Build stronger Python instincts.

Count unique words

Return a dictionary of lower-case word counts for a sentence, ignoring repeated whitespace and simple punctuation at word edges.

Find duplicates

Return the repeated values from a list while preserving their first repeated order.

Normalize an email address

Return a normalized email address by trimming surrounding whitespace and lower-casing its local and domain parts. Reject strings without exactly one @ and non-string input with None.

Merge default settings safely

Merge user settings over defaults, but accept only known keys and return a new dictionary. Unknown user keys must be ignored.

Valid parentheses

Determine whether every opening bracket in the input closes in the correct order.

Validate structured records

Model a retry result contract

Call an operation up to attempts times and return a result dictionary containing ok, value or error, and attempts_used. Do not retry KeyboardInterrupt or SystemExit.

Summarize a text file safely

Design summarize_file so it reads UTF-8 text, returns line and word counts, and gives the caller a useful error result for a missing or undecodable file instead of crashing.