How to Start Writing Python Code Today (A No-Fluff Guide)

name = "Ava"        # str  — text
age = 19            # int  — whole number
height = 1.72       # float — decimal
is_ready = True     # bool — True or False
score = None        # NoneType — "no value yet"

# f-strings: the clearest way to build strings
print(f"Hello {name}, you are {age} years old.")
# Output: Hello Ava, you are 19 years old.

# Type checking (useful when debugging)
print(type(age))    # <class 'int'>

age = 20

if age >= 21:
    print("Can drink in the US")
elif age >= 18:
    print("Can vote, can't drink yet")
else:
    print("Not yet")

# One-liner (ternary) — only for simple cases
status = "adult" if age >= 18 else "minor"
print(status)   # adult

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

# Loop through every item
for color in colors:
    print(f"I like {color}")

# Loop with index
for i, color in enumerate(colors):
    print(f"{i}: {color}")
# 0: red
# 1: green
# 2: blue

# Add, remove, check
colors.append("yellow")         # add to end
colors.remove("red")            # remove by value
print("green" in colors)        # True

# List comprehension — Pythonic way to build a new list
upper = [c.upper() for c in colors]
print(upper)   # ['GREEN', 'BLUE', 'YELLOW']

user = {
    "name": "Ava",
    "age": 19,
    "skills": ["Python", "SQL"],
}

# Access
print(user["name"])             # Ava
print(user.get("email", "N/A")) # N/A — safe access with default

# Modify
user["age"] = 20
user["email"] = "ava@example.com"

# Iterate
for key, value in user.items():
    print(f"{key}: {value}")

# Check if key exists
if "email" in user:
    print("User has email")

def greet(name: str, title: str = "friend") -> str:
    """Returns a greeting string. title defaults to 'friend'."""
    return f"Hi, {title} {name}!"

print(greet("Ava"))               # Hi, friend Ava!
print(greet("Ava", title="Dr."))  # Hi, Dr. Ava!

# Type hints (str, -> str) are optional but highly recommended
# They make your code easier to read and catch bugs in editors

# Functions can return multiple values (as a tuple)
def min_max(numbers: list[int]) -> tuple[int, int]:
    return min(numbers), max(numbers)

low, high = min_max([3, 1, 4, 1, 5, 9])
print(f"min={low}, max={high}")   # min=1, max=9

def divide(a: float, b: float) -> float:
    if b == 0:
        raise ValueError("Cannot divide by zero")
    return a / b

try:
    result = divide(10, 0)
except ValueError as e:
    print(f"Error: {e}")       # Error: Cannot divide by zero
except ZeroDivisionError:
    print("Zero division caught")
finally:
    print("This always runs")  # cleanup code goes here

# Safe type conversion
user_input = "abc"
try:
    number = int(user_input)
except ValueError:
    print(f"'{user_input}' is not a valid number")

import random
import string

def generate_password(
    length: int = 16,
    use_symbols: bool = True,
    use_numbers: bool = True,
) -> str:
    """
    Generate a random password.
    
    Args:
        length: Number of characters (default 16)
        use_symbols: Include !@#$%^&* (default True)
        use_numbers: Include 0-9 (default True)
    
    Returns:
        A random password string
    """
    # Build character pool
    chars = list(string.ascii_letters)   # a-z, A-Z
    
    if use_numbers:
        chars += list(string.digits)     # 0-9
    
    if use_symbols:
        chars += list("!@#$%^&*")
    
    if len(chars) == 0:
        raise ValueError("No character types selected")
    
    # Shuffle and pick
    password = [random.choice(chars) for _ in range(length)]
    random.shuffle(password)            # extra shuffle for randomness
    return "".join(password)


def main():
    print("=== Password Generator ===\n")
    
    # Get user input with validation
    while True:
        try:
            length = int(input("Password length (8-64, default 16): ") or "16")
            if not 8 <= length <= 64:
                raise ValueError("Length must be between 8 and 64")
            break
        except ValueError as e:
            print(f"Invalid input: {e}. Try again.")
    
    use_symbols = input("Include symbols? (y/n, default y): ").strip().lower() != "n"
    use_numbers = input("Include numbers? (y/n, default y): ").strip().lower() != "n"
    
    # Generate multiple options
    print("\nYour passwords:")
    for i in range(5):
        pwd = generate_password(length, use_symbols, use_numbers)
        print(f"  {i + 1}. {pwd}")
    
    print("\nTip: Copy one and store it in a password manager.")


if __name__ == "__main__":
    main()

# Wrong
if user_input == None:
    ...

# Right
if user_input is None:
    ...

# Wrong — skips items
for item in my_list:
    if item < 0:
        my_list.remove(item)

# Right — iterate a copy
for item in my_list[:]:
    if item < 0:
        my_list.remove(item)

# Wrong — the list persists across calls
def add_item(item, collection=[]):
    collection.append(item)
    return collection

# Right
def add_item(item, collection=None):
    if collection is None:
        collection = []
    collection.append(item)
    return collection

# This floods your terminal — use a counter instead
for i, item in enumerate(large_list):
    if i % 100 == 0:
        print(f"Processing item {i}/{len(large_list)}")