Python dictionary TypeError unhashable type list

Question

I m having troubles in populating a python dictionary starting from another dictionary   Let s assume that the  source  dictionary has string as keys and has a list of custom objects per value   I m creating my target dictionary exactly as I have been creating my  source  dictionary how is it possible this is not working    I get   TypeError  unhashable type   list    Code    aTargetDictionary      for aKey in aSourceDictionary      aTargetDictionary aKey           aTargetDictionary aKey  extend aSourceDictionary aKey     The error is on this line   aTargetDictionary aKey

User · Answer

This is indeed rather odd   If aSourceDictionary were a dictionary  I don t believe it is possible for your code to fail in the manner you describe   This leads to two hypotheses    The code you re actually running is not identical to the code in your question  perhaps an earlier or later version   aSourceDictionary is in fact not a dictionary  but is some other structure  for example  a list

User · Answer

You can also use defaultdict to address this situation  It goes something like this  from collections import defaultdict   initialises the dictionary with values as list aTargetDictionary   defaultdict list   for aKey in aSourceDictionary      aTargetDictionary aKey  append aSourceDictionary aKey

User · Answer

It works fine   http   codepad org 5KgO0b1G  your aSourceDictionary variable may have other datatype than dict  aSourceDictionary      abc     1 2 3     ccd     4 5    aTargetDictionary      for aKey in aSourceDictionary          aTargetDictionary aKey               aTargetDictionary aKey  extend aSourceDictionary aKey   print aTargetDictionary

User · Answer

The error you gave is due to the fact that in python  dictionary keys must be immutable types  if key can change  there will be problems   and list is a mutable type   Your error says that you try to use a list as dictionary key  you ll have to change your list into tuples if you want to put them as keys in your dictionary   According to the python doc        The only types of values not acceptable as keys are values containing   lists or dictionaries or other mutable types that are compared by   value rather than by object identity  the reason being that the   efficient implementation of dictionaries requires a key   s hash value   to remain constant

User · Answer

As per your description  things don t add up  If aSourceDictionary is a dictionary  then your for loop has to work properly    gt  gt  gt  source     a    1  2    b    2  3    gt  gt  gt  target       gt  gt  gt  for key in source        target key             target key  extend source key         gt  gt  gt  target   a    1  2    b    2  3    gt  gt  gt

[python] Python dictionary : TypeError: unhashable type: 'list'

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