String manipulation

Determine if a string has a given prefix to guide branching logic.

Filtering a collection of strings that start with a certain prefix; validating user input such as file names or URLs; parsing log lines for known prefixes.

General Python scripting, data processing pipelines, web API request handling, CLI utilities.

string_var.startswith(prefix)

str.startswith(...)

string_var: any expression returning a str; prefix: str literal or variable containing the prefix to test

• if statements
• filter()
• list comprehensions
• endswith
• str.contains (via 'in')
• regex match

• s[:len(prefix)] == prefix
• re.match(f'^{re.escape(prefix)}'
• s)
• using str.startswith with a tuple of prefixes

Assuming case-insensitivity (it is case-sensitive by default); applying to None or non-string objects causing AttributeError; confusing with the 'in' operator which checks for a substring anywhere, not just at the start; forgetting that an empty prefix always returns True

str.endswith – checks suffix; str.find – returns index of first occurrence; re.match – regex‑based prefix match

Coming from JavaScript: .startsWith behaves similarly but remember Python’s version is case‑sensitive; from Java: String.startsWith is analogous but Java’s overloads differ.

• str.endswith
• str.find
• str.index
• re.match

Do not use for case‑insensitive prefix checks or when you need to locate the prefix position; it runs in O(len(prefix)) time and O(1) extra space; an empty prefix returns True for any string, including the empty string.

Makes prefix checks explicit and readable, avoiding manual slicing and reducing off‑by‑one errors.

Think of ‘pre’ as a prefix; starts with ‘pre’.

Case-sensitive; returns True for empty prefix; O(len(prefix)) time complexity.

Use str.startswith with a tuple of multiple prefixes; or switch to re.match for more complex prefix patterns.