Python Sequence Data Types - Complete Guide

Python Sequence Data Types | Lists, Tuples, and Dictionary

1. Sequence Data Types

A sequence is an ordered collection of items where each item is stored at a specific position called an index. Python supports the following sequence types:

  • Lists
  • Tuples
  • Dictionaries (although technically not a sequence, they are often grouped due to their key-value structure)

2. Lists

Definition: A list is an ordered, mutable collection of items. Lists are written using square brackets [ ], and items are separated by commas.

Characteristics of Lists:

  • Ordered: Items maintain a specific order.
  • Mutable: Items can be changed, added, or removed.
  • Duplicates allowed: Lists can contain duplicate items.
  • Heterogeneous: Lists can store multiple data types.
# Example: List in Python
fruits = ['apple', 'banana', 'cherry', 'apple']
print(fruits[0])  # Output: apple
fruits[1] = 'blueberry'
print(fruits)  # Output: ['apple', 'blueberry', 'cherry', 'apple']
fruits.append('mango')
print(fruits)  # Output: ['apple', 'blueberry', 'cherry', 'apple', 'mango']

3. Tuples

Definition: A tuple is an ordered, immutable collection of items. Tuples are written using parentheses ( ), and items are separated by commas.

Characteristics of Tuples:

  • Ordered: Items maintain a specific order.
  • Immutable: Items cannot be changed after creation.
  • Duplicates allowed: Tuples can contain duplicate items.
  • Heterogeneous: Tuples can store multiple data types.
# Example: Tuple in Python
numbers = (1, 2, 3, 4, 5)
print(numbers[1])  # Output: 2
# numbers[1] = 10  # TypeError: 'tuple' object does not support item assignment
a, b, c, d, e = numbers
print(a, b)  # Output: 1 2

4. Dictionaries

Definition: A dictionary is an unordered collection of key-value pairs. Dictionaries are written using curly braces { }, and key-value pairs are separated by a colon :.

Characteristics of Dictionaries:

  • Key-Value Pairs: Keys are unique, and values are associated with these keys.
  • Mutable: Key-value pairs can be added, modified, or removed.
  • Unordered: Keys do not maintain a specific order.
# Example: Dictionary in Python
student = {'name': 'John', 'age': 25, 'course': 'Python'}
print(student['name'])  # Output: John
student['age'] = 26
print(student)  # Output: {'name': 'John', 'age': 26, 'course': 'Python'}
student['grade'] = 'A'
print(student)  # Output: {'name': 'John', 'age': 26, 'course': 'Python', 'grade': 'A'}

5. Slicing

Definition: Slicing is used to extract a subset of elements from a sequence using the syntax:

sequence[start:stop:step]

Example:

numbers = [0, 1, 2, 3, 4, 5]
print(numbers[1:4])  # Output: [1, 2, 3]
print(numbers[:3])   # Output: [0, 1, 2]
print(numbers[::2])  # Output: [0, 2, 4]

6. Indexing

Definition: Indexing is used to access individual elements in a sequence. Indexing starts at 0.

fruits = ['apple', 'banana', 'cherry']
print(fruits[0])  # Output: apple
print(fruits[-1]) # Output: cherry (last element)

7. Concatenation

Definition: Concatenation combines two or more sequences using the + operator.

list1 = [1, 2, 3]
list2 = [4, 5, 6]
combined = list1 + list2
print(combined)  # Output: [1, 2, 3, 4, 5, 6]

8. Other Operations on Sequence Data Types

  • len(): Returns the length of the sequence.
  • max(): Returns the maximum value.
  • min(): Returns the minimum value.
  • in: Checks if an element exists in the sequence.
numbers = [10, 20, 30, 40]
print(len(numbers))  # Output: 4
print(max(numbers))  # Output: 40
print(min(numbers))  # Output: 10
print(20 in numbers) # Output: True
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