String methods, character by character
Interactive lab
Try it: String methods, character by character
How Python's str methods (split, strip, replace, find, count, startswith, join, in …) scan a string character by character — and that each call returns a new value while the original string never changes.
How it works
- Each method call reads the string it is called on from left to right (strip also trims from the right end).
- split() with no separator skips runs of whitespace and never returns empty strings; split(sep) cuts at every occurrence of sep and can return empty pieces; maxsplit limits the number of cuts.
- find, index, count, replace and `in` slide a window along the string; occurrences never overlap, find gives -1 and index raises ValueError when nothing matches.
- strip(chars) removes any of the given characters (a set, not a substring) from the ends until it meets one that is not in the set.
- Strings are immutable: every call returns a new str, list, int or bool, and the next call in the chain works on that new value.
Default run (62 steps): s = ' Apples, pears,,figs '. Evaluate ' | '.join(s.strip().lower().split(',')) one method call at a time, left to right. … ' | '.join(s.strip().lower().split(',')) → 'apples | pears | | figs'. And s is still ' Apples, pears,,figs '.
Simplified: Printable ASCII text up to 30 characters and up to four chained calls with short arguments. CPython searches with a faster algorithm (fastsearch) than the window-by-window scan shown, but the results are the same.
Educational simulation
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