Removing multiple keys from a dictionary safely

Question

I know how to remove an entry   key  from my dictionary d  safely  You do  if d has key  key        del d  key    However  I need to remove multiple entries from a dictionary safely   I was thinking of defining the entries in a tuple as I will need to do this more than once  entities to remove     a    b    c   for x in entities to remove      if x in d          del d x   However  I was wondering if there is a smarter way to do this

User · Accepted Answer

Why not like this   entries     a    b    c   the dict     b    foo    def entries to remove entries  the dict       for key in entries          if key in the dict              del the dict key    A more compact version was provided by mattbornski using dict pop

User · Answer

Using Dict Comprehensions  final dict    key  t key  for key in t if key not in  key1  key2     where key1 and key2 are to be removed   In the example below  keys  b  and  c  are to be removed  amp  it s kept in a keys list    gt  gt  gt  a   a   1   c   3   b   2   d   4   gt  gt  gt  keys     b    c    gt  gt  gt  print  key  a key  for key in a if key not in keys    a   1   d   4   gt  gt  gt

User · Answer

I m late to this discussion but for anyone else  A solution may be to create a list of keys as such   k     a   b   c   d     Then use pop   in a list comprehension  or for loop  to iterate over the keys and pop one at a time as such   new dictionary    dictionary pop x   n a   for x in k    The  n a  is in case the key does not exist  a default value needs to be returned

User · Answer

I have tested the performance of three methods    Method 1   del  for key in remove keys      if key in d          del d key     Method 2   pop    for key in remove keys      d pop key  None     Method 3  comprehension  key  v for key  v in d items   if key not in remove keys   Here are the results of 1M iterations   del  2 03s 2 0 ns iter  100   pop    2 38s 2 4 ns iter  117   comprehension  4 11s 4 1 ns iter  202    So both del and pop   are the fastest  Comprehensions are 2x slower  But anyway  we speak nanoseconds here    Dicts in Python are ridiculously fast

User · Answer

I think using the fact that the keys can be treated as a set is the nicest way if you re on python 3   def remove keys d  keys       to remove   set keys      filtered keys   d keys   - to remove     filtered values   map d get  filtered keys      return dict zip filtered keys  filtered values     Example    gt  gt  gt  remove keys   k1   1   k3   3     k1    k2      k3   3

User · Answer

Some timing tests for cpython 3 shows that a simple for loop is the fastest way  and it s quite readable    Adding in a function doesn t cause much overhead either   timeit results  10k iterations     all x pop v  for v in r       0 85 all map x pop  r              0 60 list map x pop  r             0 70 all map x   delitem    r      0 44 del all x  r                  0 40  lt inline for loop gt  x  r        0 35   def del all mapping  to remove            Remove list of elements from mapping           for key in to remove            del mapping key    For small iterations  doing that  inline  was a bit faster  because of the overhead of the function call    But del all is lint-safe  reusable  and faster than all the python comprehension and mapping constructs

User · Answer

If you also need to retrieve the values for the keys you are removing  this would be a pretty good way to do it  values removed    d pop k  None  for k in entities to remove   You could of course still do this just for the removal of the keys from d  but you would be unnecessarily creating the list of values with the list comprehension   It is also a little unclear to use a list comprehension just for the function s side effect

User · Answer

Why not   entriestoremove    2 5 1  for e in entriestoremove      if d has key e           del d e    I don t know what you mean by  smarter way   Surely there are other ways  maybe with dictionary comprehensions   entriestoremove    2 5 1  newdict    x for x in d if x not in entriestoremove

User · Answer

a solution is using map and filter functions  python 2  d   a  1  b  2  c  3  l   a   b   d   map d   delitem    filter d   contains   l   print d    python 3  d   a  1  b  2  c  3  l   a   b   d   list map d   delitem    filter d   contains   l    print d    you get     c   3

User · Answer

It would be nice to have full support for set methods for dictionaries  and not the unholy mess we re getting with Python 3 9  so that you could simply  remove  a set of keys  However  as long as that s not the case  and you have a large dictionary with potentially a large number of keys to remove  you might want to know about the performance  So  I ve created some code that creates something large enough for meaningful comparisons  a 100 000 x 1000 matrix  so 10 000 00 items in total   from itertools import product from time import perf counter    make a complete worksheet 100000   1000 start   perf counter   prod   product range 1  100000   range 1  1000   cells     x y  x for x y in prod  print len cells    print f Create time  perf counter  -start  2f s   clock   perf counter     remove everything above row 50 000  keys   product range 50000  100000   range 1  100      for x y in keys        del cells x  y   for n in map cells pop  keys       pass  print len cells   stop   perf counter   print f Removal time  stop-clock  2f s     10 million items or more is not unusual in some settings  Comparing the two methods on my local machine I see a slight improvement when using map and pop  presumably because of fewer function calls  but both take around 2 5s on my machine  But this pales in comparison to the time required to create the dictionary in the first place  55s   or including checks within the loop  If this is likely then its best to create a set that is a intersection of the dictionary keys and your filter   keys   cells keys    amp  keys  In summary  del is already heavily optimised  so don t worry about using it

User · Answer

I have no problem with any of the existing answers  but I was surprised to not find this solution   keys to remove     a    b    c   my dict    k  v for k  v in zip  a b c d e f g  split        0  1  2  3  4  5  6     for k in keys to remove      try          del my dict k      except KeyError          pass  assert my dict      d   3   e   4   f   5   g   6    Note  I stumbled across this question coming from here  And my answer is related to this answer

User · Answer

Using dict pop  d     some    data   entries to remove     any    iterable   for k in entries to remove      d pop k  None

User · Answer

Found a solution with pop and map  d     a    valueA    b    valueB    c    valueC    d    valueD   keys     a    b    c   list map d pop  keys   print d    The output of this     d    valueD     I have answered this question so late just because I think it will help in the future if anyone searches the same  And this might help   Update  The above code will throw an error if a key does not exist in the dict   DICTIONARY     a    valueA    b    valueB    c    valueC    d    valueD   keys     a    l    c    def remove keys key       try          DICTIONARY pop key  None      except          pass    or do any action  list map remove key  keys   print DICTIONARY    output   DICTIONARY     b    valueB    d    valueD

User · Answer

inline  import functools     not key c  in d d     a    avalue    b    bvalue    d    dvalue    entitiesToREmove     a    b    c       python2 map lambda x  functools partial d pop  x  None     entitiesToREmove      python3  list map lambda x  functools partial d pop  x  None     entitiesToREmove    print d    output    d    dvalue

User · Answer

Another map   way to remove list of keys from dictionary and avoid raising KeyError exception     dic              key1   1           key2   2           key3   3           key4   4           key5   5             keys to remove     key not exist    key1    key2    key3   k   list map dic pop  keys to remove  keys to remove    print  k    k  print  dic after     n   dic     this will produce output     k    key not exist   1  2  3  dic after      key4   4   key5   5   Duplicate keys to remove is artificial  it needs to supply defaults values for dict pop   function  You can add here any array with len    len key to remove   For example dic          key1   1       key2   2       key3   3       key4   4       key5   5     keys to remove     key not exist    key1    key2    key3       k   list map dic pop  keys to remove  np zeros len keys to remove      print  k    k  print  dic after      dic      will produce output    k   0 0  1  2  3  dic after      key4   4   key5   5

[python] Removing multiple keys from a dictionary safely

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