python advanced data structure dictionary with examples python advanced data structure dictionary with examples

Introduction to
Dictionaries
• Pair of items
• Each pair has key and value
• Keys should be unique
• Key and value are separated
by :
• Each pair is separated by ,
Example:
dict = {‘Alice’ : 1234, ‘Bob’ :

Properties of
Dictionaries
• Unordered mutable collections
• Items are stored and fetched by key
• Accessed by key, not offset position
• Unordered collections of arbitrary objects
• Variable-length, heterogeneous, and arbitrarily
nestable

Creating a
Dictionary
Creating an EMPTY
dictionary
dictname =
{}
Example:
Dict1 = {}
MyDict =
{} Books
= {}
Creating a dictionary with
items
dictname = {key1:val1,
key2:val2, ….}
Example:
MyDict = { 1 : ‘Chocolate’, 2 : ‘Icecream’}
MyCourse = {‘MS’ : ‘Python’, ‘IT’ : ‘C’, ‘CSE’ : ‘C++’, ‘MCA’ :
‘Java’}
MyCircle = {‘Hubby’:9486028245, ‘Mom’:9486301601}

Accessing
Values
Using keys within square
brackets
>>> print MyDict[1]
‘Chocolate’
>>> print MyCourse[‘CSE’]
‘C++’

Updating
Elements
• Update by adding a new item (key-
value) pair
• Modify an existing entry
>>> MyDict[1] = ‘Pizza’
>>> MyCourse[‘MCA’] = ‘UML’

Deleting
Elements
• remove an element in a dictionary using
the key
>>> del MyCourse[‘IT’]
• remove all the elements
>>> MyCourse.clear()
• delete the dictionary
>>> del MyCourse

Basic
Operations
>>> D = {'spam': 2, 'ham': 1,
'eggs': 3}
>>>
len(D)
# Number of entries in
dictionary 3
>>> 'ham' in
D
# Key membership
test
Tru
e
>>>
list(D.keys())
# Create a new list of D's
keys
['eggs', 'spam',
'ham']

Basic
Operations
# A key that is
there
# A key that is
missing
>>> list(D.values())
[3, 2, 1]
>>> list(D.items())
[('eggs', 3), ('spam', 2),
('ham', 1)]
>>> D.get('spam')
2
>>> print(D.get('toast'))
None

Update
Method
>>> D
{'eggs': 3, 'spam': 2,
'ham': 1}
>>> D2 = {'toast':4,
'muffin':5}
>>> D.update(D2)
>>> D
{'eggs': 3, 'muffin': 5, 'toast': 4, 'spam': 2,
'ham': 1}
#unordere
d

POP
Method
Delete and return value for a given key
>>> D = {'eggs': 3, 'muffin': 5, 'toast': 4, 'spam': 2,
'ham': 1}
>>> D.pop('muffin')
5
>>> D.pop('toast‘)
4
>>> D
{'eggs': 3, 'spam': 2, 'ham': 1}

List vs
Dictionary
>>> L =
[]
>>> L[99] =
'spam’
IndexError: list assignment index out of
range
>>>D = {}
>>> D[99] =
'spam'
>>> D[99]
'spam'
>>> D {99:

Nesting in
dictionaries
>>> jobs = []
>>>
jobs.append('developer')
>>>
jobs.append(‘manager‘)
# jobs = [‘developer’,
‘manager’]
rec = {}
>>> rec['name'] = 'Bob'
>>> rec['age'] = 40
>>> rec['job'] = jobs
>>> rec
{'name': 'Bob', 'age': 40, 'job': ['developer',
'manager']}

>>> rec['name']
'Bob'
>>> rec['job']
['developer',
'manager']
>>> rec['job'][1]
'manager’

Other Ways to Make
Dictionaries
D = {'name': 'Bob', 'age':
40}
D =
{}
# Assign by keys
dynamically
D['name'] = 'Bob'
D['age'] = 40
# Creating a dictionary by
assignment
dict(name='Bob', age=40)
# Creating dictionary with tuples
form dict([('name', 'Bob'), ('age',

Comprehensions in
Dictionaries
>>> D = {k: v for (k, v) in zip(['a', 'b', 'c'], [1,
2, 3])}
>>> D
{'a': 1, 'b': 2, 'c': 3}
>>> D = {x: x ** 2 for x in [1, 2, 3, 4]}
>>> D
{1: 1, 2: 4, 3: 9, 4: 16}

>>> D = {c: c * 4 for c in 'SPAM'}
>>> D
{'S': 'SSSS', 'P': 'PPPP', 'A': 'AAAA', 'M': 'MMMM'}
>>> D = {c.lower(): c + '!' for c in ['SPAM', 'EGGS',
'HAM']}
>>> D
{'eggs': 'EGGS!', 'spam': 'SPAM!', 'ham': 'HAM!'}

Initializing
Dictionaries
# Initialize dict from keys
>>> D = dict.fromkeys(['a', 'b',
'c'], 0)
>>> D
{'a': 0,'b': 0, 'c': 0}
# Same, but with a
comprehension
>>> D = {k:0 for k in ['a', 'b', 'c']}
>>> D

>>> D = {k: None for k in 'spam'}
>>> D {'s': None, 'p': None, 'a': None, 'm': None}
Dictionary methods
<dict>.items()
displays the items in the dictionary (pair of keys and
values)
<dict>.keys()
display the keys in the dictionary
<dict>.values()

<dict>.pop()
removes the last item from the dictionary
<dict2> = <dict1>.copy()
copies the items from dict1 to dict2
<dict>.clear()
removes all the items from the dictionary
str(dict)
produces printable string representation of a
dictionary
len(dict)
returns the number of items in the dictionary

Dictionaries can replace elif
ladder/switch-case
print ({1:’one’,2:’two’,3:’three’,4:’four’,5:’five’}
[choice]) if choice = 3 then the code prints
three

Exercise 1: Convert two lists into a dictionary.
Exercise 2: Merge two Python dictionaries into one.
Exercise 3: Create a dictionary by extracting the keys from a given
dictionary.
Exercise 4: Delete a list of keys from a dictionary.
Exercise 5: Check if a value exists in a dictionary.
Exercise 6: Rename key of a dictionary.
Exercise 7: Write a Python program to sum all the items in a dictionary.
Exercise 8: Write a Python program to sort a given dictionary by key.
Exercise 9: Write a Python program to get the maximum and minimum
value in a dictionary.

python advanced data structure dictionary with examples python advanced data structure dictionary with examples

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