myDict  then we can see all keys including which we excluded from the dictionary by this approach  However  we can make a new dictionary by assigning the following statement into a variable  var    key value for key  value in myDict items   if key     one    Now if we try to print it  then it ll follow the parent order  print var      two   200   three   300   four   400   five   500   Or Using the pop   method  myDict     one   100   two   200   three   300  print myDict   if myDict get  one     myDict pop  one   print myDict       two   200   three   300   The difference between del and pop is that  using pop   method  we can actually store the key s value if needed  like the following  myDict     one   100   two   200   three   300  if myDict get  one     var   myDict pop  one   print myDict      two   200   three   300  print var       100  Fork this gist for future reference  if you find this useful

User · Answer

Dictionary data type has  a method called dict name pop item  and this can be used to delete a key value pair from a dictionary  a  9 4 2 3 4 2 1 3  a pop 9  print a   This will give the output as   2  3  4  2  1  3   This way you can delete an item from a dictionary in one line

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Another way is by using items     dict comprehension  items   coupled with dict comprehension can also help us achieve the task of key-value pair deletion  but it has the drawback of not being an in place dict technique  Actually a new dict if created except for the key we don   t wish to include  test dict     quot sai quot    22   quot kiran quot    21   quot vinod quot    21   quot sangam quot    21     Printing dictionary before removal print   quot dictionary before performing remove is    quot    str test dict      Using items     dict comprehension to remove a dict  pair   removes  vinod new dict    key val for key  val in test dict items   if key     vinod      Printing dictionary after removal print   quot dictionary after remove is    quot    str new dict    Output  dictionary before performing remove is     sai   22   kiran   21   vinod   21   sangam   21  dictionary after remove is     sai   22   kiran   21   sangam   21

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Single filter on key   return  key  and remove it from my dict if  key  exists in my dict return None if  key  doesn t exist in my dict      this will change my dict in place  mutable    my dict pop  key   None    Multiple filters on keys     generate a new dict  immutable    dic1          x  1       y   2       z   3    def func1 item       return  item 0     x  and item 0      y   print      dict          filter              lambda item  item 0      x  and item 0      y                dic1 items

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You can use a dictionary comprehension to create a new dictionary with that key removed    gt  gt  gt  my dict    k  v for k  v in my dict items   if k     key     You can delete by conditions  No error if key doesn t exist

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If you need to remove a lot of keys from a dictionary in one line of code  I think using map   is quite succinct and Pythonic readable   myDict     a  1  b  2  c  3  d  4  map myDict pop    a   c      The list of keys to remove  gt  gt  gt  myDict   b   2   d   4    And if you need to catch errors where you pop a value that isn t in the dictionary  use lambda inside map   like this   map lambda x  myDict pop x None     a    c    e     1  3  None    pop returns  gt  gt  gt  myDict   b   2   d   4    or in python3  you must use a list comprehension instead    myDict pop x  None  for x in   a    c    e      It works  And  e  did not cause an error  even though myDict did not have an  e  key

[python] How can I remove a key from a Python dictionary?

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