Python Crash Course I

# Comments start with #
print("Hello, World!")  # Output to console

# Variables - no declaration needed
name = "Data Analyst"
age = 25
salary = 75000.50
is_employed = True

# Integer
count = 100

# Float
price = 99.99

# Operations
total = count * price
average = total / count

# Creating strings
message = "Hello"
name = 'Python'

# String operations
full_message = message + " " + name
repeated = message * 3

# String methods
upper_case = message.upper()
length = len(message)

# Creating lists
numbers = [1, 2, 3, 4, 5]
mixed = [1, "two", 3.0, True]

# Accessing elements
first = numbers[0]
last = numbers[-1]

# List methods
numbers.append(6)
numbers.remove(3)
length = len(numbers)

# Creating dictionaries
person = {
    "name": "John",
    "age": 30,
    "city": "New York"
}

# Accessing values
name = person["name"]
age = person.get("age")

# Adding/updating
person["email"] = "john@example.com"

age = 25

if age >= 18:
    print("Adult")
elif age >= 13:
    print("Teenager")
else:
    print("Child")

# Loop through list
for number in [1, 2, 3, 4, 5]:
    print(number)

# Loop with range
for i in range(5):
    print(i)

# Loop through dictionary
for key, value in person.items():
    print(f"{key}: {value}")

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

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

# Calling function
message = greet("Python")
print(message)

def calculate_total(price, quantity, tax_rate=0.1):
    subtotal = price * quantity
    tax = subtotal * tax_rate
    total = subtotal + tax
    return total

# Calling with positional arguments
total1 = calculate_total(10, 5)

# Calling with keyword arguments
total2 = calculate_total(price=10, quantity=5, tax_rate=0.15)

def get_stats(numbers):
    total = sum(numbers)
    average = total / len(numbers)
    return total, average

total, avg = get_stats([1, 2, 3, 4, 5])

# Traditional way
squares = []
for x in range(10):
    squares.append(x**2)

# List comprehension
squares = [x**2 for x in range(10)]

# With condition
even_squares = [x**2 for x in range(10) if x % 2 == 0]

name = "Python"
version = 3.9

# f-strings (preferred)
message = f"Welcome to {name} {version}"

# .format()
message = "Welcome to {} {}".format(name, version)

# Reading file
with open('data.txt', 'r') as file:
    content = file.read()

# Writing file
with open('output.txt', 'w') as file:
    file.write("Hello, World!")

def calculate_statistics(numbers):
    """Calculate mean, min, max of a list"""
    if not numbers:
        return None

    total = sum(numbers)
    count = len(numbers)
    mean = total / count
    minimum = min(numbers)
    maximum = max(numbers)

    return {
        'mean': mean,
        'min': minimum,
        'max': maximum,
        'count': count
    }

# Test it
data = [10, 20, 30, 40, 50]
stats = calculate_statistics(data)
print(stats)