Lecture Notes Of Day 2 

Python Syntax and Variables

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Objective

• Understand Python’s syntax, including indentation.
• Learn about variables and their basic types in Python.

Outcome

By the end of this session, students will:

• Understand the rules of Python syntax and indentation.
• Be able to create and use variables of various types.

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1. Python Syntax

Python syntax refers to the set of rules that define the structure of a Python program. Unlike other programming languages, Python is designed to be highly readable.

Key Features of Python Syntax:

1.   Case Sensitivity

o    Python is case-sensitive. For example, myVar and myvar are treated as different variables.

2.   No Semicolons

o    Unlike languages like C or Java, Python does not require semicolons to terminate statements.

o    Example:

print("Hello, World!")  # No semicolon needed.

3.   Whitespace and Indentation

o    Python uses indentation (spaces or tabs) to define code blocks instead of curly braces {}.

o    A consistent level of indentation is mandatory.

o    Example:

if True:

    print("Indented block starts here.")

4.   Comments in Python

o    Single-line comments: Use the # symbol.
Example:

# This is a single-line comment.

print("Python comments start with #")

o    Multi-line comments: Use triple quotes (''' or """).
Example:

"""

This is a

multi-line comment.

"""

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2. Variables in Python

Variables are used to store data in Python. You can think of a variable as a container for storing values.

Rules for Defining Variables

1.   Variable names must start with a letter or an underscore (_).
Example: _myVariable, myVariable

2.   Variable names cannot start with a number.
Example: 2variable (invalid)

3.   Variable names can only contain alphanumeric characters and underscores (A-Z, a-z, 0-9, _).
Example: my_var, var123

4.   Variable names are case-sensitive.
Example: name and Name are different variables.

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Variable Declaration and Initialization

Variables in Python are created when you assign a value to them.
Example:

x = 10          # Integer

y = 3.14        # Float

name = "John"   # String

Dynamic Typing

• Python does not require you to declare the type of a variable explicitly.
• The type is inferred based on the value assigned.

Reassigning Variables

• Variables can be reassigned to a different type at any time.
• Example:

x = 10       # Initially an integer

x = "Hello"  # Now a string

print(x)     # Output: Hello

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3. Basic Variable Types

Python has several built-in types, including:

1.   Integer (int)

o    Represents whole numbers.

o    Example:

age = 25

print(age)  # Output: 25

2.   Float (float)

o    Represents numbers with decimal points.

o    Example:

price = 19.99

print(price)  # Output: 19.99

3.   String (str)

o    Represents a sequence of characters.

o    Strings are enclosed in either single or double quotes.

o    Example:

name = "Alice"

print(name)  # Output: Alice

4.   Boolean (bool)

o    Represents True or False.

o    Example:

is_python_fun = True

print(is_python_fun)  # Output: True

5.   None Type (None)

o    Represents the absence of a value.

o    Example:

x = None

print(x)  # Output: None

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4. Printing Variables

The print() function is used to output variables.

Example:

name = "Alice"

age = 25

height = 5.5

print("Name:", name)

print("Age:", age)

print("Height:", height)

Output:

Name: Alice 

Age: 25 

Height: 5.5 

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5. Type Checking and Conversion

1.   Checking the Type of a Variable

Use the type() function to check the type of a variable.
Example:

x = 10

print(type(x))  # Output: <class 'int'>

2.   Type Conversion

Python allows you to convert variables from one type to another.

o    Example:

x = 5      # Integer

y = str(x) # Convert to string

print(y)   # Output: "5"

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6. Best Practices for Using Variables

1.   Use meaningful variable names.

o    Instead of x, use age, name, etc.

2.   Avoid using Python reserved keywords as variable names (e.g., if, else, True).

3.   Keep variable names concise but descriptive.

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Exercise

1.   Create variables of different types:

o    Integer

o    Float

o    String

2.   Print their values and types using the print() and type() functions.

Example Solution:

# Creating variables

age = 20          # Integer

price = 15.75     # Float

name = "John Doe" # String

 

# Printing variables and their types

print("Age:", age, "Type:", type(age))

print("Price:", price, "Type:", type(price))

print("Name:", name, "Type:", type(name))

Expected Output:

Age: 20 Type: <class 'int'> 

Price: 15.75 Type: <class 'float'> 

Name: John Doe Type: <class 'str'> 

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Summary

• Python syntax emphasizes readability and uses indentation to define code blocks.
• Variables in Python are dynamically typed, meaning they do not require explicit declaration of data types.
• Python supports basic data types such as int, float, str, bool, and None.
• The print() function and type() function are essential for working with variables and understanding their types.

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