Some simple code examples for Python

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Python is a versatile and beginner-friendly language! Here are some simple code examples covering fundamental concepts.

1. Hello, World! (Basic Output)

The classic first program.

# This is a comment. Comments are ignored by the Python interpreter.

print("Hello, World!")
print("Python is fun!")

Explanation:

  • print() is a built-in function that displays output to the console.
  • Text inside double quotes ("") is called a string.

2. Variables and Data Types

Variables are used to store data. Python automatically determines the data type.

# Integers (whole numbers)
age = 30
score = 150

# Floating-point numbers (numbers with decimal points)
price = 19.99
pi = 3.14159

# Strings (sequences of characters)
name = "Alice"
city = 'New York' # Single quotes also work for strings

# Booleans (True or False values)
is_student = True
has_license = False

# Printing variables
print("Name:", name)
print("Age:", age)
print("Price:", price)
print("Is student:", is_student)

# You can also change a variable's value
age = 31
print("New Age:", age)

Explanation:

  • You assign a value to a variable using the = operator.
  • Python supports different data types like int, float, str, and bool.
  • You can print multiple items by separating them with commas in the print() function.

3. User Input

Get information directly from the user.

# Get a string input
user_name = input("Enter your name: ")
print("Hello,", user_name + "!")

# Get a number input (input() always returns a string, so convert it)
fav_number_str = input("What's your favorite number? ")
fav_number = int(fav_number_str) # Convert the string to an integer

print("Your favorite number is:", fav_number)
print("Your favorite number doubled is:", fav_number * 2)

Explanation:

  • input() displays a prompt to the user and waits for them to type something and press Enter. It always returns the input as a string.
  • int() is used to convert a string to an integer. You can also use float() for decimal numbers.

4. Conditional Statements (if, elif, else)

Execute different code blocks based on conditions.

age = 17

if age >= 18:
    print("You are an adult.")
    print("You can vote.")
elif age >= 13: # This condition is checked if the first 'if' is False
    print("You are a teenager.")
else: # This block runs if all previous conditions are False
    print("You are a child.")

# Another example
temperature = 25

if temperature > 30:
    print("It's hot outside!")
elif temperature < 10:
    print("It's cold outside!")
else:
    print("The weather is moderate.")

Explanation:

  • if, elif (else if), and else define blocks of code.
  • Indentation is crucial in Python! Code blocks are defined by indentation (typically 4 spaces).
  • Conditions use comparison operators: > (greater than), < (less than), >= (greater than or equal to), <= (less than or equal to), == (equal to), != (not equal to).

5. Loops (for loop and while loop)

Repeat a block of code multiple times.

a) For Loop (Iterating over a sequence)

# Iterate over a list of items
fruits = ["apple", "banana", "cherry"]
print("My favorite fruits:")
for fruit in fruits:
    print(fruit)

# Iterate a specific number of times using range()
print("\nCounting from 0 to 4:")
for i in range(5): # range(5) generates numbers 0, 1, 2, 3, 4
    print(i)

print("\nCounting from 1 to 5:")
for i in range(1, 6): # range(start, end+1)
    print(i)

Explanation:

  • The for loop is excellent for iterating over collections (like lists) or a sequence of numbers generated by range().

b) While Loop (Repeating as long as a condition is true)

count = 0
print("Counting up to 3:")
while count < 3:
    print(count)
    count = count + 1 # Increment the count, otherwise it's an infinite loop!

print("Loop finished.")

# A simple guessing game
secret_number = 7
guess = 0

while guess != secret_number:
    guess_str = input("Guess the secret number (1-10): ")
    guess = int(guess_str)

    if guess < secret_number:
        print("Too low! Try again.")
    elif guess > secret_number:
        print("Too high! Try again.")

print("Congratulations! You guessed it:", secret_number)

Explanation:

  • The while loop continues to execute its block of code as long as its condition remains True.
  • It's important to ensure that the condition eventually becomes False to avoid an infinite loop.

6. Functions

Group related code into reusable blocks.

# Define a simple function with no parameters
def say_hello():
    print("Hello there!")
    print("Welcome to Python functions.")

# Call the function
say_hello()
say_hello() # You can call it multiple times

# Define a function with parameters
def greet(name):
    print(f"Hi, {name}!") # f-string for easy string formatting

# Call the function with an argument
greet("Alice")
greet("Bob")

# Define a function that returns a value
def add_numbers(a, b):
    sum_result = a + b
    return sum_result # The function sends back this value

# Use the returned value
result = add_numbers(5, 3)
print("The sum is:", result)

another_sum = add_numbers(10, 20)
print("Another sum is:", another_sum)

Explanation:

  • def is used to define a function.
  • Parameters are variables listed inside the parentheses in the function definition (e.g., name, a, b).
  • Arguments are the actual values passed to the function when it's called.
  • return sends a value back from the function. If a function doesn't have a return statement, it implicitly returns None.

7. Lists (Ordered, Changeable Collections)

Store multiple items in a single variable.

# Creating a list
my_list = [1, 2, 3, "apple", True]
print("My list:", my_list)

# Accessing elements by index (lists are 0-indexed)
print("First element:", my_list[0]) # Output: 1
print("Fourth element:", my_list[3]) # Output: apple

# Changing an element
my_list[1] = "banana"
print("List after change:", my_list)

# Adding elements
my_list.append("orange") # Adds to the end
print("List after append:", my_list)

# Length of the list
print("Length of list:", len(my_list))

# Slicing a list (getting a sub-list)
print("Slice from index 1 to 3 (exclusive):", my_list[1:4])

Explanation:

  • Lists are defined using square brackets [].
  • Elements are ordered, meaning they have an index (position).
  • Lists are "mutable," meaning you can change, add, or remove elements after creation.

8. Dictionaries (Key-Value Pairs)

Store data in key-value pairs, like a real-world dictionary.

# Creating a dictionary
person = {
    "name": "Charlie",
    "age": 28,
    "city": "London",
    "is_student": False
}
print("Person dictionary:", person)

# Accessing values by key
print("Name:", person["name"])
print("Age:", person["age"])

# Adding a new key-value pair
person["occupation"] = "Engineer"
print("After adding occupation:", person)

# Modifying a value
person["age"] = 29
print("After changing age:", person)

# Getting all keys or values
print("All keys:", person.keys())
print("All values:", person.values())

# Iterating through a dictionary
print("\nPerson details:")
for key, value in person.items():
    print(f"{key}: {value}")

Explanation:

  1. Dictionaries are defined using curly braces {} with key-value pairs separated by colons.
  2. Keys must be unique and immutable (like strings, numbers, tuples). Values can be anything.
  3. Access values using dictionary_name[key].

How to Run This Code

  • Save: Copy and paste the code into a text editor (like Notepad, VS Code, Sublime Text, Atom) and save it with a .py extension (e.g., my_examples.py).
  • Open Terminal/Command Prompt: Navigate to the directory where you saved the file.
  • Run: Type python my_examples.py and press Enter.

These examples should give you a solid foundation for understanding basic Python programming!

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