Hash Map in Python

Question

I want to implement a HashMap in Python   I want to ask a user for an input  depending on his input I am retrieving some information from the HashMap  If the user enters a key of the HashMap   I would like to retrieve the corresponding value   How do I implement this functionality in Python   HashMap lt String String gt  streetno new HashMap lt String String gt        streetno put  1    Sachin Tendulkar       streetno put  2    Dravid       streetno put  3   Sehwag       streetno put  4   Laxman       streetno put  5   Kohli

User · Answer

Here is the implementation of the Hash Map using python For the simplicity hash map is of a fixed size 16. This can be changed easily. Rehashing is out of scope of this code.

class Node:
    def __init__(self, key, value):
        self.key = key
        self.value = value
        self.next = None

class HashMap:
    def __init__(self):
        self.store = [None for _ in range(16)]
    def get(self, key):
        index = hash(key) & 15
        if self.store[index] is None:
            return None
        n = self.store[index]
        while True:
            if n.key == key:
                return n.value
            else:
                if n.next:
                    n = n.next
                else:
                    return None
    def put(self, key, value):
        nd = Node(key, value)
        index = hash(key) & 15
        n = self.store[index]
        if n is None:
            self.store[index] = nd
        else:
            if n.key == key:
                n.value = value
            else:
                while n.next:
                    if n.key == key:
                        n.value = value
                        return
                    else:
                        n = n.next
                n.next = nd

hm = HashMap()
hm.put("1", "sachin")
hm.put("2", "sehwag")
hm.put("3", "ganguly")
hm.put("4", "srinath")
hm.put("5", "kumble")
hm.put("6", "dhoni")
hm.put("7", "kohli")
hm.put("8", "pandya")
hm.put("9", "rohit")
hm.put("10", "dhawan")
hm.put("11", "shastri")
hm.put("12", "manjarekar")
hm.put("13", "gupta")
hm.put("14", "agarkar")
hm.put("15", "nehra")
hm.put("16", "gawaskar")
hm.put("17", "vengsarkar")
print(hm.get("1"))
print(hm.get("2"))
print(hm.get("3"))
print(hm.get("4"))
print(hm.get("5"))
print(hm.get("6"))
print(hm.get("7"))
print(hm.get("8"))
print(hm.get("9"))
print(hm.get("10"))
print(hm.get("11"))
print(hm.get("12"))
print(hm.get("13"))
print(hm.get("14"))
print(hm.get("15"))
print(hm.get("16"))
print(hm.get("17"))

Output:

sachin
sehwag
ganguly
srinath
kumble
dhoni
kohli
pandya
rohit
dhawan
shastri
manjarekar
gupta
agarkar
nehra
gawaskar
vengsarkar

User · Answer

Python dictionary is a built-in type that supports key-value pairs   streetno     1    Sachin Tendulkar    2    Dravid    3    Sehwag    4    Laxman    5    Kohli     as well as using the dict keyword   streetno   dict   1    Sachin Tendulkar    2    Dravid       or   streetno      streetno  1      Sachin Tendulkar

User · Answer

streetno     1    Sachin Tendulkar               2    Dravid               3    Sehwag               4    Laxman               5    Kohli      And to retrieve values   name   streetno get 3   default value     Or  name   streetno 3    That s using number as keys  put quotes around the numbers to use strings as keys

User · Answer

All you wanted  at the time the question was originally asked  was a hint  Here s a hint  In Python  you can use dictionaries

User · Answer

In python you would use a dictionary   It is a very important type in python and often used   You can create one easily by  name        Dictionaries have many methods     add entries   gt  gt  gt  name  first      John   gt  gt  gt  name  second      Doe   gt  gt  gt  name   first    John    second    Doe      you can store all objects and datatypes as value in a dictionary   as key you can use all objects and datatypes that are hashable  gt  gt  gt  name  list       list    inside    dict    gt  gt  gt  name 1    1  gt  gt  gt  name   first    John    second    Doe   1  1   list     list    inside    dict      You can not influence the order of a dict

User · Answer

Python Counter is also a good option in this case   from collections import Counter  counter   Counter   Sachin Tendulkar    Sachin Tendulkar    other things     print counter    This returns a dict with the count of each element in the list   Counter   Sachin Tendulkar   2   other things   1

User · Answer

Hash maps are built-in in Python  they re called dictionaries   streetno                              create a dictionary called streetno streetno  1      Sachin Tendulkar     assign value to key  1    Usage    1  in streetno                       check if key  1  is in streetno streetno  1                           get the value from key  1    See the documentation for more information  e g  built-in methods and so on  They re great  and very common in Python programs  unsurprisingly

User · Answer

class HashMap      def   init   self           self size   64         self map    None    self size      def  get hash self  key           hash   0          for char in str key               hash    ord char          return hash   self size      def add self  key  value           key hash   self  get hash key          key value    key  value           if self map key hash  is None              self map key hash    list  key value               return True         else              for pair in self map key hash                   if pair 0     key                      pair 1    value                     return True                 else                      self map key hash  append list  key value                        return True      def get self  key           key hash   self  get hash key          if self map key hash  is not None              for pair in self map key hash                    if pair 0     key                      return pair 1          return None      def delete self  key           key hash   self  get hash key           if self map key hash  is None               return False         for i in range 0  len self map key hash                 if self map key hash  i  0     key                  self map key hash  pop i                  return True      def print self            print  ---Phonebook---           for item in self map              if item is not None                  print str item    h   HashMap

User · Answer

It s built-in for Python  See dictionaries   Based on your example   streetno     1    Sachine Tendulkar                2    Dravid                3    Sehwag                4    Laxman                5    Kohli      You could then access it like so   sachine   streetno  1     Also worth mentioning  it can use any non-mutable data type as a key  That is  it can use a tuple  boolean  or string as a key

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