Getting Started With Python

Python is a high-level, interpreted language designed to be easy to read and write. The interpreter translates Python code into bytecode and executes it, ultimately running machine-level instructions.

We use programming languages like Python because computers only understand binary (0s and 1s), programming languages provide a human-friendly way to write instructions that get translated into machine code.

We're using Python IDLE in this lecture as Python IDLE is a simple environment where you can run code interactively or save scripts as .py files and execute them from an editor or terminal.

Airthmetic Operations

Python supports the standard arithmetic operators. Below each operator is explained and illustrated with examples and expected output.

Addition +

>>> 2 + 3
5

Adds two numbers.

Subtraction -

>>> 9 - 8
1

Subtracts the right-hand operand from the left-hand operand.

Multiplication *

>>> 4 * 6
24

Multiplies operands.

True division / (returns float)

• The division operator / always returns a float even if both operands are integers.

>>> 8 / 4
2.0
>>> 5 / 2
2.5

This is useful because division can produce non-integer results; returning a float preserves precision.

Floor (integer) division //

• Use // if you want only the integer part (the quotient) and to discard any fractional remainder.

>>> 10 // 3
3
>>> -7 // 3
-3  # floor division rounds toward negative infinity

Note: with negative numbers // performs floor division — results may look unintuitive if you expect truncation toward zero.*

Modulus % (remainder)

>>> 10 % 3
1

Returns remainder of division.

Exponentiation **

>>> 2 ** 3
8
>>> 4 ** 0.5
2.0  # square root

Raises the left operand to the power of the right operand.

Operator precedence and parentheses

Python obeys the usual mathematical rules (BODMAS). Use parentheses to change order.

>>> 8 + 2 * 3
14
>>> (8 + 2) * 3
30

Common pitfall: incomplete expressions cause syntax errors:

>>> 8 + 9 -
SyntaxError: invalid syntax

Strings

A string is a sequence of characters. Strings can be enclosed in single quotes '...', double quotes "...", or triple quotes for multi-line strings '''...''' or """...""".

Single and double quotes

Both are equivalent, choose whichever avoids the need to escape characters.

>>> print('navin')
navin
>>> print("navin")
navin

Using quotes inside strings

• If the string contains an apostrophe, use double quotes outside to avoid escaping.

>>> print("navin's laptop")
navin's laptop

• If you must use the same quote inside and outside, escape the inner quote with a backslash \.

>>> print('navin\'s "laptop"')
navin's "laptop"

Triple-quoted strings (multi-line)

text = '''This is a
multi-line string.'''
print(text)

Escaping special characters

The backslash \ introduces escape sequences like \n (newline), \\ (a literal backslash), \t (tab), etc.

>>> print('Line1\nLine2')
Line1
Line2

Common error: mismatched quotes cause SyntaxError:

>>> print('navin's laptop')
SyntaxError: invalid syntax

Functions

A function is a block of organized, reusable code that performs a specific task. Python has many built-in functions (e.g., print(), len()) and you can define your own, which we will discuss in more detail later in the course.

Built-in function example

>>> len('hello')
5
>>> print('Hello, world!')
Hello, world!

Concatenation and Repetition of strings

Concatenation using +

Joins two strings into one. Both operands must be strings.

>>> 'navin' + ' reddy'
'navin reddy'

Repetition using *

Repeats a string multiple times.

>>> 'navin ' * 3
'navin navin navin '

Type error example:

>>> 'navin' + 5
TypeError: can only concatenate str (not "int") to str

6. New line character and raw strings

\n — newline character

\n in a string inserts a newline when printed.

>>> print('c:\\docs\navin')
c:\docs
avin

Raw strings r'...'

Raw strings treat backslashes \\ as literal characters. Useful for file paths or regular expressions.

>>> print(r'c:\docs\navin')
c:\docs\navin

Note: A raw string cannot end with a single backslash (r"something\" is invalid). Use normal strings or escape the final backslash.