Loops

🟢 NORMAL 

Use when you want to loop directly over the items (values only).

Input	Example	Output
["apple", "banana"]	for fruit in ["apple", "banana"]: print(fruit)	apple banana
"hi"	for char in "hi": print(char)	h i
{ "a": 1, "b": 2 }	for key in {"a": 1, "b": 2}: print(key)	a b
dict.items()	for k, v in {"a": 1}.items(): print(k, v)	a 1

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🔷 RANGE LOOPS

Use when you need to count, index, or control the steps of iteration.

Input	Example	Output
range(3)	for i in range(3): print(i)	0 1 2
range(2, 5)	for i in range(2, 5): print(i)	2 3 4
range(0, 6, 2)	for i in range(0, 6, 2): print(i)	0 2 4
range(3, 0, -1)	for i in range(3, 0, -1): print(i)	3 2 1
range(len(list))	for i in range(len(fruits)): print(fruits[i])	values in fruits

 

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🟣 ENUMERATE LOOPS

Use when you want both index and value from a list or iterable.

Input	Example	Output
["x", "y"]	for i, v in enumerate(["x", "y"]): print(i, v)	0 x 1 y
["a", "b", "c"]	for i, letter in enumerate(["a", "b", "c"]): ...	0 a 1 b 2 c

🧱 NESTED LOOPS 

Loop Type	Input	Example	Output
🔷 Range	range(2), range(2)	for i in range(2): for j in range(2): print(i, j)	0 0, 0 1, 1 0, 1 1
🔷 Range	2D array (matrix) by index	for i in range(len(matrix)):for j in range(len(matrix[0])):	Access each matrix[i][j]
🔷 Range	All pairs in list	for i in range(len(nums)):for j in range(i+1, len(nums)):	Pairs (i, j)
🟣 Enumerate	List of lists (2D grid)	for i, row in enumerate(grid):for j, val in enumerate(row):	(i, j, val) per cell
🟢 Normal	List of lists (values only)	for row in matrix:for val in row: print(val)	Each cell value
🟢 Normal	Two arrays (cross product)	for a in ["a", "b"]:for n in ["1", "2"]: print(a, n)	a 1, a 2, b 1, b 2

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1. ✅ Standard for loop

Use when you want to iterate over items in a list, set, or string.

colors = ['red', 'green', 'blue']
for color in colors:
    print(color)

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2. ✅ enumerate() loop

Use when you need both the index and the value.

for i, color in enumerate(colors):
    print(i, color)

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3. ✅ range() loop

Use when you want to:

• Loop a specific number of times

• Access list items by index

• Do nested loops

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4. ✅ while loop

Use when:

• You don’t know how many times you’ll loop

• You’re waiting for a condition to change

x = 0
while x < 5:
    print(x)
    x += 1

📌 Warning: Always make sure the condition will eventually become False or you'll get an infinite loop!

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🧠 When to Use Which?

Loop Type	When to Use
for item in list	Clean, readable, item-based loops
enumerate()	Index + value
range()	Loop by number or index, brute-force logic
while	Loop while a condition is true (uncertain end)

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Optional Daily Practice Prompts

Want to write one of each daily?

• ✅ for item in list: print all characters in "hello"

• ✅ enumerate(): print index and item of a fruit list

• ✅ range(): print numbers 1 to 10

• ✅ while: count down from 5 to 0

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Want me to add this to your daily fundamentals checklist or export it as a mini Anki flashcard set or markdown file you can keep open?