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eb393e9 Feb 18, 2015
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############ HashTable helper functions
def hash_function(key_str, size):
return sum([ord(c) for c in key_str]) % size
############ HashTable class
class HashTable:
""" Hash table which uses strings for keys. Value can be any object.
Example usage:
ht = HashTable(10)
ht.set('a', 1).set('b', 2).set('c', 3)
ht['c'] = 30
def __init__(self, capacity=1000):
""" Capacity defaults to 1000. """
self.capacity = capacity
self.size = 0
self._keys = []
# Storage format: [ [ [key1, value], [key2, value] ], [ [key3, value] ] ]
# The outmost list is the one which the hash function maps the index to. The next inner
# Array is the list of objects in that storage cell. The 3rd level is the individual
# item array, where the 1st item is the key, and the 2nd item is the value. = [[] for _ in range(capacity)]
def _find_by_key(self, key, find_result_func):
index = hash_function(key, self.capacity)
hash_table_cell =[index]
found_item = None
for item in hash_table_cell:
if item[0] == key:
found_item = item
return find_result_func(found_item, hash_table_cell)
def set(self, key, obj):
""" Insert object with key into hash table. If key already exists, then the object will be
updated. Key must be a string. Returns self. """
def find_result_func(found_item, hash_table_cell):
if found_item:
found_item[1] = obj
hash_table_cell.append([key, obj])
self.size += 1
self._find_by_key(key, find_result_func)
return self
def get(self, key):
""" Get object with key (key must be a string). If not found, it will raise a KeyError. """
def find_result_func(found_item, _):
if found_item:
return found_item[1]
raise KeyError(key)
return self._find_by_key(key, find_result_func)
def remove(self, key):
""" Remove the object associated with key from the hashtable. If found, the object will
be returned. If not found, KeyError will be raised. """
def find_result_func(found_item, hash_table_cell):
if found_item:
self.size -= 1
return found_item[1]
raise KeyError(key)
return self._find_by_key(key, find_result_func)
####### Python's dict interface
def keys(self):
return self._keys
def __setitem__(self, key, value):
self.set(key, value)
def __getitem__(self, key):
return self.get(key)
def __delitem__(self, key):
return self.remove(key)
def __repr__(self):
return '{ ' + ', '.join([key + ':' + str(self.get(key)) for key in self._keys]) + ' }'
if __name__ == "__main__":
# Run unit tests
import unittest
testsuite = unittest.TestLoader().discover('test', pattern="*hashtable*")