pola-rs/polars · error · TypeError

`n` parameter of `repeat expected a `int` or `Expr` got a

Error message

`n` parameter of `repeat expected a `int` or `Expr` got a `{qualified_type_name(n)}`

What it means

`pl.repeat`'s `n` must be an int or an Expr; after coercing ints, polars checks the value actually has an underlying `_pyexpr`. Any other type (float, str, list, None, numpy scalar treated as neither) fails this check.

Solutions

1. Pass `n` as a Python `int`, e.g. `n=3`, or wrap non-int scalars: `n=pl.lit(3)`
2. Convert numpy integers: `n=int(np_val)`
3. If n is dynamic, build an expression: `n=pl.col('len')` or `pl.lit(other_col)`

Example fix

// before
pl.repeat(0, n=5.0)
// after
pl.repeat(0, n=5)  # or n=pl.lit(n_int)

if not isinstance(n, int) and not hasattr(n, '_pyexpr'):
    raise TypeError(f'n must be int or Expr, got {type(n)}')

def is_valid_n(n) -> bool:
    return isinstance(n, int) or hasattr(n, '_pyexpr')

try:
    expr = pl.repeat(value, n=n)
except TypeError as e:
    if '`n` parameter' in str(e):
        expr = pl.repeat(value, n=pl.lit(int(n)))
    else:
        raise

When it happens

Trigger: `pl.repeat(value, n=3.0)` (float), `n='3'` (str), `n=np.int64(3)` if not converted, or passing a Series/other object without `_pyexpr`.

Common situations: n coming from JSON/config as a float; passing a Python str thinking it will be parsed as an expression; numpy integer types.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• 'length' must be an integer, string, or expression, not
• list.to_struct() got a str instead of a list. hint: pass
• 'offset' must be an integer, string, or expression, not
• "pad_end" expects a `str`, given a
• "pad_start" expects a `str`, given a

AI-assisted analysis of pola-rs/polars@fe841f959e (2026-09-18). Data as JSON: /api/errors/43a76aaa73894a80. Report an issue: GitHub.

Appendix: source

Thrown at py-polars/src/polars/functions/repeat.py:144

            "z"
    ]

    Generate a Series directly by setting `eager=True`.

    >>> pl.repeat(3, n=3, dtype=pl.Int8, eager=True)
    shape: (3,)
    Series: 'literal' [i8]
    [
            3
            3
            3
    ]
    """
    if isinstance(n, int):
        n = F.lit(n)
    if not hasattr(n, "_pyexpr"):
        msg = f"`n` parameter of `repeat expected a `int` or `Expr` got a `{qualified_type_name(n)}`"
        raise TypeError(msg)
    value_pyexpr = parse_into_expression(value, str_as_lit=True, dtype=dtype)
    expr = wrap_expr(plr.repeat(value_pyexpr, n._pyexpr, dtype))
    if eager:
        return F.select(expr).to_series()
    return expr


@overload
def ones(
    n: int | Expr,
    dtype: PolarsDataType = ...,
    *,
    eager: Literal[False] = ...,
) -> Expr: ...


@overload
def ones(

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