Dictionary and Sets
Dictionary and Sets
Dictionary is a collection of key-value pairs.
Syntax:
''' a = {“key”: “value”,
“alok”: “code”,
“marks” : “100”,
“list”: [1,2,9]}
a[“key”] #
Prints value
a[“list”] #
Prints [1,2,9] '''
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Properties of Python Dictionaries
1.
It is unordered
2.
It is mutable
3.
It is indexed
4.
It cannot contain duplicate keys
Dictionary Methods
Consider the following dictionary,
a = {“name”: “alok”,
“from”: “India”,
“marks”:
[92,98,96]}
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1.
items() : returns a list of
(key,value) tuple.
2.
keys() : returns a list containing
dictionary’s keys.
3.
update({“friend”: “Sam”}) : updates
the dictionary with supplied key-value pairs.
4.
get(“name”) : returns
the value of the specified keys (and value is returned e.g., “Alok” is returned
here)
More methods are available on docs.python.org
Sets in Python
Set is a collection of non-repetitive elements.
S=
Set() # No repetition allowed!
S.add(1)
S.add(2)
# or Set = {1,2}
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If you are a programming beginner without much knowledge of
mathematical operations on sets, you can simply look at sets in python as data
types containing unique values.
Properties of Sets
1.
Sets are unordered # Elements order doesn’t matter
2.
Sets are unindexed # Cannot access elements by index
3.
There is no way to change items in sets
4.
Sets cannot contain duplicate values
Operations on Sets
Consider the following set:
S = {1,8,2,3}
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1.
Len(s) : Returns 4, the length of
the set
2.
remove(8) : Updates
the set S and removes 8 from S
3.
pop() : Removes an arbitrary
element from the set and returns the element removed.
4.
clear() : Empties
the set S
5.
union({8, 11}) : Returns a
new set with all items from both sets. #{1,8,2,3,11}
6.
intersection({8, 11}) : Returns a
set which contains only items in both sets. #{8}
Chapter 5 – Practice Set
1.
Write a program to create a dictionary of Hindi words with values
as their English translation. Provide the user with an option to look it up!
2.
Write a program to input eight numbers from the user and display
all the unique numbers (once).
3.
Can we have a set with 18(int) and “18”(str) as a value in it?
4.
What will be the length of the following set S:
S = Set()
S.add(20)
S.add(20.0)
S.add(“20”)
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What will be the length of S after the above operations?
5.
S = {}, what is the type of S?
6.
Create an empty dictionary. Allow 4 friends to enter their
favorite language as values and use keys as their names. Assume that the names
are unique.
7.
If the names of 2 friends are the same; what will happen to the
program in Program 6?
8.
If the languages of two friends are the same; what will happen to
the program in Program 6?
9.
Can you change the values inside a list which is contained in set
S
S = {8, 7, 12, “alok”, [1, 2]}