Python fundamentals



Python Practice Notes

Python Practice Notes

Revision notes covering Python basics, loops, functions, and collection data types.

1. Indexing

Positive indexing starts at 0. Negative indexing starts at -1 from the end of a sequence.

classroom = [
    "sagar", "jathib", "jathias", "ranyad", "tata"
]

# Positive indexing: 0, 1, 2, 3, 4
# Negative indexing: -5, -4, -3, -2, -1

print(classroom[0])
print(classroom[-1])

print(type(classroom))
print(len(classroom[0]))

2. String Slicing and Step Functions

Syntax: string[start:stop:step]

name = "sasdas"

print(name[0:])    # From index 0 to the end
print(name[:2])    # From the beginning to index 1
print(name[::3])   # Every third character
print(name[::-2])  # Reverse with a step of 2

3. String Split Method

The split() method divides a string into a list using a specified separator.

name = "S A G A R"

print(type(name))

name = name.split(" ")

print(name)
print(type(name))

4. Escape Characters and User Input

Common escape characters:

  • \\ — Backslash
  • \n — New line
  • \" — Double quotation mark
a = input("Enter user name: ")
b = input("Enter another user name: ")

print(f"User has entered \\{a}\nand \"{b}\"")

5. Assignment Operators

a += b  # Equivalent to a = a + b
a -= b  # Equivalent to a = a - b
a *= b  # Equivalent to a = a * b

6. Loops

While Loop

A while loop repeats as long as its condition is true.

i = 0

while i <= 10:
    print(f"{i} is less than or equal to 10")
    i += 1

For Loop

A for loop iterates over a sequence or range of values.

# range(start, stop, step)

for i in range(1, 10):
    print(f"{i} is less than 10")

Break Statement

The break statement terminates a loop.

for i in range(1, 10):
    print(f"{i} is less than 10")

    if i == 5:
        break

Continue Statement

The continue statement skips the current iteration and moves to the next one.

for i in range(1, 10):
    if i == 5:
        continue

    print(f"{i} is less than 10")

Nested Loops

A nested loop is a loop inside another loop.

for i in range(1, 10):
    for j in range(10, 20):
        print(f"{i} * {j} = {i * j}")

7. Functions

Functions are reusable blocks of code defined using the def keyword.

def addition(a, b):
    for i in range(a, b):
        print(f"i value is {i} and b value is {b}")

addition(5, 7)

Return Values

def addition(a, b):
    return a + b

result = addition(1, 10)
print(result)

8. Lambda Functions

A lambda function is a small anonymous function.

multiply = lambda a, b: a * b
add = lambda x, y: x + y

print(add(3, 5))
print(multiply(3, 5))

9. Lists

Lists are ordered and mutable collections. They allow duplicate values and different data types.

l = [1, "asa", "sagar"]
z = [20, 30, 90, 10, 34, 67]

# Add an element at the end
l.append("python")

# Remove and return the last element
l.pop()

# Insert a value at a particular index
l.insert(1, "hello")

# Remove a particular value
l.remove("asa")

# Find the index of a value
print(l.index("sagar"))

# Sort a list
z.sort()

# Count occurrences of a value
print(z.count(10))

# Get the number of elements
print(len(z))

# Concatenate two lists
l1 = [20, 30, 40]
l2 = [60, 80, 90]
l3 = l1 + l2

print(l3)

List Comprehension

z = [i ** 2 for i in range(1, 10)]
print(z)

10. Tuples

Tuples are ordered and immutable collections. They allow duplicate values.

numbers = (10, 20, 30, 20)

print(numbers)
print(numbers[0])
print(len(numbers))

11. Sets

Sets store unique elements. They do not support indexing, and their iteration order should not be relied upon.

a = {1, 2, 3, 4, 5, 5, 5, 8}
print(a)

# Convert a list into a set
a = [10, 10, 10, 10, 20]
b = set(a)
c = list(b)

print(c)

Set Operations

a = {2, 4, 5, 7}
b = {7, 10, 2, 4}

# All unique elements from both sets
print(a.union(b))

# Common elements
print(a.intersection(b))

# Elements in a but not in b
print(a.difference(b))

# Elements in either set, but not both
print(a.symmetric_difference(b))

Set Comprehension

z = {i ** 2 for i in range(1, 10)}
print(z)

Frozenset

A frozenset is an immutable version of a set.

frozen = frozenset(z)
print(frozen)

12. Dictionaries

Dictionaries store data as key-value pairs. Keys must be unique and hashable.

a = {
    "name": "Death Note",
    "Episode": 1,
    "seen": 2
}

a["name"] = input("Enter anime name: ")

# Display key-value pairs
print(a.items())

# Display keys
print(a.keys())

# Display values
print(a.values())

# Access a value using its key
print(a["name"])

Dictionary Comprehension

z = {i: i ** 2 for i in range(1, 10)}
print(z)

13. Quick Revision

  • List: Ordered and mutable.
  • Tuple: Ordered and immutable.
  • Set: Unique elements, no indexing.
  • Frozenset: Immutable set.
  • Dictionary: Key-value pairs.
  • While loop: Repeats while a condition is true.
  • For loop: Iterates over a sequence or iterable.
  • Break: Exits the loop.
  • Continue: Skips to the next iteration.
  • Lambda: Creates a small anonymous function.

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