Variables, Data Types, Type Conversion, print(), f-strings & input()

price = 1250          # an int
tax_rate = 0.18       # a float
product = "Laptop"    # a str
in_stock = True       # a bool
total = price * (1 + tax_rate)
print(product, "costs", total)

a = b = c = 0                 # chained assignment
x, y, z = 1, 2.5, "three"     # multiple assignment (tuple unpacking)
x, y = y, x                   # swap without a temp variable
print(a, b, c, x, y, z)

values = [42, 3.14, "Pune", True, None, 3 + 4j, [1, 2], (1, 2), {"a": 1}, {1, 2}]
for v in values:
    print(f"{str(v):10s} -> {type(v).__name__}")

print(isinstance(42, int), isinstance(True, int), isinstance(3.0, (int, float)))   # True True True
print(type(10 / 2), type(10 // 2))      # / always returns float; // with ints returns int

s = "data"
try:
    s[0] = "D"                     # strings are immutable
except TypeError as e:
    print("Error:", e)
s2 = "D" + s[1:]                    # build a new string instead
print(s2, "| id changed:", id(s) != id(s2))

big = 12_345_678_901_234_567_890 * 10      # ints never overflow
print(big)
print(0.1 + 0.2)                            # floats are approximate!
print(0.1 + 0.2 == 0.3, abs((0.1 + 0.2) - 0.3) < 1e-9)
print(round(2.675, 2), round(0.5), round(1.5), round(2.5))   # banker's rounding: halves go to even

from decimal import Decimal
print(Decimal("0.1") + Decimal("0.2"))                    # exact decimal arithmetic
import math; print(math.isclose(0.1 + 0.2, 0.3))

print(True + True, 5 > 3, 5 == 5.0, "a" < "b", not False)
print(bool(0), bool(0.0), bool(""), bool([]), bool(None))      # all False: "falsy" values
print(bool(1), bool(-3), bool("0"), bool([0]))                  # all True: anything else is "truthy"
print(None is None, type(None))

print(int("42"), int(3.99), int(-3.99), int(True))          # int() truncates towards zero
print(float("3.5"), float(7), float("1e3"))
print(str(123), str(3.0), str([1, 2]))
print(int("1010", 2), int("ff", 16), bin(10), hex(255))     # other bases
print(round(3.7), round(3.14159, 2), int(round(3.7)))

print("5" + 3)                      # TypeError: can only concatenate str to str

print("5" + str(3), int("5") + 3, "5" * 3)      # explicit conversion; repetition for strings

int("abc")                          # ValueError: invalid literal for int()

print(1 + 2.0, True + 1, type(1 + 2.0).__name__)

print("Order", 1001, "shipped")                    # items separated by a space
print("Order", 1001, "shipped", sep=" | ")          # change the separator
print("Loading", end="...")                          # change the line ending (no newline)
print("done")
print("Line one\nLine two\tTabbed")                  # escape sequences: \n newline, \t tab
print('He said "hi"', "It's fine", 'It\'s fine')     # quotes inside strings
print(r"C:\new\table")                                # raw string: backslashes kept
print("""A multi-line
string with triple quotes""")

name, qty, price, share = "Asha", 3, 1234.5678, 0.2345
print(f"{name} bought {qty} items")
print(f"Price: {price:.2f}")                 # 2 decimals
print(f"Price: {price:,.2f}")                # thousands separator
print(f"Share: {share:.1%}")                 # percentage
print(f"ID: {qty:03d}")                       # zero-padded to 3 digits
print(f"[{name:<10}] [{name:>10}] [{name:^10}]")        # left, right, centre in width 10
print(f"{price:>12,.1f}|")                    # right-aligned width 12
print(f"{qty * price:,.2f}  {qty = }")        # expressions work; {x = } prints name and value
print(f"{1234567:,}  {255:#x}  {255:b}  {0.000123:.2e}")

print("{} bought {} items at {:.1f}".format("Asha", 3, 12.345))
print("{1} before {0}".format("B", "A"))
print("{name} paid {amt:,.0f}".format(name="Ravi", amt=1234567))
print("%s bought %d items at %.1f" % ("Asha", 3, 12.345))        # legacy, still seen in old code

name = input("Your name: ")                    # waits for the user
age = int(input("Your age: "))                 # convert to a number
height = float(input("Height in metres: "))
print(f"Hello {name}, you are {age} and {height:.2f} m tall.")

typed = ["Asha", "29", "1.62"]           # imagine the user typed these three answers
name = typed[0]; age = int(typed[1]); height = float(typed[2])
print(f"Hello {name}, you are {age} and {height:.2f} m tall.  In ten years: {age + 10}.")

while True:
    text = input("Enter quantity (1-100): ")
    if text.isdigit() and 1 <= int(text) <= 100:
        quantity = int(text); break
    print("Please type a whole number between 1 and 100.")

nums = [4, 8, 15, 16, 23, 42]
print(len(nums), sum(nums), min(nums), max(nums), sorted(nums, reverse=True))
print(abs(-7), pow(2, 5), divmod(17, 5), round(sum(nums) / len(nums), 2))
print(type(nums).__name__, id(nums) > 0, dir(3)[:3])          # introspection helpers
help(len) if False else None                                   # help(len) prints documentation

items = {"Notebook": (45.0, 10), "Pen pack": (60.0, 25), "Stapler": (180.0, 4)}     # name: (price, quantity)
GST = 0.18
subtotal = 0
print(f"{'Item':<12}{'Price':>8}{'Qty':>5}{'Amount':>10}")
for name, (price, qty) in items.items():
    amount = price * qty; subtotal += amount
    print(f"{name:<12}{price:>8.2f}{qty:>5}{amount:>10,.2f}")
print("-" * 35)
print(f"{'Subtotal':<25}{subtotal:>10,.2f}")
print(f"{'GST (18%)':<25}{subtotal * GST:>10,.2f}")
print(f"{'Total':<25}{subtotal * (1 + GST):>10,.2f}")