Lecture
Notes Of Day 2 Python Syntax and Variables
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.
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.
"""
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.
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
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
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
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"
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.
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'>
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.
