pathwaycom/pathway · error · TypeError

Incompatible types for {function_name} operation.\nThe types

Error message

Incompatible types for {function_name} operation.\nThe types are: {dtypes}. {Affected column: '{key}'. }You might try casting the id type to pw.Pointer to circumvent this, but this is most probably an error.

What it means

Raised by Pathway's binary-operation type checking (e.g. arithmetic/comparison between columns, joins on keys) when operand dtypes are incompatible — no common supertype exists. The message lists the types, the affected column, and suggests (for pointers) casting the id type to pw.Pointer or (otherwise) casting expressions to Any as an explicit, likely-wrong workaround.

Source

Thrown at python/pathway/internals/table.py:3264

            raising=True,
        )
    except TypeError:
        msg = (
            f"Incompatible types for {function_name} operation.\n"
            + f"The types are: {dtypes}. "
            + (f"Affected column: '{key}'. " if key is not None else "")
        )
        if pointers:
            msg += (
                "You might try casting the id type to pw.Pointer to circumvent this, "
                + "but this is most probably an error."
            )
        else:
            msg += (
                "You might try casting the expressions to Any type to circumvent this, "
                + "but this is most probably an error."
            )
        raise TypeError(msg)

View on GitHub (pinned to fa2f74a464)

Solutions

1. Cast one side so dtypes match: t1.join(t2, t1.key.cast(str) == t2.key) or use cast_to_types before the operation
2. For id/pointer mismatches, unify id types: t1.update_id_type(pw.Pointer()) or rebuild ids from the same value type
3. As a last resort for genuinely heterogeneous data, cast both to Any as the message suggests — but treat it as a smell
4. Inspect dtypes first: t.eval_type(pw.this.col) on each operand to see the exact mismatch

Example fix

# before
t3 = t1.join(t2, t1.key == t2.key)  # Pointer[int] vs Pointer[str] -> TypeError

# after
t3 = t1.join(t2, t1.key.cast(str).is_in(t2.key))
# or unify id types
t3 = t1.update_id_type(pw.Pointer()).join(t2, pw.left.id == pw.right.id)

from pathway.internals import dtype as dt

def operands_compatible(a, b) -> bool:
    try:
        dt.types_lattice_common_type_binary(a, b)
        return True
    except TypeError:
        return False

def common_type_exists(dtype_getter, *exprs):
    from pathway.internals import dtype as dt
    ds = [dtype_getter(e) for e in exprs]
    try:
        dt.types_lattice_common_type_many(ds)
        return True
    except TypeError:
        return False

try:
    t3 = t1.join(t2, t1.k == t2.k)
except TypeError as e:
    if 'Incompatible types' in str(e):
        t3 = t1.join(t2, t1.k.cast(str) == t2.k.cast(str))

When it happens

Trigger: t1.join(t2, t1.id == t2.id) where id dtypes are different Pointer subtypes; pw.this.a + pw.this.b with int and str columns; comparing columns whose dtypes have no common supertype.

Common situations: Joining tables from different connectors with differently typed key columns; performing arithmetic on mixed-type columns after schema changes; ids built from different value types across pipelines.

Related errors

• direction argument of join should be of type asof_join.Direc
• The behavior argument of join should be of type pathway.temp
• The interval argument of a join should be of a type pathway.
• Join received extra kwargs. You probably want to use TableLi
• invalid expression in restricted context

AI-assisted analysis of pathwaycom/pathway@fa2f74a464 (2026-08-15). Data as JSON: /api/errors/c7b9bb10b85b50d6. Report an issue: GitHub.