Smart Data and Discovery: Data Types

Data Types in Python

Overview

This lecture covers fundamental data types in Python: Lists, Tuples, Sets, and Dictionaries.

Lists

  • Ordered, mutable collections of elements accessed by index.

  • Can be heterogeneous or homogeneous.

  • Support slicing.

Creating Lists

  • Without constructor: Num = [], Num = [7, 8, 9], Num = [1, "Hello", 3.4], Num = ["Welcome", [4, 5, 6]]

  • With constructor: Num = list(), Num = list([7, 8, 9])

Accessing Items

  • Use [] with indexing starting from 0.

  • Example: num = [1, 2, 3, 4, 5]

    • print(num[1]) # Output: 2

    • print(num[-1]) # Output: 5

Slicing Lists

  • Access a range of items using [:].

  • Example: A = [1, 2, 3, 4, 5]

    • print(A[0:4]) # Output: [1, 2, 3, 4]

    • print(A[-2:-1]) # Output: [4]

List Methods

  • append(), extend(), insert(), remove(), pop(), clear(), index(), count(), sort(), reverse(), copy()

Examples of List Methods

  • Appending and Extending: Num = [1, 3, 4, 5]

    • Num.append(7) # Output: [1, 3, 4, 5, 7]

    • Num.extend([8, 9]) # Output: [1, 3, 4, 5, 7, 8, 9]

  • Other Operations: Num = [5, 4, 2, 1, 3]

    • Num.index(4) # Returns 1

    • Num.sort() # Output: [1, 2, 3, 4, 5]

    • Num.reverse() # Output: [5, 4, 3, 2, 1]

Tuples

  • Immutable sequences enclosed in ().

  • Faster iteration than lists.

Creating Tuples

  • Example: t = (1, 2, 3, 4), t1 = ('a', 'b', 'c')

Immutability

  • Tuples do not support item assignment or append() method.

Sets

  • Unordered collections of unique items.

  • Mutable.

Set Operations

  • Union, Intersection, Difference, Symmetric Difference

Set Methods

  • add(), remove()

Examples
a = {'dog', 'cat', 'mouse', 'parrot'}
b = {'cat', 'mouse', 'elephant', 'lion'}

a.union(b)            # Output: {'cat', 'dog', 'elephant', 'lion', 'mouse', 'parrot'}
a.intersection(b)   # Output: {'cat', 'mouse'}
a.difference(b)       # Output: {'dog', 'parrot'}
b.difference(a)       # Output: {'elephant', 'lion'}
a.symmetric_difference(b) # Output: {'dog', 'elephant', 'lion', 'parrot'}
s = set("hello")         # Output: {'e', 'h', 'l', 'o'}
s.add("i")             # Output: {'e', 'h', 'i', 'l', 'o'}
s.remove("e")          # Output: {'h', 'i', 'l', 'o'}
Dictionaries

  • Unordered collections of key-value pairs.

  • Mutable.

  • Keys must be unique and immutable.

Why Use Dictionaries?

  • Efficient data retrieval using keys.

  • Faster than lists for searching.

  • Allow association of values to unique keys.

Dictionary Methods

  • clear(), copy(), fromkeys(), get(), items(), keys(), pop(), values()

Examples
d = {"a": 1, "b": 2, "c": 3}
print(d)        # Output: {'a': 1, 'b': 2, 'c': 3}
print(d["a"])   # Output: 1
d["d"] = 4      # Adds a new key-value pair
print(d)        # Output: {'a': 1, 'b': 2, 'c': 3, 'd': 4}
d["a"] = 11     # Updates the value for the existing key
print(d)        # Output: {'a': 11, 'b': 2, 'c': 3, 'd': 4}
del d['d']
print(d) # Output: {'a': 11, 'b': 2, 'c': 3}
for key, value in d.items():
    print(key, value)

Squares = {1: 4, 5: 9, 6: 8, 5: 5}  # Note that duplicate keys are overwritten
print(Squares)  # Output: {1: 4, 5: 5, 6: 8}
print(len(Squares)) # Output: 3
print(sorted(Squares)) # Output: [1, 5, 6]