Pretty Err

A simple library for printing modern, source-annotated error messages.

Features

• source span annotation
• color output
• multiple non-overlapping spans
• zero-width spans

Install

pip install prettyerr

Quickstart

Print out an error report for some example source code

from prettyerr import Error, Pointer, Span, SrcFile

# example source code
src = """\
const repeat = (message:string, times:int) :> string => {
    return message * times
}
result = repeat("hello", "3")
printl(result)
"""

# Locate spans to highlight (.index() here is just for simplicity)
repeat_start = src.index('repeat(')
bad_arg_start = src.index('"3"')
times_span = Span(repeat_start, repeat_start + len('repeat'))
bad_arg_span = Span(bad_arg_start, bad_arg_start + len('"3"'))

# Build and print the error report
report = Error(
    SrcFile.from_text(src, "path/to/example.lang"),
    title="type mismatch for argument `times`",
    pointer_messages=[
        Pointer(span=times_span, message="`repeat` function's second argument `times` expects an 'int'"),
        Pointer(span=bad_arg_span, message="argument given is type 'string'"),
    ],
    hint='Consider changing string literal "3" to integer 3',
)
print(report)

This generates the following error report

Error: type mismatch for argument `times`

    ╭─[path/to/example.lang:4:10]
  4 | result = repeat("hello", "3")
    ·          ──┬───          ─┬─
    ·            │              ╰─ argument given is type 'string'
    ·            ╰─ `repeat` function's second argument `times` expects an 'int'
    ╰───
  help: Consider changing string literal "3" to integer 3

API at a glance

• SrcFile.from_text(body, path=None)
• Span(start, stop) (stop-exclusive)
• Pointer(span=Span(...) | list[Span], message=..., placement=None, color=None)
• Report types: Error, Warning, Info, Hint
• Common fields: title, message, pointer_messages, hint, use_color

Tips

• Disable ANSI colors with use_color=False.
• Raise an exception with Error(...).throw() (raises ReportException).