Python Basics¶

Functions¶

Basic Structure¶

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

greet("Alice")

Default Arguments¶

def greet(name="User"):
    print(f"Hello, {name}!")

Functions as First-Class Citizens¶

In Python, functions are first-class citizens. This means you can use functions as variables, pass them as arguments to other functions, and return them from functions.

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

def caller(func, arg):
    return func(arg)

print(caller(greet, "Alice"))  # Output: Hello, Alice!

Data Types¶

Common Data Types:

int (e.g., age = 25)
float (e.g., height = 5.9)
bool (e.g., is_student = True)
str (e.g., name = "Alice")
list (e.g., nums = [3, 1, 4])
NoneType (e.g., status = None)

Example:

name = "Alice"
age = 25
print(name + " is " + str(age) + " years old.")
print(f"{name} is {age} years old.")

Type Conversion¶

Python provides functions to convert data between types:

num_str = "100"
num = int(num_str)
print(float(num))  # 100.0

Logical Operators¶

and: Returns True if both conditions are True.
or: Returns True if at least one condition is True.
not: Inverts a boolean value.

Truthy and Falsey¶

if []:  # An empty list is False
    print("This won't print.")
if [1, 2]:  # A non-empty list is True
    print("This will print.")

`input()`¶

The input() function allows users to provide input to the program during runtime:

name = input("What is your name? ")
print(f"Hello, {name}!")

age = int(input("Enter your age: "))
print(f"You will be {age + 1} next year!")

File Handling¶

# Writing to a file
with open("example.txt", "w") as file:
    file.write("Hello, Python!")

# Reading from a file
with open("example.txt", "r") as file:
    content = file.read()
    print(content)

Common Python Errors¶

SyntaxError¶

print("Hello)  # Missing closing quotation

TypeError¶

"2" + 2  # Can't add string and integer

NameError¶

print(x)  # x is not defined

IndexError¶

['cat', 'dog', 'rabbit'][3] # IndexError: list index out of range

Comments¶

Single-Line Comments¶

# This is a comment
print("Hello!")  # Another comment

Multi-Line Comments¶

'''
This is a multi-line comment.
Useful for longer explanations.
'''
print("Hello!")