How to create a trie in Python

Question

I m interested in tries and DAWGs  direct acyclic word graph  and I ve been reading a lot about them but I don t understand what should the output trie or DAWG file look like    Should a trie be an object of nested dictionaries  Where each letter is divided in to letters and so on  Would a lookup performed on such a dictionary be fast if there are 100k or 500k entries  How to implement word-blocks consisting of more than one word separated with - or space  How to link prefix or suffix of a word to another part in the structure   for DAWG    I want to understand the best output structure in order to figure out how to create and use one   I would also appreciate what should be the output of a DAWG along with trie   I do not want to see graphical representations with bubbles linked to each other  I want to know the output object once a set of words are turned into tries or DAWGs

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Have a look at this   https   github com kmike marisa-trie     Static memory-efficient Trie structures for Python  2 x and 3 x        String data in a MARISA-trie may take up to 50x-100x less memory than   in a standard Python dict  the raw lookup speed is comparable  trie   also provides fast advanced methods like prefix search       Based on marisa-trie C   library    Here s a blog post from a company using marisa trie successfully  https   www repustate com blog sharing-large-data-structure-across-processes-python      At Repustate  much of our data models we use in our text analysis can be represented as simple key-value pairs  or dictionaries in Python lingo  In our particular case  our dictionaries are massive  a few hundred MB each  and they need to be accessed constantly  In fact for a given HTTP request  4 or 5 models might be accessed  each doing 20-30 lookups  So the problem we face is how do we keep things fast for the client as well as light as possible for the server                 I found this package  marisa tries  which is a Python wrapper around a C   implementation of a marisa trie     Marisa    is an acronym for Matching Algorithm with Recursively Implemented StorAge  What   s great about marisa tries is the storage mechanism really shrinks how much memory you need  The author of the Python plugin claimed 50-100X reduction in size     our experience is similar       What   s great about the marisa trie package is that the underlying trie structure can be written to disk and then read in via a memory mapped object  With a memory mapped marisa trie  all of our requirements are now met  Our server   s memory usage went down dramatically  by about 40   and our performance was unchanged from when we used Python   s dictionary implementation    There are also a couple of pure-python implementations  though unless you re on a restricted platform you d want to use the C   backed implementation above for best performance    https   github com bdimmick python-trie https   pypi python org pypi PyTrie

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If you want a TRIE implemented as a Python class  here is something I wrote after reading about them   class Trie       def   init   self           self   final   False         self   nodes           def   repr   self           return  Trie lt len     final    gt   format len self   self   final       def   getstate   self           return self   final  self   nodes      def   setstate   self  state           self   final  self   nodes   state      def   len   self           return len self   nodes       def   bool   self           return self   final      def   contains   self  array           try              return self array          except KeyError              return False      def   iter   self           yield self         for node in self   nodes values                yield from node      def   getitem   self  array           return self   get array  False       def create self  array           self   get array  True    final   True      def read self           yield from self   read          def update self  array           self array    final   True      def delete self  array           self array    final   False      def prune self           for key  value in tuple self   nodes items                 if not value prune                    del self   nodes key          if not len self               self delete             return self      def   get self  array  create           if array              head   tail   array             if create and head not in self   nodes                  self   nodes head    Trie               return self   nodes head    get tail  create          return self      def   read self  name           if self   final              yield name         for key  value in self   nodes items                yield from value   read name    key

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class Trie      head           def add self word            cur   self head         for ch in word              if ch not in cur                  cur ch                   cur   cur ch          cur        True      def search self word           cur   self head         for ch in word              if ch not in cur                  return False             cur   cur ch           if     in cur              return True         else              return False     def printf self           print  self head   dictionary   Trie   dictionary add  hi    dictionary add  hello    dictionary add  eye    dictionary add  hey     print dictionary search  hi    print dictionary search  hello    print dictionary search  hel    print dictionary search  he    dictionary printf     Out  True False False False   h     i         True

