Iteration

Traverse a sequence element‑by‑element in a clear, readable way.

Processing characters of a string, looping over items in a list, applying an operation to each line of a file.

General‑purpose Python scripts, data‑processing pipelines, educational examples, any codebase that handles iterable collections.

for item in iterable:

for ... in ...:

loop_var: identifier, iterable: expression

• if statements inside the loop
• enumerate()
• list comprehensions
• break/continue statements

• while loop with manual index
• list comprehension for simple transformations

Modifying the iterable while iterating, forgetting the colon, using the wrong variable name inside the block, assuming the loop variable is a single character when iterating over a string of Unicode code points.

while loop (requires manual control of the iterator), list comprehension (creates a new list in a single expression rather than an explicit block).

Coming from C/C++: expecting a char* pointer and manual pointer arithmetic; from JavaScript: expecting a for‑of loop without the 'in' keyword.

• iteration patterns
• string iteration
• for-loop patterns

Prefer this construct for readable, ordered processing of modest‑size iterables; for very large data streams consider generators or itertools to avoid materializing the whole iterable.

Enables iteration over each character in a string, allowing per-character processing such as validation, transformation, or counting.

Iterating over a string is like walking along a string of beads, handling each bead one by one.

Iterating over a string yields its Unicode code points as single‑character strings; iterating over a bytes object yields integer byte values. Strings are immutable, so the iterable cannot be modified during iteration.

Use a list comprehension or generator expression for concise transformations, or employ enumerate for index‑aware loops as the next step.