TheAlgorithms/Python · error · ValueError

Invalid 'from_type' value: {from_type!r}.\nConversion abbrev

Error message

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

What it means

Raised by conversions/astronomical_length_scale_conversion.py when the source unit (from_type) is not a recognized metric abbreviation after sanitization (lowercased, trailing 's' stripped, alias-mapped via UNIT_SYMBOL). Valid keys are the METRIC_CONVERSION dict entries (m, cm, um/nm-scale prefixes, km, au, ly, etc.). The message lists all accepted abbreviations.

Source

Thrown at conversions/astronomical_length_scale_conversion.py:84

    >>> length_conversion(4, "wrongUnit", "inch")
    Traceback (most recent call last):
      ...
    ValueError: Invalid 'from_type' value: 'wrongUnit'.
    Conversion abbreviations are: m, km, Mm, Gm, Tm, Pm, Em, Zm, Ym
    """

    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)

View on GitHub (pinned to f5988cc097)

Solutions

1. Use the exact abbreviations printed in the error message, e.g. convert('1', 'km', 'm')
2. Strip and lowercase your own input and map full names to abbreviations before calling
3. Check the module's UNIT_SYMBOL dict for supported aliases and use one of those spellings

Example fix

# before
convert('1', 'kilometres', 'meters')
# ValueError: Invalid 'from_type' value: 'kilometres'.

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

from conversions.astronomical_length_scale_conversion import METRIC_CONVERSION
u = from_type.lower().strip().removesuffix('s')
if u not in METRIC_CONVERSION:
    raise ValueError(f'unknown source unit {from_type!r}; valid: {sorted(METRIC_CONVERSION)}')

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 "'from_type'" in str(e):
        raise ValueError('check source unit spelling') from e
    raise

When it happens

Trigger: convert('1', 'meter', 'cm') if 'meter' has no alias (only 'm' or aliases in UNIT_SYMBOL survive); typos like 'kms' -> 'km' is fine but 'kilometre' or 'KM.' fail; passing '' or None.lower()-crashing None actually raises AttributeError first.

Common situations: Passing full unit names instead of abbreviations; locale-specific spellings ('metre', 'kilometer'); trailing punctuation or hidden whitespace (only leading/trailing spaces via strip('s') mishandle ' s'); case is handled, plurals are handled, but arbitrary whitespace inside the string is not.

Related errors

• Invalid 'to_type' value: {to_type!r}.\nConversion abbreviati
• 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/d5d1dc6eeb573369. Report an issue: GitHub.