A for loop repeatedly executes a block while retrieving items directly from an iterable. Strings yield characters, dictionaries yield keys, and files yield lines, so an explicit index is usually unnecessary. section 2.15 section 11.2
Python’s loop asks the object for an iterator with iter, requests values with next, and stops when the iterator raises StopIteration. This explains why different iterable objects produce different kinds of items. section 11.2
Choose the loop form according to the task:
- Iterate directly when the block performs an action for every item and ignores a return value, such as creating and writing one file per filename. section 8.2
- Use enumerate when each iteration needs both an item and its numeric position; unpack its two-element tuples into separate variables. section 2.15
- Prefer a comprehension when the goal is to transform an iterable into a new list, such as converting words into their lengths. section 8.2
Index items without manual indexing
for index, one_letter in enumerate('abcd'): print(f'{index}: {one_letter}') section 2.15
Practice with repeated input
A number-guessing game repeatedly asks for a guess, reports “Too high,” “Too low,” or “Just right,” and exits only after the correct number is entered. Related practice includes translating each word in a sentence and joining transformed output. section 2.2 section 3.6
