IG Math Space

By the end of this class session, students will be able to:

• Describe the history and key features of the Python programming language.
• Understand identifiers, reserved keywords, variables and comments.
• Apply indentation rules and use multi-line / multiple-statement constructs.
• Use input(), print() and import functions effectively.
• Identify and apply all seven categories of Python operators.
• Understand operator precedence and associativity.

Python was developed by Guido van Rossum at the National Research Institute for Mathematics and Computer Science, Netherlands during 1985–1990. It is derived from languages such as ABC, Modula-3, C, C++, Algol-68, SmallTalk and Unix shell scripts.

The name Python was inspired by the BBC comedy series Monty Python's Flying Circus. Rossum wanted a short, unique and mysterious name.

Python is a general-purpose, interpreted, interactive, object-oriented and high-level programming language. Its source code is available under the GNU General Public License (GPL).

Identifiers

An identifier is a name used to identify a variable, function, class or module. Rules:

• Must begin with a letter (A–Z or a–z) or an underscore (_).
• Can be followed by letters, digits (0–9) or underscores.
• Case-sensitive: myVar and myvar are different identifiers.
• Special characters (@, #, $ etc.) are not allowed.
• Reserved keywords cannot be used as identifiers.

Reserved Keywords

The following words are reserved and cannot be used as identifiers:

Variables are reserved memory locations to store values. The interpreter allocates memory based on the data type and decides what can be stored.

Python variables do not need explicit declaration — memory is reserved automatically when a value is assigned using the = operator.

Assignment Examples

a    = 100        # Integer
b    = 1000.0     # Float
name = "John"     # String

print(a)          # 100
print(b)          # 1000.0
print(name)       # John

Multiple Assignment

a = b = c = 1              # Same value to multiple variables
a, b, c = 1, 2, "Tom"     # Different values to multiple variables

Comments describe what the code does and are for programmer readability. Python ignores comments during execution.

• Single-line comment — use the # symbol.
• Multi-line comment — use # on each line, or enclose in triple quotes (''' or """).

# This is a single-line comment

# This is a multi-line comment
# that spans several lines

"""
This is another
multi-line comment
using triple quotes
"""

Unlike C, C++ or Java which use braces {}, Python uses indentation to define blocks of code. A block starts with indentation and ends with the first un-indented line.

Four whitespaces are the recommended convention (preferred over a tab character).

if True:
    print("Correct")   # indented — inside the if block
else:
    print("Wrong")

Multi-Line Statements

Use the line continuation character \ or enclose in brackets to span a statement across lines:

total = 1 + 2 + \
        3 + 4

# Or using parentheses
total = (1 + 2 +
         3 + 4)

Multiple Statements on One Line

A group of individual statements making a code block is called a suite. Use a semicolon to write multiple statements on one line:

x = 10; y = 20; print(x + y)

Quotes in Python

Python accepts single ('), double (") and triple (''' / """) quotes to denote string literals. Triple quotes can span multiple lines.

s1 = 'Hello'
s2 = "World"
s3 = """This string
spans multiple
lines."""

print() — Displaying Output

The print() function converts expressions to strings and writes to standard output.

print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False)

sep — separator between values (default: space)  |  end — character after last value (default: newline)

print(1, 2, 3, 4)                   # 1 2 3 4
print(1, 2, 3, 4, sep='+')          # 1+2+3+4
print(1, 2, 3, 4, sep='+', end='%') # 1+2+3+4%

input() — Reading Input

Reads a line from the keyboard and always returns a string.

name = input("Enter your name: ")
print("Your name is:", name)

n = int(input("Enter a number: "))   # convert to int
print("The number is:", n)

import — Using Modules

When code grows large, it is organised into modules (.py files). Use the import keyword:

import math
print(math.pi)       # 3.141592653589793
print(math.sqrt(16)) # 4.0

An operator manipulates operands. In a = b + c, a, b, c are operands and =, + are operators. Python supports seven categories:

10.1 Arithmetic Operators

a, b, c = 10, 5, 2
print("Sum=",        a+b)   # 15
print("Difference=", a-b)   # 5
print("Product=",    a*b)   # 50
print("Quotient=",   a/b)   # 2.0
print("Remainder=",  b%c)   # 1
print("Exponent=",   b**c)  # 25
print("Floor Div=",  b//c)  # 2

10.2 Comparison (Relational) Operators

10.3 Assignment Operators

10.4 Logical Operators

a, b, c, d = 10, 5, 2, 1
print((a>b) and (c>d))   # True
print((a>b) or  (d>c))   # True
print(not(a>b))           # False

10.5 Bitwise Operators

10.6 Membership Operators

s = 'abcde'
print('a' in s)       # True
print('f' in s)       # False
print('f' not in s)   # True

10.7 Identity Operators

10.8 Operator Precedence (Highest → Lowest)

1. List any five features of Python with brief explanations.
2. Is Python a case-sensitive language? Give an example.
3. How can you run Python programs? Name at least two modes.
4. State the rules for naming an identifier in Python.
5. How are single-line and multi-line comments written in Python?
6. What is the difference between = (assignment) and == (comparison)?
7. Differentiate between is and == with an example.
8. What is the purpose of the import statement? Give an example.
9. Evaluate: 5 + 3 * 2 ** 2 // 4 - 1 — show step-by-step working.
10. Write a Python program to demonstrate all assignment operators.