Loops: while, for, range, break, continue & Patterns

count = 1
while count <= 5:
    print("Count:", count)
    count += 1               # without this line the loop would never end!
print("Done")

# Compound growth: how many years until 1,00,000 doubles at 8%?
amount, years = 100000, 0
while amount < 200000:
    amount *= 1.08
    years += 1
print(f"{years} years -> {amount:,.0f}")          # the 'rule of 72': 72 / 8 = 9 years

attempts = ["abc", "-4", "12"]        # simulated user answers
i = 0
while True:
    answer = attempts[i]; i += 1
    if answer.isdigit() and int(answer) > 0:
        print("Accepted:", answer); break
    print("Invalid:", answer)

for city in ["Pune", "Delhi", "Kochi"]:
    print(city.upper())
for ch in "SQL":
    print(ch, end=" ")
print()

print(list(range(5)), list(range(2, 8)), list(range(10, 0, -3)), list(range(0, 1)))
total = 0
for n in range(1, 101): total += n
print("Sum 1..100 =", total, "| check:", sum(range(1, 101)), "| formula:", 100 * 101 // 2)

products = ["Pen", "Notebook", "Stapler"]
prices = [10, 45, 180]
for i, p in enumerate(products, start=1):         # index and value together
    print(i, p)
for p, price in zip(products, prices):            # walk two lists in parallel
    print(f"{p:<10}{price:>5}")
print(dict(zip(products, prices)))                 # build a dictionary from two lists

for n in range(1, 20):
    if n % 3 != 0: continue            # skip numbers not divisible by 3
    if n > 12: break                    # leave the loop completely
    print(n, end=" ")
print()
for n in range(2, 6):
    if n == 9: break
else:                                    # runs only if the loop finished WITHOUT break
    print("loop completed with no break")

orders = [1200, 450, 3000, 780, 2200]
total, large = 0, []
for amount in orders:
    total += amount
    if amount >= 1000: large.append(amount)
print(total, large, total / len(orders))

sales = [("North", 120), ("South", 95), ("East", 140), ("West", 88)]
best_region, best_value = None, float("-inf")
count_above_100 = 0
for region, value in sales:
    if value > best_value: best_region, best_value = region, value
    if value > 100: count_above_100 += 1
print(best_region, best_value, count_above_100)

def find_first(items, target):
    for i, x in enumerate(items):
        if x == target: return i           # stop at the first match
    return -1
print(find_first(["a", "b", "c"], "c"), find_first(["a", "b"], "z"))

for i in range(1, 4):
    for j in range(1, 4):
        print(i * j, end="\t")
    print()

# Pattern: right triangle of stars
for row in range(1, 6): print("*" * row)

readings = iter([12, 15, 11, -1, 99])           # -1 marks the end
total = 0
for r in readings:
    if r == -1: break
    total += r
print("Total before sentinel:", total)

import pandas as pd, time
s = pd.read_csv("superstore_sales.csv")
t0 = time.perf_counter()
loss_lines = 0
for profit in s["profit"]:                    # plain loop over a column (6,323 values)
    if profit < 0: loss_lines += 1
t1 = time.perf_counter()
vec = (s["profit"] < 0).sum()                  # vectorised: one operation on the whole column
t2 = time.perf_counter()
print(f"loop: {loss_lines} loss-making lines in {1000 * (t1 - t0):.2f} ms | vectorised: {vec} in {1000 * (t2 - t1):.2f} ms")

totals = {}
for region, category, sales in zip(s["region"][:2000], s["category"][:2000], s["sales"][:2000]):
    key = (region, category)
    totals[key] = totals.get(key, 0) + sales
for k in sorted(totals)[:6]: print(k, f"{totals[k]:,.0f}")