How do I make a dictionary with multiple keys to one value

Question

I have a question about a dictionary I want to make  My goal is to have multiple keys to a single value  like below   dictionary      a    b    1    c    d    2  assert dictionary  a      1 assert dictionary  b      1   Any ideas

User · Answer

I guess you mean this   class Value      def   init   self  v None           self v   v  v1   Value 1  v2   Value 2   d     a   v1   b   v1   c   v2   d   v2  d  a   v    1  d  b   v    2   True    Python s strings and numbers are immutable objects   So  if you want d  a   and d  b   to point to the same value that  updates  as it changes  make the value refer to a mutable object  user-defined class like above  or a dict  list  set   Then  when you modify the object at d  a    d  b   changes at same time because they both point to same object

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If you re going to be adding to this dictionary frequently you d want to take a class based approach  something similar to  Latty s answer in this SO question 2d-dictionary-with-many-keys-that-will-return-the-same-value    However  if you have a static dictionary  and you need only access values by multiple keys then you could just go the very simple route of using two dictionaries  One to store the alias key association and one to store your actual data   alias          a    id1        b    id1        c    id2        d    id2     dictionary          id1   1       id2   2    dictionary alias  a      If you need to add to the dictionary you could write a function like this for using both dictionaries   def add key  id  value None      if id in dictionary          if key in alias                Do nothing             pass         else              alias key    id     else          dictionary id    value         alias key    id  add  e    id2   add  f    id3   3    While this works  I think ultimately if you want to do something like this writing your own data structure is probably the way to go  though it could use a similar structure

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It is simple  The first thing that you have to understand the design of the Python interpreter  It doesn t allocate memory for all the variables basically if any two or more variable has the same value it just map to that value    let s go to the code example   In  6   a   10  In  7   id a  Out 7   10914656  In  8   b   10  In  9   id b  Out 9   10914656  In  10   c   11  In  11   id c  Out 11   10914688  In  12   d   21  In  13   id d  Out 13   10915008  In  14   e   11  In  15   id e  Out 15   10914688  In  16   e   21  In  17   id e  Out 17   10915008  In  18   e is d Out 18   True In  19   e   30  In  20   id e  Out 20   10915296   From the above output  variables a and b shares the same memory  c and d has different memory when I create a new variable e and store a value  11  which is already present in the variable c so it mapped to that memory location and doesn t create a new memory when I change the value present in the variable e to 21 which is already present in the variable d so now variables d and e share the same memory location  At last  I change the value in the variable e to 30 which is not stored in any other variable so it creates a new memory for e   so any variable which is having same value shares the memory      Not for list and dictionary objects   let s come to your question   when multiple keys have same value then all shares same memory so the thing that you expect is already there in python   you can simply use it like this  In  49   dictionary                   k1  1                k2  1                k3  2                k4  2                               In  50   id dictionary  k1    Out 50   10914368  In  51   id dictionary  k2    Out 51   10914368  In  52   id dictionary  k3    Out 52   10914400  In  53   id dictionary  k4    Out 53   10914400   From the above output  the key k1 and k2 mapped to the same address which means value one stored only once in the memory which is multiple key single value dictionary this is the thing you want    P

User · Answer

Your example creates multiple key  value pairs if using fromkeys  If you don t want this  you can use one key and create an alias for the key  For example if you are using a register map  your key can be the register address and the alias can be register name  That way you can perform read write operations on the correct register     gt  gt  gt  mydict       gt  gt  gt  mydict  1 2      30  20   gt  gt  gt  alias1    1 2   gt  gt  gt  print mydict alias1   30  20   gt  gt  gt  mydict  1 3      30  30   gt  gt  gt  print mydict   1  2    30  20    1  3    30  30    gt  gt  gt  alias1 in mydict True

[python] How do I make a dictionary with multiple keys to one value?

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