How to set default value to all keys of a dict object in python

Question

I know you can use setdefault key  value  to set default value for a given key  but is there a way to set default values of all keys to some value after creating a dict    Put it another way  I want the dict to return the specified default value for every key I didn t yet set

User · Answer

You can use the following class  Just change zero to any default value you like  The solution was tested in Python 2 7   class cDefaultDict dict         dictionary that returns zero for missing keys       keys with zero values are not stored      def   missing   self key           return 0      def   setitem   self  key  value           if value  0              if key in self     returns zero anyway  so no need to store it                 del self key          else              dict   setitem   self  key  value

User · Answer

Not after creating it  no  But you could use a defaultdict in the first place  which sets default values when you initialize it

User · Answer

Use defaultdict  from collections import defaultdict a       a   defaultdict lambda 0 a  a  anything       gt  0   This is very useful for case like this where default values for every key is set as 0   results     pre-access      count   4   pass count   2   no-access      count   55   pass count   19  for k v in results iteritems      a  count      v  count     a  pass count      v  pass count

User · Answer

Is this what you want    gt  gt  gt  d   a  1  b  2  c  3   gt  gt  gt  default val 99  gt  gt  gt  for k in d          d k  default val           gt  gt  gt  d   a   99   b   99   c   99   gt  gt  gt     gt  gt  gt  d   a  1  b  2  c  3   gt  gt  gt  from collections import defaultdict  gt  gt  gt  d defaultdict lambda 99 d   gt  gt  gt  d defaultdict  lt function  lt lambda gt  at 0x03D21630 gt     a   1   c   3   b   2    gt  gt  gt  d 3  99

User · Answer

In case you actually mean what you seem to ask  I ll provide this alternative answer   You say you want the dict to return a specified value  you do not say you want to set that value at the same time  like defaultdict does  This will do so   class DictWithDefault dict       def   init   self  default    kwargs           self default   default         super DictWithDefault  self    init     kwargs       def   getitem   self  key           if key in self              return super DictWithDefault  self    getitem   key          return self default   Use like this   d   DictWIthDefault 99  x 5  y 3  print d  x       5 print d 42       99 42 in d          False d 42    3 42 in d          True   Alternatively  you can use a standard dict like this   d    3  9  4  2  default   99 print d get 3  default     9 print d get 42  default    99

User · Answer

defaultdict can do something like that for you   Example    gt  gt  gt  from collections import defaultdict  gt  gt  gt  d   defaultdict list   gt  gt  gt  d defaultdict  lt class  list  gt        gt  gt  gt  d  new   append 10   gt  gt  gt  d defaultdict  lt class  list  gt     new    10

User · Answer

You can replace your old dictionary with a defaultdict    gt  gt  gt  from collections import defaultdict  gt  gt  gt  d     foo   123   bar   456   gt  gt  gt  d  baz   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  KeyError   baz   gt  gt  gt  d   defaultdict lambda  -1  d   gt  gt  gt  d  baz   -1   The  trick  here is that a defaultdict can be initialized with another dict  This means  that you preserve the existing values in your normal dict    gt  gt  gt  d  foo   123

[python] How to set default value to all keys of a dict object in python?

Examples related to python

Examples related to dictionary