TheAlgorithms/Python · error · ValueError

Invalid 'to_type' value: {to_type!r}. Supported values are:

Error message

Invalid 'to_type' value: {to_type!r}.  Supported values are:
{', '.join(PRESSURE_CONVERSION)}

What it means

Raised by pressure_conversion() in conversions/pressure_conversions.py when to_type is not a key in PRESSURE_CONVERSION (checked after from_type passes). Supported target units are the same set: atm, pascal, bar, kilopascal, megapascal, psi, inHg, torr. The ValueError message lists every valid value.

Source

Thrown at conversions/pressure_conversions.py:73

    >>> pressure_conversion(4, "psi", "torr")
    206.85984
    >>> pressure_conversion(1, "inHg", "atm")
    0.0334211
    >>> pressure_conversion(1, "torr", "psi")
    0.019336718261000002
    >>> pressure_conversion(4, "wrongUnit", "atm")
    Traceback (most recent call last):
        ...
    ValueError: Invalid 'from_type' value: 'wrongUnit'  Supported values are:
    atm, pascal, bar, kilopascal, megapascal, psi, inHg, torr
    """
    if from_type not in PRESSURE_CONVERSION:
        raise ValueError(
            f"Invalid 'from_type' value: {from_type!r}  Supported values are:\n"
            + ", ".join(PRESSURE_CONVERSION)
        )
    if to_type not in PRESSURE_CONVERSION:
        raise ValueError(
            f"Invalid 'to_type' value: {to_type!r}.  Supported values are:\n"
            + ", ".join(PRESSURE_CONVERSION)
        )
    return (
        value
        * PRESSURE_CONVERSION[from_type].from_factor
        * PRESSURE_CONVERSION[to_type].to_factor
    )


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Use an exact supported key for to_type (atm, pascal, bar, kilopascal, megapascal, psi, inHg, torr).
2. Keep a single constant tuple of valid units shared by your UI dropdown and the conversion call so they cannot drift.
3. Map 'mmHg' -> 'torr' (numerically identical) if mercury units are required.

Example fix

# before
pressure_conversion(1, 'atm', 'mmHg')  # ValueError: Invalid 'to_type' value: 'mmHg'

# after
pressure_conversion(1, 'atm', 'torr')  # 0.76 (1 mmHg == 1 torr)

from conversions.pressure_conversions import PRESSURE_CONVERSION

if to_type not in PRESSURE_CONVERSION:
    raise ValueError(f'unsupported target unit {to_type!r}')
pressure_conversion(value, from_type, to_type)

from conversions.pressure_conversions import PRESSURE_CONVERSION

def is_pressure_unit(u: object) -> bool:
    return isinstance(u, str) and u in PRESSURE_CONVERSION

try:
    pressure_conversion(v, f, t)
except ValueError as e:
    if "to_type" in str(e):
        raise UserInputError(f'unknown target unit {t!r}') from e
    raise

When it happens

Trigger: Calling pressure_conversion(1, 'atm', 'mmHg') or pressure_conversion(1, 'atm', 'Bar') — any destination unit misspelled, wrong-cased, or unsupported such as 'mmHg'.

Common situations: Hardcoding a display unit string in a UI that drifted from this library's vocabulary; serializing units through a case-transforming layer (title-casing 'inHg' to 'Inhg'); supporting a unit in your product that this library simply lacks.

Related errors

• Invalid 'from_type' value: {from_type!r} Supported values a
• Incorrect 'from_type' or 'to_type' value: {unit_from!r}, {un
• 'time_value' must be a non-negative number.
• Invalid unit {invalid_unit} is not in {', '.join(time_chart)
• Invalid 'from_type' value: {from_type!r} Supported values a

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/efd2af6795ea2ff5. Report an issue: GitHub.