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 length_conversion(value, from_type, to_type) in conversions/length_conversion.py:121 when the destination unit fails the same normalization/membership check as from_type. It fires only after from_type already validated, so it pinpoints the second unit: anything not normalizing to mm/cm/m/km/in/ft/yd/mi — e.g. 'to_meter' typo, 'inches2', unsupported 'nm' — raises a ValueError listing valid abbreviations.

Source

Thrown at conversions/length_conversion.py:121

    ValueError: Invalid 'from_type' value: 'wrongUnit'.
    Conversion abbreviations are: mm, cm, m, km, in, ft, yd, mi
    """
    new_from = from_type.lower().rstrip("s")
    new_from = TYPE_CONVERSION.get(new_from, new_from)
    new_to = to_type.lower().rstrip("s")
    new_to = TYPE_CONVERSION.get(new_to, new_to)
    if new_from 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 new_to not in METRIC_CONVERSION:
        msg = (
            f"Invalid 'to_type' value: {to_type!r}.\n"
            f"Conversion abbreviations are: {', '.join(METRIC_CONVERSION)}"
        )
        raise ValueError(msg)
    return (
        value
        * METRIC_CONVERSION[new_from].from_factor
        * METRIC_CONVERSION[new_to].to_factor
    )


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Use the documented abbreviations/full names for the target unit (mm, cm, m, km, in, ft, yd, mi)
2. Validate both units once at startup against METRIC_CONVERSION keys after applying the library's normalization (lower + rstrip('s') + TYPE_CONVERSION)
3. Restrict your UI's unit dropdown to exactly the supported set so invalid targets cannot be selected

Example fix

# before
length_conversion(1, 'm', 'nmi')  # ValueError

# after
length_conversion(1, 'm', 'mi') * 1.15078  # nautical miles via mi if needed

from conversions.length_conversion import METRIC_CONVERSION, TYPE_CONVERSION
def norm(u: str) -> str:
    u = u.lower().rstrip('s')
    return TYPE_CONVERSION.get(u, u)
if norm(to_type) not in METRIC_CONVERSION:
    raise ValueError(f"unsupported unit {to_type!r}; use {sorted(METRIC_CONVERSION)}")

When it happens

Trigger: length_conversion(4, 'inch', 'wrongUnit'), length_conversion(1, 'm', 'nmi') (nautical mile), or swapped-argument calls where a value/label lands in to_type.

Common situations: Unit pairs stored in separate config columns where the target column has dirtier data; plural forms not covered by rstrip('s') (e.g. 'inches' works, 'feet' works via table, but 'metres' fails); UI dropdowns that include units the library does not support.

Related errors

• Invalid 'from_type' value: {from_type!r}.\nConversion abbrev
• Incorrect 'from_type' or 'to_type' value: {from_type!r}, {to
• base must be >= 2
• Input value is not an integer
• Invalid value was passed to the function

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/498c540d99691a16. Report an issue: GitHub.