TheAlgorithms/Python · error · ValueError

Invalid 'to_type' value: {to_type!r}.\nConversion abbreviati

Error message

Invalid 'to_type' value: {to_type!r}.\nConversion abbreviations are: {', '.join(METRIC_CONVERSION)}

What it means

Raised by conversions/astronomical_length_scale_conversion.py when the target unit (to_type) is not a recognized abbreviation in METRIC_CONVERSION after the same sanitization as from_type (lowercase, strip trailing 's', UNIT_SYMBOL alias lookup). It fires only after from_type has already validated, so the source unit was fine.

Source

Thrown at conversions/astronomical_length_scale_conversion.py:90

    from_sanitized = from_type.lower().strip("s")
    to_sanitized = to_type.lower().strip("s")

    from_sanitized = UNIT_SYMBOL.get(from_sanitized, from_sanitized)
    to_sanitized = UNIT_SYMBOL.get(to_sanitized, to_sanitized)

    if from_sanitized not in METRIC_CONVERSION:
        msg = (
            f"Invalid 'from_type' value: {from_type!r}.\n"
            f"Conversion abbreviations are: {', '.join(METRIC_CONVERSION)}"
        )
        raise ValueError(msg)
    if to_sanitized not in METRIC_CONVERSION:
        msg = (
            f"Invalid 'to_type' value: {to_type!r}.\n"
            f"Conversion abbreviations are: {', '.join(METRIC_CONVERSION)}"
        )
        raise ValueError(msg)
    from_exponent = METRIC_CONVERSION[from_sanitized]
    to_exponent = METRIC_CONVERSION[to_sanitized]
    exponent = 1

    if from_exponent > to_exponent:
        exponent = from_exponent - to_exponent
    else:
        exponent = -(to_exponent - from_exponent)

    return value * pow(10, exponent)


if __name__ == "__main__":
    from doctest import testmod

    testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Use the exact abbreviation listed in the error message for to_type, e.g. convert('1', 'km', 'ly')
2. Validate both units against the module's METRIC_CONVERSION keys before calling
3. Normalize external input (strip whitespace/punctuation) before passing

Example fix

# before
convert('1', 'au', 'kilometers')
# ValueError: Invalid 'to_type' value: 'kilometers'.

# after
convert('1', 'au', 'km')

from conversions.astronomical_length_scale_conversion import METRIC_CONVERSION
to = to_type.lower().strip().removesuffix('s')
if to not in METRIC_CONVERSION:
    to = 'm'  # safe default or raise

def is_valid_unit(unit: str) -> bool:
    from conversions.astronomical_length_scale_conversion import METRIC_CONVERSION
    return isinstance(unit, str) and unit.lower().strip().removesuffix('s') in METRIC_CONVERSION

try:
    convert(value, from_type, to_type)
except ValueError as e:
    if "'to_type'" in str(e):
        raise ValueError('check target unit spelling') from e
    raise

When it happens

Trigger: convert('1', 'km', 'lightyear') when the accepted key is 'ly'; convert('1', 'm', 'pc.') with trailing punctuation; any target abbreviation not present in METRIC_CONVERSION.

Common situations: Asymmetric unit calls where from_type is correct but to_type uses a full name or wrong abbreviation; forgetting astronomical units are abbreviated ('ly', 'au') while metric prefixes are short ('nm', 'cm').

Related errors

• Invalid 'from_type' value: {from_type!r}.\nConversion abbrev
• Empty string was passed to the function
• Non-binary value was passed to the function
• Non-binary value was passed to the function
• Non-binary value was passed to the function

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/9e674ea9099683ff. Report an issue: GitHub.