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from collections import defaultdict   Define Trie    trie   lambda  defaultdict  trie    Create Trie   trie    trie   for s in   cat    bat    rat    cam        curr   trie     for c in s          curr   curr c      curr setdefault   end     Lookup   def word exist trie  word       curr   trie     for w in word          if w not in curr              return False         curr   curr w      return   end  in curr   Test   print word exist trie   cam

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This is much like a previous answer but simpler to read  def make trie words       trie          for word in words          head   trie         for char in word              if char not in head                  head char                   head   head char          head  quot  end  quot      quot  end  quot      return trie

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Unwind is essentially correct that there are many different ways to implement a trie  and for a large  scalable trie  nested dictionaries might become cumbersome -- or at least space inefficient  But since you re just getting started  I think that s the easiest approach  you could code up a simple trie in just a few lines  First  a function to construct the trie    gt  gt  gt   end     end    gt  gt  gt    gt  gt  gt  def make trie  words           root   dict           for word in words              current dict   root             for letter in word                  current dict   current dict setdefault letter                  current dict  end     end         return root       gt  gt  gt  make trie  foo    bar    baz    barz     b     a     r      end      end     z      end      end                     z      end      end          f     o     o      end      end         If you re not familiar with setdefault  it simply looks up a key in the dictionary  here  letter or  end   If the key is present  it returns the associated value  if not  it assigns a default value to that key and returns the value     or  end    It s like a version of get that also updates the dictionary     Next  a function to test whether the word is in the trie    gt  gt  gt  def in trie trie  word           current dict   trie         for letter in word              if letter not in current dict                  return False             current dict   current dict letter          return  end in current dict       gt  gt  gt  in trie make trie  foo    bar    baz    barz     baz   True  gt  gt  gt  in trie make trie  foo    bar    baz    barz     barz   True  gt  gt  gt  in trie make trie  foo    bar    baz    barz     barzz   False  gt  gt  gt  in trie make trie  foo    bar    baz    barz     bart   False  gt  gt  gt  in trie make trie  foo    bar    baz    barz     ba   False   I ll leave insertion and removal to you as an exercise   Of course  Unwind s suggestion wouldn t be much harder  There might be a slight speed disadvantage in that finding the correct sub-node would require a linear search  But the search would be limited to the number of possible characters -- 27 if we include  end  Also  there s nothing to be gained by creating a massive list of nodes and accessing them by index as he suggests  you might as well just nest the lists   Finally  I ll add that creating a directed acyclic word graph  DAWG  would be a bit more complex  because you have to detect situations in which your current word shares a suffix with another word in the structure  In fact  this can get rather complex  depending on how you want to structure the DAWG  You may have to learn some stuff about Levenshtein distance to get it right

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This version is using recursion   import pprint from collections import deque  pp   pprint PrettyPrinter indent 4   inp   raw input  Enter a sentence to show as trie n   words   inp split      trie        def trie recursion trie ds  word       try          letter   word popleft           out   trie recursion trie ds get letter       word      except IndexError            End of the word         return           Dont update if letter already present     if not trie ds has key letter           trie ds letter    out      return trie ds  for word in words        Go through each word     trie   trie recursion trie  deque word    pprint pprint trie    Output   Coool  lt algos gt   python trie py Enter a sentence to show as trie foo bar baz fun      b          a            r              z                    f          o            o                  u            n

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Here is a list of python packages that implement Trie    marisa-trie - a C   based implementation  python-trie - a simple pure python implementation  PyTrie - a more advanced pure python implementation  pygtrie - a pure python implementation by Google  datrie - a double array trie implementation based on libdatrie

