Understanding get method in Python

Question

sentence    The quick brown fox jumped over the lazy dog   characters       for character in sentence      characters character    characters get character  0    1   print characters    I don t understand what characters get character  0    1 is doing  rest all seems pretty straightforward

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The get method of a dict  like for example characters  works just like indexing the dict  except that  if the key is missing  instead of raising a KeyError it returns the default value  if you call  get with just one argument  the key  the default value is None    So an equivalent Python function  where calling myget d  k  v  is just like d get k  v  might be   def myget d  k  v None     try  return d k    except KeyError  return v   The sample code in your question is clearly trying to count the number of occurrences of each character  if it already has a count for a given character  get returns it  so it s just incremented by one   else get returns 0  so the incrementing correctly gives 1 at a character s first occurrence in the string

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To understand what is going on  let s take one letter repeated more than once  in the sentence string and follow what happens when it goes through the loop    Remember that we start off with an empty characters dictionary   characters        I will pick the letter  e   Let s pass the character  e   found in the word The  for the first time through the loop  I will assume it s the first character to go through the loop and I ll substitute the variables with their values   for  e  in  The quick brown fox jumped over the lazy dog            e        get  e   0    1    characters get  e   0  tells python to look for the key  e  in the dictionary  If it s not found it returns 0  Since this is the first time  e  is passed through the loop  the character  e  is not found in the dictionary yet  so the get method returns 0  This 0 value is then added to the 1  present in the characters character    characters get character 0    1 equation   After completion of the first loop using the  e  character  we now have an entry in the dictionary like this    e   1   The dictionary is now    characters     e   1    Now  let s pass the second  e   found in the word jumped  through the same loop  I ll assume it s the second character to go through the loop and I ll update the variables with their new values   for  e  in  The quick brown fox jumped over the lazy dog          e   1   e       e   1  get  e   0    1   Here the get method finds a key entry for  e  and finds its value which is 1   We add this to the other 1 in characters get character  0    1 and get 2 as result   When we apply this in the characters character    characters get character  0    1 equation   characters  e     2   It should be clear that the last equation assigns a new value 2 to the already present  e  key   Therefore the dictionary is now    characters     e   2

User · Answer

If d is a dictionary  then d get k  v  means  give me the value of k in d  unless k isn t there  in which case give me v   It s being used here to get the current count of the character  which should start at 0 if the character hasn t been encountered before

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Start here http   docs python org tutorial datastructures html dictionaries Then here http   docs python org library stdtypes html mapping-types-dict Then here http   docs python org library stdtypes html dict get characters get  key  default    key is a character  default is 0  If the character is in the dictionary  characters  you get the dictionary object  If not  you get 0   Syntax   get key   default   Return the value for key if key is in the dictionary  else default  If default is not given  it defaults to None  so that this method never raises a KeyError

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I see this is a fairly old question  but this looks like one of those times when something s been written without knowledge of a language feature  The collections library exists to fulfill these purposes   from collections import Counter letter counter   Counter   for letter in  The quick brown fox jumps over the lazy dog       letter counter letter     1   gt  gt  gt  letter counter Counter       8   o   4   e   3   h   2   r   2   u   2   T   1   a   1   c   1   b   1   d   1   g   1   f   1   i   1   k   1   j   1   m   1   l   1   n   1   q   1   p   1   s   1   t   1   w   1   v   1   y   1   x   1   z   1     In this example the spaces are being counted  obviously  but whether or not you want those filtered is up to you   As for the dict get a key  default value   there have been several answers to this particular question -- this method returns the value of the key  or the default value you supply  The first argument is the key you re looking for  the second argument is the default for when that key is not present

[python] Understanding .get() method in Python

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