💡 Python Exam Cheatsheet

A quick review of core Python concepts frequently found in technical assessments and exams. This guide covers list comprehensions, dictionary methods, enumerate, and flexible function arguments.

# Create a list of squares for even numbers from 0 to 9
squares = [x**2 for x in range(10) if x % 2 == 0]
print(squares)

# Output:
# [0, 4, 16, 36, 64]

• List Comprehension: A concise, one-line syntax for creating lists.
• The structure is [expression for item in iterable if condition].
• The if condition part is optional and acts as a filter.

student_scores = {'Alice': 95, 'Bob': 87}

# Safely get a score, providing a default value if the key is missing
charlie_score = student_scores.get('Charlie', 'Not Found')
alice_score = student_scores.get('Alice', 'Not Found')

print(f"Alice: {alice_score}")
print(f"Charlie: {charlie_score}")

# Output:
# Alice: 95
# Charlie: Not Found

• Dictionary .get() Method: Safely access a dictionary key without causing a KeyError.
• The first argument is the key to look up.
• The optional second argument is the default value to return if the key does not exist.

colors = ['red', 'green', 'blue']

for index, value in enumerate(colors):
    print(f"Index: {index}, Value: {value}")

# Output:
# Index: 0, Value: red
# Index: 1, Value: green
# Index: 2, Value: blue

• Using enumerate: The Pythonic way to loop over an iterable when you need both the index and the value.
• It returns a tuple (index, value) for each item in the sequence.

def process_data(*args, **kwargs):
    print(f"Positional args (tuple): {args}")
    print(f"Keyword args (dict): {kwargs}")

process_data(1, 'hello', 3.14, user='admin', status='active')

# Output:
# Positional args (tuple): (1, 'hello', 3.14)
# Keyword args (dict): {'user': 'admin', 'status': 'active'}

• *args: Collects all extra positional arguments into a tuple.
• **kwargs: Collects all extra keyword arguments into a dictionary.
• This pattern allows a function to accept a variable number of arguments.

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By: @DataScience4 ✨

100 Python Examples: A Step-by-Step Guide

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Part 1: The Basics (Examples 1-15)

#1. Print "Hello, World!"
The classic first program. print() is a function that outputs text to the console.

print("Hello, World!")

Hello, World!

#2. Variables and Strings
Store text in a variable and print it.

message = "I am learning Python."
print(message)

I am learning Python.

#3. Integer Variable
Store a whole number.

age = 30
print("My age is:", age)

My age is: 30

#4. Float Variable
Store a number with a decimal point.

price = 19.99
print("The price is:", price)

The price is: 19.99

#5. Boolean Variable
Store a value that is either True or False.

is_learning = True
print("Am I learning?", is_learning)

Am I learning? True

#6. Get User Input
Use the input() function to get information from the user.

name = input("What is your name? ")
print("Hello, " + name)

What is your name? Alice
Hello, Alice

#7. Simple Calculation
Perform a basic arithmetic operation.

a = 10
b = 5
print(a + b)

15

#8. Comments
Use # to add comments that Python will ignore.

# This line calculates the area of a rectangle
length = 10
width = 5
area = length * width
print("Area is:", area)

Area is: 50

#9. Type Conversion (String to Integer)
Convert a user's input (which is a string) to an integer to perform math.

age_str = input("Enter your age: ")
age_int = int(age_str)
next_year_age = age_int + 1
print("Next year you will be:", next_year_age)

Enter your age: 25
Next year you will be: 26

#10. String Concatenation
Combine multiple strings using the + operator.

first_name = "John"
last_name = "Doe"
full_name = first_name + " " + last_name
print(full_name)

John Doe

#11. Multiple Assignment
Assign values to multiple variables in one line.

x, y, z = 10, 20, 30
print(x, y, z)

10 20 30

#12. The type() Function
Check the data type of a variable.

num = 123
text = "hello"
pi = 3.14
print(type(num))
print(type(text))
print(type(pi))

<class 'int'>
<class 'str'>
<class 'float'>

#13. Basic Arithmetic Operators
Demonstrates addition, subtraction, multiplication, and division.

a = 15
b = 4
print("Addition:", a + b)
print("Subtraction:", a - b)
print("Multiplication:", a * b)
print("Division:", a / b)

Addition: 19
Subtraction: 11
Multiplication: 60
Division: 3.75

#14. Floor Division and Modulus
// for division that rounds down, and % for the remainder.

a = 15
b = 4
print("Floor Division:", a // b)
print("Modulus (Remainder):", a % b)

Floor Division: 3
Modulus (Remainder): 3

#15. Exponentiation
Use ** to raise a number to a power.

power = 3 ** 4  # 3 to the power of 4
print(power)

81

---
Part 2: String Manipulation (Examples 16-25)

#16. String Length
Use len() to get the number of characters in a string.

my_string = "Python is fun"
print(len(my_string))

13

Python tip:
Use f-strings for easy and readable string formatting.

name = "Alice"
age = 30
message = f"Hello, my name is {name} and I am {age} years old."
print(message)

Python tip:
Utilize list comprehensions for concise and efficient list creation.

numbers = [1, 2, 3, 4, 5]
squares = [x * x for x in numbers if x % 2 == 0]
print(squares)

Python tip:
Use enumerate() to iterate over a sequence while also getting the index of each item.

fruits = ["apple", "banana", "cherry"]
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

Python tip:
Use zip() to iterate over multiple iterables in parallel.

names = ["Alice", "Bob"]
ages = [25, 30]
for name, age in zip(names, ages):
    print(f"{name} is {age} years old.")

Python tip:
Always use the with statement when working with files to ensure they are properly closed, even if errors occur.

with open("example.txt", "w") as f:
    f.write("Hello, world!\n")
    f.write("This is a test.")
# File is automatically closed here

Python tip:
Use *args to allow a function to accept a variable number of positional arguments.

def sum_all(*args):
    total = 0
    for num in args:
        total += num
    return total

print(sum_all(1, 2, 3))
print(sum_all(10, 20, 30, 40))

Python tip:
Use **kwargs to allow a function to accept a variable number of keyword arguments (as a dictionary).

def display_info(**kwargs):
    for key, value in kwargs.items():
        print(f"{key}: {value}")

display_info(name="Bob", age=40, city="New York")

Python tip:
Employ defaultdict from the collections module to simplify handling missing keys in dictionaries by providing a default factory.

from collections import defaultdict

data = [("fruit", "apple"), ("vegetable", "carrot"), ("fruit", "banana")]
categorized = defaultdict(list)
for category, item in data:
    categorized[category].append(item)
print(categorized)

Python tip:
Use if __name__ == "__main__": to define code that only runs when the script is executed directly, not when imported as a module.

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

if __name__ == "__main__":
    print("Running directly as a script.")
    print(greet("World"))
else:
    print("This module was imported.")

Python tip:
Apply type hints to your code for improved readability, maintainability, and to enable static analysis tools.

def add(a: int, b: int) -> int:
    return a + b

result: int = add(5, 3)
print(result)

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By: @DataScience4 ✨