Week 10.pptx

Why do we need Dictionary? (Why)
You can use a dictionary to look up the meaning of
any words that you don’t understand.
A good dictionary can help you understand your
subject better, improve your communication and
improve your grades by making sure you are using
words correctly.
2

Why do we need Dictionary in Python?
Dictionary in Python is an unordered collection of
data values, used to store data values like a map,
which, unlike other Data Types that hold only a single
value as an element, Dictionary holds key:value pair.
Key-value is provided in the dictionary to make it
more optimized.
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What is a Dictionary in Python?
A dictionary is a collection which is ordered (As of
Python version 3.7, dictionaries are ordered. In
Python 3.6 and earlier, dictionaries are unordered),
changeable and does not allow duplicates
Dictionaries are used to store data values in key:value
pairs.
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Creating a Dictionary in Python?
A Dictionary can be created by placing a sequence of
elements within curly {} braces, separated by
‘comma’.
Dictionary holds a pair of values, one being the Key
and the other corresponding pair element being
its Key:value.
Values in a dictionary can be of any data type and
can be duplicated, whereas keys can’t be repeated
and must be immutable.
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Creating a dictionary in Python?
Creating an empty dictionary:
Dict = {}
print("Empty Dictionary: ")
print(Dict)
Output: Empty Dictionary: {}
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Dict = {}
print(Dict)
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Dict = {}
print(Dict)
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Dict = {}
print(Dict)
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Nested dictionary?
Creg an empty dictionary:
Dict = {}
print(Dict)
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Create a nested dictionary in python?
Create a nested dictionary:
Dict = {1: 'Geeks', 2: 'For',
3:{'A' : 'Welcome', 'B' : 'To'}}
print(Dict)
Output: {{1: 'Geeks', 2: 'For', 3: {'A': 'Welcome',
'B': 'To'}}
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Accessing a dictionary element?
You can access the items of a dictionary by referring to its
key name, inside square brackets:
thisdict = {"brand": "Ford", "model": "Mustang", "year": 1964}
x = thisdict["model"]
Output: Mustang
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Accessing a dictionary element?
There is also a method called get() that will give you the same
result
thisdict = {"brand": "Ford", "model": "Mustang", "year": 1964}
x = thisdict.get("model“)
Output: Mustang
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Methods .keys and .values in
dictionary?
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Deleting a dictionary element?
del command can be used to del an element of
dictionary.
Example:
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How to check if a dictionary has a
p particular key?
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Operations on a dictionary?
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Extracting a value from dictionary?
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Add an item in a dictionary?
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Changing a value in a dictionary?
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Dictionary is a different from list?
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Iterating through a dictionary?
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Iterating through a dictionary?
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Keys of dictionary can be sorted using sort() function.

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Why do we need set in Python?
Set is one of 4 built-in data types in Python used to
store collections of data, the other 3
are List, Tuple, and Dictionary, all with different
qualities and usage.
36

What is a set in Python?
A set is a collection which is unordered,
unchangeable, and unindexed.
Set don’t allow duplicate values.
Set items can be of any data type.
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How set is different from dictionary?
For a dictionary, hash tables store three elements:
hash, key, and value.
For a set, the difference is that there is no key-
value pairing in the hash table, only a single
element.
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Creating a set in Python?
Sets are written in curly brackets {}.
Example:
thisset = {"apple", "banana", "cherry"}
print(thisset)
Output: {‘apple’, ‘banana’, ‘cherry’}
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Creating a set in Python?
It is also possible to use the set() constructor to
make a set.
Example:
thisset = set(("apple", "banana", "cherry"))
print(thisset)
Output: {‘apple’, ‘banana’, ‘cherry’}
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Accessing item from a set?
You cannot access items in a set by referring to an
index or a key. But you can loop through the set items
using a for loop, or ask if a specified value is present in
a set, by using the in keyword.
Example:
for x in thisset:
print(x)
Output: apple
banana
cherry
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Accessing item from a set?
Use in keyword to check if specific element is present in
the set or not.
Example:
print("banana" in thisset)
Output: True
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How to update a set?
Once a set is created, you cannot change its items, but
you can add new items
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How to add an item in a set?
To add one item to a set use the add() method.
Example:
thisset.add("orange")
print(thisset)
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Output: {"apple", “banana", “orange“,”cherry”}

How to add an item in a set?
To add items from another set into the current set, use
the update() method.
Example:
tropical = {"pineapple", "mango", "papaya"}
thisset.update(tropical)
print(thisset)
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Output: {'apple', 'mango', 'cherry', 'pineapple',
'banana', 'papaya'}

How to remove an item in a set?
To remove an item in a set, use the remove(), or
the discard() method.
If the item to remove does not exist, remove() will raise
an error
Example:
thisset.remove("banana")
print(thisset)
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Output: {‘apple’, ’cherry’}

To remove an item in a set by using the discard() method.
If the item to remove does not exist, discard() will not
raise an error.
Example:
thisset.discard("banana")
print(thisset)
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Output: {‘apple’, ’cherry’}

You can also use the pop() method to remove an item, but
this method will remove the last item.
Remember that sets are unordered, so you will not know
what item that gets removed.
Example:
x = thisset.pop()
print(x)
print(thisset)
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Output: apple
Output: {‘cherry’, ’banana’}

How to join two sets?
You can use the union() method that returns a new set
containing all items from both sets
Example:
set1 = {"a", "b" , "c"}
set2 = {1, 2, 3}
set3 = set1.union(set2)
print(set3)
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Output: {'b', 3, 'c', 'a', 1, 2}

The update() method that inserts all the items from one
set into another.
Both union() and update() will exclude any duplicate
items.
Example:
set1 = {"a", "b" , "c"}
set2 = {1, 2, 3}
set1.update(set2)
print(set1)
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Output: {'b', 2, 'c', 'a', 1, 3}

The intersection_update() method will keep only the items
that are present in both sets.
Example:
x = {"apple", "banana", "cherry"}
y = {"google", "microsoft", "apple"}
x.intersection_update(y)
print(x)
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Output: {‘apple'}

Set methods?
Python has built-in methods that you can use on t
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Set methods?
Python has built-in methods that you can use on t
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Learning Objective
In this lecture, we learnt what is a
dictionary and set, why we need
dictionary and set, how to create and
write a dictionary and list in Python
and which operations we can perform
on dictionary and list.
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Conclusion
● To store multiple data in programming, list is
used.
● With the help of dictionary and set methods
we can perform many operations on dictionary
and set.
● Built-In functins can also be used on
dictionary and set.
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Self Assessment
Solve the Following Programs
1. Write a program to use the get method to print the
value of the "model" key of the car dictionary.
car = { "brand": "Ford", "model": "Mustang", "year":
1964 }
2. Write a program to change the “year” value from
1964 to 2021.
3. Write a program to add key/value pair “color”:red in
a car dictionary.
4. Write a program to use the pop method to remove
"model" from the car dictionary
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Self Assessment
Solve Following Programs
1. Write a Program that takes two dictionaries and
returns true if they have at least one common
element.
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Self Assessment
Solve Following Programs
1. Write a program to check if “apple” is present in
fruits set or not.
fruits = {“apple”,”banana”,”cherry”}
2. Write a program to add “orange” to the fruits set
given above.
3. Write a program to remove “banana” from a fruits
set.
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