String processing¶

This page collects practical recipes for working with str and bytes.

Split and index safely¶

line = "alice,30,engineer"
parts = line.split(",")

name = parts[0]
age = parts[1]
role = parts[2]

To split on runs of whitespace, as Python's split() with no argument does, use split_whitespace(); split() without a separator returns the whole string as one item:

words = "  alpha   beta ".split_whitespace()   # ["alpha", "beta"]

Note: Indexing panics if out of range. If you need fallible parsing, validate the length before indexing (or use a Result-returning helper function).

Build strings¶

words = ["hello", "world"]
sentence = " ".join(words)
println(sentence.upper())  # HELLO WORLD

Clean input¶

raw_input = "  user@example.com  "
email = raw_input.strip().lower()
println(email)  # user@example.com

strip() trims both ends; there is no one-sided variant, so trim and then split when only one side matters.

Test for a substring¶

needle in text tests whether text contains needle, and needle not in text tests the opposite; the contains method gives the same answer as in.

sentence = "the quick brown fox"

if "quick" in sentence:
    println("Found it!")

Replace text¶

text = "hello world"
println(text.replace("world", "incan"))  # hello incan

Move between text and bytes¶

encode gives the UTF-8 bytes of a str; decode reads UTF-8 bytes back and returns Result[str, ValidationError], so malformed input is handled where the bytes enter the program rather than crashing it. Keep decode strict there, and use errors="replace" only for text you copy for display:

def greet(payload: bytes) -> Result[str, ValidationError]:
    text = payload.decode()?
    return Ok(f"hello, {text}")

def main() -> Result[None, ValidationError]:
    payload: bytes = "héllo".encode()
    println(len(payload))                       # 6
    match greet(payload):
        Ok(line) => println(line)               # hello, héllo
        Err(error) => println(f"{error}")       # invalid-utf8: 'utf-8' codec can't decode bytes: …
    println(b"\xff".decode(errors="replace")?)  # U+FFFD replacement character
    return Ok(None)

The error's code is invalid-utf8 for malformed input, unknown-encoding for a run-time label naming another codec, and unknown-errors-policy for a run-time policy other than "strict" or "replace". Other codecs are not built into str and bytes: files use std.fs (read_text / write_text), and hexadecimal, base64 and similar text formats live in std.encoding.