Python Programming

Python is an interpreted, high-level, dynamic language.

Variables and Data Types

Python supports various data types including integers, floats, strings, and booleans.

Boolean

y = True
z = False

Numericals

# Integer
x = 5

# Float
y = 3.14

# Complex
z = 3 + 4j # j is used instead of i

String

name = "Alice"

Strings can be sliced.

text = "Hello World"

# Basic slicing: text[start:end]
print(text[0:5])    # "Hello" (index 0 to 4)
print(text[6:])     # "World" (index 6 to end)
print(text[:5])     # "Hello" (start to index 4)

# Using step: text[start:end:step]
print(text[::2])    # "HloWrd" (every 2nd character)
print(text[::-1])   # "dlroW olleH" (reverse string)

Operator precedence

Operator	Description
**	Exponentiation
~, +, -	Complement, unary plus, and minus
*, /, %, //	Multiply; divide, modulo, floor division
+, -	Addition and subtraction
>>, <<	Right and left bitwise shift
&	Bitwise AND
^, |	Bitwise XOR and OR
<=, <, >, >=	Comparison operators
==, !=	Equality operators
=, %=, /=, //=, -=, +=, *=, **=	Assignment operators
is, is not	Identity operators
in, not in	Membership operators
not, or, and	Logical operators

Control Structures

Python uses indentation to define blocks of code.

Selection

if x > 0:
    print("x is positive")
elif x < -2:
    print("x is lesser than -2")
else:
    print("x is between -2 and 0 (inclusive)")

elif and else sections are optional.

match-case syntax can be used for pattern matching.

point = (0, 0)
match point:
  case (0, 0):
    print("Origin")
  case (0, y):
    print(f"Y axis at {y}")
  case (x, 0):
    print(f"X axis at {x}")
  case (x, y):
    print(f"Point at {x}, {y}")

Repetition

Executing a block of code multiple times.

# For loop
for i in range(5):
  print(i) # i ranges from 0 (inclusive) to 5 (exclusive)

In for loop, the looping variable is automatically incremented.

# While loop
count = 0
while count < 5:
  print(count)
  count += 1

Subprogram (functions)

A reusable block of code that is used to perform a single action. Defined using the def keyword, followed by its name and ().

def greet(name):
    return f"Hello, {name}!"

print(greet("Alice"))

Lists

Lists are ordered collections of items. The items can be of any type. Items are indexed sequentially starting from 0.

fruits = ["apple", "banana", "cherry"]
print(fruits[0])  # Output: apple

# Adding an item to the list
fruits.append("date")

# Removing an item from the list
fruits.remove("banana")

# Accessing the last item
print(fruits[-1])  # Output: date

# Slicing the list
print(fruits[1:3])  # Output: ['cherry', 'date']

# Printing all the elements
## 1st way
for index in range(len(fruits)):
  print(fruits[index]) # index is a number between 0 and len(fruits)
## 2nd way
for fruit in fruits:
  print(fruit) # fruit is an item of the list

Tuples

Similar to lists but immutable (cannot be changed after creation). () are used instead of [].

# Creating a tuple
coordinates = (4, 5)
print(coordinates[0])  # Output: 4

# Tuple with different data types
mixed_tuple = (1, "hello", True)

# Cannot modify tuple
# This will raise an error:
# coordinates[0] = 10

# Creating tuple with one element
single_tuple = (1,)  # Note the comma

# Multiple assignment using tuple
x, y = coordinates
print(x)  # Output: 4
print(y)  # Output: 5

Commonly used for returning multiple values from functions or when you want to ensure data cannot be modified.

Dictionary

Stores key-value pairs.

student = {
    "name": "Alice",
    "age": 21,
    "is_student": True
}

print(student["name"])  # Output: Alice

# Adding a new key-value pair
student["major"] = "Computer Science"

# Updating an existing value
student["age"] = 22

# Removing a key-value pair
del student["is_student"]

# Accessing all keys
print(student.keys())  # Output: dict_keys(['name', 'age', 'major'])

# Accessing all values
print(student.values())  # Output: dict_values(['Alice', 22, 'Computer Science'])

There are a handful of built-in functions in Python.

Error Handling

Python uses try-except blocks for error handling.

try:
  # Code that might raise an exception
  x = 1 / 0
except ZeroDivisionError:
  print("Cannot divide by zero!")
except Exception as e:
  print(f"An error occurred: {e}")
else:
  # Runs if no exception occurs
  print("Operation successful")
finally:
  # Always runs
  print("Cleanup code")

Common exceptions:

• ValueError: Invalid value
• TypeError: Invalid operation on types
• FileNotFoundError: File doesn’t exist
• IndexError: List index out of range
• KeyError: Dictionary key not found

Exceptions can be raised when required.

def divide(a, b):
  if b == 0:
    raise ValueError("Division by zero!")
  return a / b