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Modified from senderle s method  above   I found that Python s defaultdict is ideal for creating a trie or a prefix tree   from collections import defaultdict  class Trie              Implement a trie with insert  search  and startsWith methods              def   init   self           self root   defaultdict           param  string  word        return  void        Inserts a word into the trie      def insert self  word           current   self root         for letter in word              current   current setdefault letter              current setdefault   end           param  string  word        return  boolean        Returns if the word is in the trie      def search self  word           current   self root         for letter in word              if letter not in current                  return False             current   current letter          if   end  in current              return True         return False         param  string  prefix        return  boolean        Returns if there is any word in the trie       that starts with the given prefix      def startsWith self  prefix           current   self root         for letter in prefix              if letter not in current                  return False             current   current letter          return True    Now test the class  test   Trie   test insert  helloworld   test insert  ilikeapple   test insert  helloz    print test search  hello   print test startsWith  hello   print test search  ilikeapple

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There s no  should   it s up to you  Various implementations will have different performance characteristics  take various amounts of time to implement  understand  and get right  This is typical for software development as a whole  in my opinion   I would probably first try having a global list of all trie nodes so far created  and representing the child-pointers in each node as a list of indices into the global list  Having a dictionary just to represent the child linking feels too heavy-weight  to me

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Python Class for Trie  Trie Data Structure can be used to store data in O L  where L is the length of the string so for inserting N strings time complexity would be O NL  the string can be searched in O L  only same goes for deletion  Can be clone from https   github com Parikshit22 pytrie git class Node      def   init   self           self children    None  26         self isend   False          class trie      def   init   self            self   root   Node                def   len   self            return len self search byprefix               def   str   self           ll    self search byprefix             string              for i in ll              string  i             string    n          return string              def chartoint self character           return ord character -ord  a            def remove self string           ptr   self   root         length   len string          for idx in range length               i   self chartoint string idx               if ptr children i  is not None                  ptr   ptr children i              else                  raise ValueError  quot Keyword doesn t exist in trie quot           if ptr isend is not True              raise ValueError  quot Keyword doesn t exist in trie quot           ptr isend   False         return          def insert self string           ptr   self   root         length   len string          for idx in range length               i   self chartoint string idx               if ptr children i  is not None                  ptr   ptr children i              else                  ptr children i    Node                   ptr   ptr children i          ptr isend   True              def search self string           ptr   self   root         length   len string          for idx in range length               i   self chartoint string idx               if ptr children i  is not None                  ptr   ptr children i              else                  return False         if ptr isend is not True              return False         return True          def   getall self ptr key key list           if ptr is None              key list append key              return         if ptr isend  True              key list append key          for i in range 26               if ptr children i   is not None                  self   getall ptr children i  key chr ord  a   i  key list               def search byprefix self key           ptr   self   root         key list              length   len key          for idx in range length               i   self chartoint key idx               if ptr children i  is not None                  ptr   ptr children i              else                  return None                  self   getall ptr key key list          return key list            t   trie   t insert  quot shubham quot   t insert  quot shubhi quot   t insert  quot minhaj quot   t insert  quot parikshit quot   t insert  quot pari quot   t insert  quot shubh quot   t insert  quot minakshi quot    print t search  quot minhaj quot    print t search  quot shubhk quot    print t search byprefix  m    print len t   print t remove  quot minhaj quot    print t    Code Oputpt True  False    minakshi    minhaj    7  minakshi  minhajsir  pari  parikshit  shubh  shubham  shubhi

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Using defaultdict and reduce function   Create Trie  from functools import reduce from collections import defaultdict T   lambda   defaultdict T  trie   T   reduce dict   getitem    how  trie   isEnd     True  Trie   defaultdict  lt function   main    lt lambda gt    gt                 h   defaultdict  lt function   main    lt lambda gt    gt                              o   defaultdict  lt function   main    lt lambda gt    gt                                           w   defaultdict  lt function   main    lt lambda gt    gt                                                        isEnd   True           Search In Trie    curr   trie for w in  how       if w in curr          curr   curr w      else          print  quot Not Found quot           break if curr  isEnd        print  Found

[python] How to create a trie in Python

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