1. The Map/Dictionary abstract data type (ADT) stores key-value pairs. The key is used to look up the data value.
Returns a string representation of the dictionary
__s
tr
__(self
)
str(d)
Returns the number of items in the dictionary
__len__(self)len(d)
Iterates over the keys in the dictionary
__iter__(self)for k in d:
Return
True
if
key
is in the dictionary; return
False
otherwise
__contains__(self,key)if ”Name” in d:
Removes the entry associated with
key
__
del
item__(self,
key)
d
el
d
[”Name”]
Given a
key
return it value or
None
if
key
is not
in the dictionary
__
g
etitem__(self,
key)
temp =
d[”Name”]
Inserts a key-value entry if
key
does not exist or
replaces the old value with
value
if
key
exists.
__setitem__(self,
key,value)
d[”Name”]
= “Bob”
Constructs an empty dictionary
__init__(self)d = ListDict()
DescriptionClass NameMethod call
a) Complete the code for the
__contains__
method.
def __contains__(self, key):
b) Complete the code for the
__setitem__
method.
def __setitem__(self, key, value):
Data Structures Lecture 15 Name:__________________
Lecture 15 Page 1
from entry import Entry
class ListDict(object):
"""Dictionary implemented with a Python list."""
def __init__(self):
self._table = []
def __getitem__(self, key):
"""Returns the value associated with key or
returns None if key does not exist."""
entry = Entry(key, None)
try:
index = self._table.index(entry)
return self._table[index].getValue()
except:
return None
def __delitem__(self, key):
"""Removes the entry associated with key."""
entry = Entry(key, None)
try:
index = self._table.index(entry)
self._table.pop(index)
except:
return
def __str__(self):
"""Returns string repr. of the dictionary"""
resultStr = "{"
for item in self._table:
resultStr = resultStr + " " + str(item)
return resultStr + " }"
def __iter__(self):
"""Iterates over keys of the dictionary"""
for item in self._table:
yield item.getKey()
raise StopIteration
ListDict
object
_table
_key _value
. . .
012345
Python list object
Entry object
Name Bob
class Entry(object):
"""A key/value pair."""
def __init__(self, key, value):
self._key = key
self._value = value
def getKey(self):
return self._key
def getValue(self):
return self._value
def setValue(self, newValue):
self._value = newValue
def __eq__(self, other):
if not isinstance(other, Entry):
return False
return self._key == other._key
def __str__(self):
return str(self._key) + ":" + str(self._value)
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