Types: _coerce_decimal silently accepts bool → cryptic InvalidOperation #216

Summary

bool is an int subclass in Python, so isinstance(True, (int, float)) is True and the value falls into the int/float branch of _coerce_decimal. Decimal(str(True)) then attempts Decimal('True') and raises decimal.InvalidOperation('[<class ConversionSyntax>]').

That is a confusing low-level error for a foot-gun (passing True for a price or count is almost always a typo — is_yes=True accidentally tabbed into count=True). The SDK should fail clearly.

Location

kalshi/types.py:13-28

Evidence

# kalshi/types.py:22-25
if isinstance(value, (int, float)):
    return Decimal(str(value))   # ← Decimal(str(True)) == Decimal('True') → InvalidOperation

Reproduction:

>>> from kalshi.types import _coerce_decimal
>>> _coerce_decimal(True)
decimal.InvalidOperation: [<class 'decimal.ConversionSyntax'>]

Recommended fix

Add an explicit bool check before the (int, float) branch:

def _coerce_decimal(value: Any) -> Decimal:
    if isinstance(value, Decimal):
        return value
    if isinstance(value, bool):
        raise TypeError(
            "Cannot convert bool to Decimal — bool is an int subclass, "
            "so this is almost always a typo (did you mean count=1?)."
        )
    if isinstance(value, (int, float)):
        return Decimal(str(value))
    ...

Mirror the check in to_decimal. Add unit test: test_coerce_decimal_rejects_bool.

Severity & category

medium / correctness