Python basis

x = 3
print(x, type(x))

print(x + 1)  # Addition
print(x - 1)  # Subtraction
print(x * 2)  # Multiplication
print(x**2)  # Exponentiation

x += 1
print(x)
x *= 2
print(x)

y = 2.5
print(type(y))
print(y, y + 1, y * 2, y**2)

t, f = True, False
print(type(t))

print(t and f)  # Logical AND;
print(t or f)  # Logical OR;
print(not t)  # Logical NOT;
print(t != f)  # Logical XOR;

hello = "hello"  # String literals can use single quotes
world = "world"  # or double quotes; it does not matter
print(hello, len(hello))

hw = hello + " " + world  # String concatenation
print(hw)

hw12 = f"{hello} {world} {12}"  # string formatting
print(hw12)

s = "hello"
print(s.capitalize())  # Capitalize a string
print(s.upper())  # Convert a string to uppercase; prints "HELLO"
print(s.rjust(7))  # Right-justify a string, padding with spaces
print(s.center(7))  # Center a string, padding with spaces
print(s.replace("l", "(ell)"))  # Replace all instances of one substring with another
print("  world ".strip())  # Strip leading and trailing whitespace

xs = [3, 1, 2]  # Create a list
print(xs, xs[2])
print(xs[-1])  # Negative indices count from the end of the list; prints "2"

xs[2] = "foo"  # Lists can contain elements of different types
print(xs)

xs.append("bar")  # Add a new element to the end of the list
print(xs)

x = xs.pop()  # Remove and return the last element of the list
print(x, xs)

nums = list(range(5))  # range is a built-in function that creates a list of integers
print(nums)  # Prints "[0, 1, 2, 3, 4]"
print(nums[2:4])  # Get a slice from index 2 to 4 (exclusive); prints "[2, 3]"
print(nums[2:])  # Get a slice from index 2 to the end; prints "[2, 3, 4]"
print(nums[:2])  # Get a slice from the start to index 2 (exclusive); prints "[0, 1]"
print(nums[:])  # Get a slice of the whole list; prints ["0, 1, 2, 3, 4]"
print(nums[:-1])  # Slice indices can be negative; prints ["0, 1, 2, 3]"
nums[2:4] = [8, 9]  # Assign a new sublist to a slice
print(nums)  # Prints "[0, 1, 8, 9, 4]"

animals = ["cat", "dog", "monkey"]
for animal in animals:
    print(animal)

animals = ["cat", "dog", "monkey"]
for idx, animal in enumerate(animals):
    print(f"#{idx + 1}: {animal}")

nums = [0, 1, 2, 3, 4]
squares = []
for x in nums:
    squares.append(x**2)
print(squares)

nums = [0, 1, 2, 3, 4]
squares = [x**2 for x in nums]
print(squares)

nums = [0, 1, 2, 3, 4]
even_squares = [x**2 for x in nums if x % 2 == 0]
print(even_squares)

d = {"cat": "cute", "dog": "furry"}  # Create a new dictionary with some data
print(d["cat"])  # Get an entry from a dictionary; prints "cute"
print("cat" in d)  # Check if a dictionary has a given key; prints "True"

d["fish"] = "wet"  # Set an entry in a dictionary
print(d["fish"])  # Prints "wet"

print(d["monkey"])  # KeyError: 'monkey' not a key of d

print(d.get("monkey", "N/A"))  # Get an element with a default; prints "N/A"
print(d.get("fish", "N/A"))  # Get an element with a default; prints "wet"

del d["fish"]  # Remove an element from a dictionary
print(d.get("fish", "N/A"))  # "fish" is no longer a key; prints "N/A"

d = {"person": 2, "cat": 4, "spider": 8}
for animal, legs in d.items():
    print(f"A {animal} has {legs} legs")

nums = [0, 1, 2, 3, 4]
even_num_to_square = {x: x**2 for x in nums if x % 2 == 0}
print(even_num_to_square)

animals = {"cat", "dog"}
print("cat" in animals)  # Check if an element is in a set; prints "True"
print("fish" in animals)  # prints "False"

animals.add("fish")  # Add an element to a set
print("fish" in animals)
print(len(animals))  # Number of elements in a set;

animals.add("cat")  # Adding an element that is already in the set does nothing
print(len(animals))
animals.remove("cat")  # Remove an element from a set
print(len(animals))

animals = {"cat", "dog", "fish"}
for idx, animal in enumerate(animals):
    print(f"#{idx + 1}: {animal}")

from math import sqrt

print({int(sqrt(x)) for x in range(30)})

d = {(x, x + 1): x for x in range(10)}  # Create a dictionary with tuple keys
t = (5, 6)  # Create a tuple
print(type(t))
print(d[t])
print(d[(1, 2)])

t[0] = 1

def sign(x):
    if x > 0:
        return "positive"
    elif x < 0:
        return "negative"
    else:
        return "zero"


for x in [-1, 0, 1]:
    print(sign(x))

def hello(name, loud=False):
    if loud:
        print(f"HELLO, {name.upper()}")
    else:
        print(f"Hello, {name}!")


hello("Bob")
hello("Fred", loud=True)

class Greeter:
    # Constructor
    def __init__(self, name):
        self.name = name  # Create an instance variable

    # Instance method
    def greet(self, loud=False):
        if loud:
            print(f"HELLO, {self.name.upper()}")
        else:
            print(f"Hello, {self.name}!")


g = Greeter("Fred")  # Construct an instance of the Greeter class
g.greet()  # Call an instance method; prints "Hello, Fred"
g.greet(loud=True)  # Call an instance method; prints "HELLO, FRED!"