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🔄 C# to Python Quick Reference Guide

A side-by-side comparison for CoderDojo students transitioning from C# to Python! 🐍💜

📝 Basic Syntax Comparison

Hello World 🌍

C# Python
Console.WriteLine("Hello!"); print("Hello!")

Comments 💬

C# Python
// Single line comment # Single line comment
/* Multi-line comment */ """ Multi-line comment """

Semicolons & Braces

C# Python
Required semicolons ; No semicolons needed!
Uses { } for code blocks Uses indentation (4 spaces)

📦 Variables

Declaring Variables

// C#
string name = "Alex";
int age = 14;
double height = 5.6;
bool isStudent = true;
# Python
name = "Alex"
age = 14
height = 5.6
is_student = True  # Note: True/False are capitalized!

Constants

// C#
const double PI = 3.14159;
# Python (by convention, use ALL_CAPS)
PI = 3.14159  # Not enforced, but everyone knows not to change it!

🔄 Data Types

C# Type Python Type Example
string str "Hello"
int int 42
double/float float 3.14
bool bool True / False
List<T> list [1, 2, 3]
Dictionary<K,V> dict {"key": "value"}
int[] (array) list [1, 2, 3]

🎤 Input/Output

Printing

// C#
Console.WriteLine("Hello!");
Console.WriteLine($"Name: {name}, Age: {age}");
Console.Write("No newline");
# Python
print("Hello!")
print(f"Name: {name}, Age: {age}")
print("No newline", end="")

Getting Input

// C#
Console.Write("Enter name: ");
string name = Console.ReadLine();

Console.Write("Enter age: ");
int age = int.Parse(Console.ReadLine());
# Python
name = input("Enter name: ")
age = int(input("Enter age: "))

🔀 Conditionals

If/Else Statements

// C#
if (age < 13)
{
    Console.WriteLine("Child");
}
else if (age < 20)
{
    Console.WriteLine("Teen");
}
else
{
    Console.WriteLine("Adult");
}
# Python
if age < 13:
    print("Child")
elif age < 20:
    print("Teen")
else:
    print("Adult")

Comparison Operators

C# Python Meaning
== == Equal to
!= != Not equal to
<, > <, > Less/Greater than
<=, >= <=, >= Less/Greater or equal
&& and Logical AND
|| or Logical OR
! not Logical NOT

🔄 Loops

For Loop (Counting)

// C#
for (int i = 0; i < 5; i++)
{
    Console.WriteLine(i);
}
# Python
for i in range(5):
    print(i)

For-Each Loop

// C#
string[] fruits = {"apple", "banana", "cherry"};
foreach (string fruit in fruits)
{
    Console.WriteLine(fruit);
}
# Python
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

While Loop

// C#
int count = 0;
while (count < 5)
{
    Console.WriteLine(count);
    count++;
}
# Python
count = 0
while count < 5:
    print(count)
    count += 1

📋 Lists/Arrays

Creating Lists

// C#
List<string> names = new List<string> { "Alice", "Bob", "Charlie" };
// or array:
string[] names = { "Alice", "Bob", "Charlie" };
# Python
names = ["Alice", "Bob", "Charlie"]

List Operations

Operation C# Python
Add item list.Add(item) list.append(item)
Remove item list.Remove(item) list.remove(item)
Get length list.Count len(list)
Access item list[0] list[0]
Last item list[list.Count - 1] list[-1]
Check if contains list.Contains(item) item in list
Clear list list.Clear() list.clear()

Python-Only: Slicing! 🔪

# Python
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

numbers[2:5]   # [2, 3, 4] - from index 2 to 4
numbers[:3]    # [0, 1, 2] - first 3 items
numbers[7:]    # [7, 8, 9] - from index 7 to end
numbers[-3:]   # [7, 8, 9] - last 3 items
numbers[::2]   # [0, 2, 4, 6, 8] - every 2nd item
numbers[::-1]  # [9, 8, 7, 6, 5, 4, 3, 2, 1, 0] - reversed!

