String manipulation

Create a modified copy of a string with specific substrings substituted.

Web development: updating URLs to a new domain; File management: changing file extensions from .txt to .md; Data cleaning: sanitizing user input by swapping prohibited tokens

General‑purpose Python scripts, data‑cleaning pipelines, web back‑ends, command‑line utilities.

string.replace(old, new)

...replace(..., ...)

string: str; old: str; new: str

• str.upper()
• str.lower()
• str.strip()
• re.sub()
• f-strings
• str.join()

• Using re.sub for regex‑based replacement
• using str.translate for character‑wise mapping
• chaining multiple replace calls.

Assuming replace mutates the original string; forgetting to assign the returned value; using replace when a regex pattern is needed.

re.sub performs pattern‑based (regex) replacement, while str.replace works on literal substrings; str.translate replaces characters via a translation table.

Coming from languages with mutable strings (e.g., JavaScript), developers may expect an in‑place change.

• String methods
• text processing
• immutability patterns

replace replaces all occurrences unless a third count argument is provided; it is case‑sensitive and works on Unicode code points.

Produces a new string without side effects, making code safer and easier to reason about.

Find‑and‑replace: old → new.

Because strings are immutable in Python, replace always returns a new string; assigning the result is required to effect change.

Use re.sub(pattern, repl, string) for regular‑expression based replacements or str.translate(table) for per‑character mapping.