Python - Variable and data types

Variables in Python

  • A variable in Python is a named location used to store data in memory.
  • It's a fundamental concept that allows developers to store, modify, and retrieve data.
  • Unlike some programming languages, Python does not require explicit declaration of variable types, making it dynamically typed.
Creating Variables

To create a variable in Python, you simply assign a value to a variable name using the equals sign (=). For example:

x = 5
name = "Alice"
pi = 3.14
is_valid = True

In the examples above:

  • x is an integer variable.
  • name is a string variable.
  • pi is a floating-point variable.
  • is_valid is a boolean variable.
Naming Conventions

Variable names in Python should follow certain rules:

  • They must start with a letter or an underscore (_).
  • They can be followed by letters, numbers, or underscores.
  • They are case-sensitive (Age, age, and AGE are different variables).

It's also good practice to use descriptive names for variables to make the code more readable. For example, student_name is more informative than sn.

Data Types in Python

Data types specify the type of data that a variable can hold. Python provides several built-in data types, and it also allows for custom data types. Let's explore some of the primary built-in data types.

Numeric Types
  1. Integers (int): Integers are whole numbers, positive or negative, without decimals. Examples include -10, 0, and 42.

    age = 30
    2. Floating-Point Numbers (float): Floating-point numbers are numbers with decimal points. Examples include 3.14, -0.001, and 2.0.
    temperature = 98.6
    3. Complex Numbers (complex): Complex numbers have a real part and an imaginary part, denoted by j in Python.

    z = 2 + 3j
Sequence Types
  1. Strings (str): Strings are sequences of characters enclosed in single, double, or triple quotes.

    message = "Hello, World!"
  2. Lists (list): Lists are ordered collections of items, which can be of different data types. They are mutable, meaning they can be changed after creation.

    fruits = ["apple", "banana", "cherry"]
  3. Tuples (tuple): Tuples are similar to lists but are immutable, meaning they cannot be changed after creation.

    coordinates = (10, 20)
Mapping Type
  • Dictionaries (dict): Dictionaries are unordered collections of key-value pairs. They are mutable and indexed by keys.

    student = {"name": "Alice", "age": 23, "grade": "A"}
Set Types
  1. Sets (set): Sets are unordered collections of unique items. They are mutable.

    unique_numbers = {1, 2, 3, 4}
  2. Frozen Sets (frozenset): Frozen sets are immutable sets.

    immutable_set = frozenset([1, 2, 3, 4])
Boolean Type
  • Booleans (bool): Booleans represent one of two values: True or False.

    is_active = True
None Type
  • NoneType: This type has a single value, None, used to represent the absence of a value.

    result = None

Type Conversion

Python allows for type conversion, also known as typecasting. This is useful when you need to convert a value from one data type to another. Here are some common type conversions:

``python x = 5 # int y = float(x) # convert int to float z = str(x) # convert int to string a = "123" b = int(a) # convert string to int