🐍 Python Day 7 CheatSheet

# Variable Assignment
name = "Alice"          # String
age = 25               # Integer  
height = 5.6           # Float
is_student = True      # Boolean

# Type Checking
print(type(name))      # <class 'str'>
print(isinstance(age, int))  # True

# Type Conversion
str_num = "123"
int_num = int(str_num)  # Convert to integer
float_num = float(str_num)  # Convert to float

# Creating Lists
fruits = ["apple", "banana", "orange"]
numbers = [1, 2, 3, 4, 5]
mixed = [1, "hello", 3.14, True]

# List Methods
fruits.append("grape")        # Add to end
fruits.insert(1, "mango")    # Insert at index
fruits.remove("banana")      # Remove by value
popped = fruits.pop()        # Remove last item

# List Operations
print(len(fruits))           # Length
print(fruits[0])             # First item
print(fruits[-1])            # Last item
print(fruits[1:3])           # Slicing

# List Comprehension Preview
squares = [x**2 for x in range(5)]  # [0, 1, 4, 9, 16]

# Creating Tuples
coordinates = (10, 20)
colors = ("red", "green", "blue")
single_item = (42,)  # Note the comma for single item

# Tuple Operations
print(coordinates[0])        # Accessing elements
print(len(colors))          # Length
print("red" in colors)      # Membership test

# Tuple Unpacking
x, y = coordinates          # x=10, y=20
first, *rest = colors       # first="red", rest=["green", "blue"]

# Tuple Methods (only 2!)
numbers = (1, 2, 2, 3, 2)
print(numbers.count(2))     # Count occurrences: 3
print(numbers.index(3))     # Find index of value: 3

# Creating Sets
fruits = {"apple", "banana", "orange"}
numbers = set([1, 2, 3, 2, 1])  # {1, 2, 3} - duplicates removed

# Set Operations
fruits.add("grape")          # Add element
fruits.discard("banana")     # Remove element (no error if not found)
fruits.remove("apple")       # Remove element (error if not found)

# Set Math Operations
set1 = {1, 2, 3, 4}
set2 = {3, 4, 5, 6}

union = set1 | set2          # {1, 2, 3, 4, 5, 6}
intersection = set1 & set2   # {3, 4}
difference = set1 - set2     # {1, 2}
symmetric_diff = set1 ^ set2 # {1, 2, 5, 6}

# Set Methods
print(len(fruits))           # Size
print("apple" in fruits)     # Membership test

# Creating Dictionaries
student = {"name": "Alice", "age": 20, "grade": "A"}
empty_dict = {}
dict_from_pairs = dict([("a", 1), ("b", 2)])

# Dictionary Operations
print(student["name"])       # Access value
student["city"] = "NYC"      # Add new key-value
student["age"] = 21          # Update existing value
del student["grade"]         # Delete key-value pair

# Dictionary Methods
keys = student.keys()        # Get all keys
values = student.values()    # Get all values  
items = student.items()      # Get key-value pairs

# Safe Access
age = student.get("age", 0)  # Returns 0 if key not found
popped = student.pop("city", None)  # Remove and return value

# Dictionary Comprehension Preview
squares = {x: x**2 for x in range(5)}  # {0:0, 1:1, 2:4, 3:9, 4:16}

# If-Elif-Else
score = 85
if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
else:
    grade = "F"

# For Loops
fruits = ["apple", "banana", "orange"]
for fruit in fruits:
    print(fruit)

for i in range(5):           # 0 to 4
    print(i)

for i, fruit in enumerate(fruits):  # Get index and value
    print(f"{i}: {fruit}")

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

# Loop Control
for i in range(10):
    if i == 3:
        continue             # Skip this iteration
    if i == 7:
        break               # Exit loop
    print(i)

# String Creation
name = "Alice"
message = 'Hello World'
multiline = """This is
a multiline
string"""

# String Methods
text = "  Hello Python World  "
print(text.strip())          # Remove whitespace
print(text.lower())          # Convert to lowercase
print(text.upper())          # Convert to uppercase
print(text.replace("Python", "Java"))  # Replace substring

# String Checking
print(text.startswith("Hello"))  # False (whitespace)
print(text.strip().startswith("Hello"))  # True
print("123".isdigit())       # True
print("abc".isalpha())       # True

# String Formatting
name = "Alice"
age = 25
# f-strings (Python 3.6+)
message = f"My name is {name} and I'm {age} years old"
# format() method
message = "My name is {} and I'm {} years old".format(name, age)
# % formatting (older)
message = "My name is %s and I'm %d years old" % (name, age)

# String Slicing
text = "Python"
print(text[0])     # 'P'
print(text[-1])    # 'n'
print(text[1:4])   # 'yth'
print(text[::-1])  # 'nohtyP' (reverse)

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

# Function with Default Parameters
def greet_with_title(name, title="Mr/Ms"):
    return f"Hello, {title} {name}!"

# Function with Multiple Return Values
def get_name_age():
    return "Alice", 25

name, age = get_name_age()  # Tuple unpacking

# Variable Arguments
def sum_all(*args):         # *args for multiple positional arguments
    return sum(args)

def print_info(**kwargs):   # **kwargs for keyword arguments
    for key, value in kwargs.items():
        print(f"{key}: {value}")

# Recursion Example - Factorial
def factorial(n):
    if n <= 1:              # Base case
        return 1
    return n * factorial(n - 1)  # Recursive call

# Recursion Example - Fibonacci
def fibonacci(n):
    if n <= 1:
        return n
    return fibonacci(n-1) + fibonacci(n-2)

# Local vs Global Variables
global_var = "I'm global"

def my_function():
    local_var = "I'm local"
    global global_var
    global_var = "Modified global"
    return local_var

# List Comprehension - Basic
numbers = [1, 2, 3, 4, 5]
squares = [x**2 for x in numbers]  # [1, 4, 9, 16, 25]

# List Comprehension with Condition
evens = [x for x in numbers if x % 2 == 0]  # [2, 4]

# List Comprehension with if-else
result = [x**2 if x % 2 == 0 else x**3 for x in numbers]

# Nested List Comprehension
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
flattened = [num for row in matrix for num in row]  # [1,2,3,4,5,6,7,8,9]

# Dictionary Comprehension
squares_dict = {x: x**2 for x in range(5)}  # {0:0, 1:1, 2:4, 3:9, 4:16}

# Set Comprehension
unique_squares = {x**2 for x in [1, -1, 2, -2]}  # {1, 4}

# Lambda Functions
add = lambda x, y: x + y
print(add(5, 3))  # 8

# Lambda with Built-in Functions
numbers = [1, 2, 3, 4, 5]
squared = list(map(lambda x: x**2, numbers))  # [1, 4, 9, 16, 25]
evens = list(filter(lambda x: x % 2 == 0, numbers))  # [2, 4]

# Sorting with Lambda
students = [('Alice', 85), ('Bob', 90), ('Charlie', 78)]
sorted_by_grade = sorted(students, key=lambda x: x[1])  # Sort by grade

# Lambda in List Comprehension
operations = [(lambda x: x**2), (lambda x: x**3), (lambda x: x**0.5)]
results = [op(4) for op in operations]  # [16, 64, 2.0]