📖 Dictionaries

Creating Dictionaries

// C#
var student = new Dictionary<string, object>
{
    { "name", "Alex" },
    { "age", 14 },
    { "grade", 8 }
};
# Python
student = {
    "name": "Alex",
    "age": 14,
    "grade": 8
}

Dictionary Operations

Operation C# Python
Get value dict["key"] dict["key"]
Set value dict["key"] = value dict["key"] = value
Check key exists dict.ContainsKey("key") "key" in dict
Get all keys dict.Keys dict.keys()
Get all values dict.Values dict.values()

🔧 Functions

Basic Function

// C#
void SayHello()
{
    Console.WriteLine("Hello!");
}
# Python
def say_hello():
    print("Hello!")

Function with Parameters

// C#
void Greet(string name)
{
    Console.WriteLine($"Hello, {name}!");
}
# Python
def greet(name):
    print(f"Hello, {name}!")

Function with Return Value

// C#
int Add(int a, int b)
{
    return a + b;
}
# Python
def add(a, b):
    return a + b

Default Parameters

// C#
void Greet(string name, string greeting = "Hello")
{
    Console.WriteLine($"{greeting}, {name}!");
}
# Python
def greet(name, greeting="Hello"):
    print(f"{greeting}, {name}!")

🏗️ Classes

Basic Class

// C#
class Dog
{
    public string Name { get; set; }
    public int Age { get; set; }

    public Dog(string name, int age)
    {
        Name = name;
        Age = age;
    }

    public void Bark()
    {
        Console.WriteLine($"{Name} says: Woof!");
    }
}

// Using it:
Dog buddy = new Dog("Buddy", 3);
buddy.Bark();
# Python
class Dog:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def bark(self):
        print(f"{self.name} says: Woof!")

# Using it:
buddy = Dog("Buddy", 3)
buddy.bark()

Key Differences in Classes

Feature C# Python
Constructor Same name as class __init__
Self reference this (optional) self (required)
Access modifiers public, private, etc. None (convention: _private)
Creating object new ClassName() ClassName()

🎯 Naming Conventions

What C# Style Python Style
Variables camelCase snake_case
Functions PascalCase snake_case
Classes PascalCase PascalCase
Constants PascalCase or UPPER_CASE UPPER_CASE
Private _name or private _name 
// C# Style
public class MyClass
{
    private string _firstName;
    public const int MaxValue = 100;

    public void DoSomething() { }
}
# Python Style
class MyClass:
    MAX_VALUE = 100

    def __init__(self):
        self._first_name = ""

    def do_something(self):
        pass

🧪 Common Operations

String Operations

Operation C# Python
Length str.Length len(str)
Upper case str.ToUpper() str.upper()
Lower case str.ToLower() str.lower()
Contains str.Contains("x") "x" in str
Split str.Split(' ') str.split(' ')
Join string.Join(", ", list) ", ".join(list)
Format $"Hello {name}" f"Hello {name}"

Math Operations

Operation C# Python
Power Math.Pow(2, 3) 2 ** 3 or pow(2, 3)
Square root Math.Sqrt(16) 16 ** 0.5 or math.sqrt(16)
Absolute Math.Abs(-5) abs(-5)
Round Math.Round(3.7) round(3.7)
Random new Random().Next(1, 10) random.randint(1, 10)

🎁 Python Extras (Things C# Doesn't Have!)

Multiple Assignment

# Python
a, b, c = 1, 2, 3
x, y = y, x  # Swap values!

List Comprehension

# Python
# Create a list of squares
squares = [x**2 for x in range(10)]
# Result: [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# Filter a list
evens = [x for x in range(20) if x % 2 == 0]
# Result: [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

Tuple Unpacking

# Python
def get_name_and_age():
    return "Alex", 14

name, age = get_name_and_age()

F-Strings with Expressions

# Python
x = 10
print(f"{x} squared is {x**2}")  # "10 squared is 100"

📊 Quick Reference Table

Concept C# Python
File extension .cs .py
Run code dotnet run python3 file.py
Comments // or /* */ # or """ """
True/False true/false True/False
Null/None null None
And/Or/Not &&/||/! and/or/not
String format $"text {var}" f"text {var}"
Main function static void Main() if __name__ == "__main__":

🎉 You Did It!

Now you know both C# and Python! 🐍💜

Remember:

  • C# is great for: Games (Unity), desktop apps, web APIs
  • Python is great for: AI, data science, automation, scripting

The best programmers know multiple languages! 🌟