kovidgoyal/kitty · error · ValueError

Not a number: {x} with error: {e}

Error message

Not a number: {x} with error: {e}

What it means

conf.utils.number_with_unit parses strings like '10px'/'3col'; if the numeric part matches the regex but float() fails, it raises ValueError('Not a number: ...'). This is a config-value parser used for e.g. text_fg_override_threshold-style options.

Source

Thrown at kitty/conf/utils.py:78

def to_color_or_none(x: str) -> Color | None:
    return None if x.lower() == 'none' else to_color(x)


def unit_float(x: ConvertibleToNumbers) -> float:
    return max(0, min(float(x), 1))


def signed_unit_float(x: ConvertibleToNumbers) -> float:
    return max(-1, min(float(x), 1))


def number_with_unit(x: str, default_unit: str, *extra_units: str) -> tuple[float, str]:
    if (mat := number_unit_pat.match(x)) is not None:
        try:
            value = float(mat.group(1))
        except Exception as e:
            raise ValueError(f'Not a number: {x} with error: {e}')
        unit = mat.group(2) or default_unit
        if unit != default_unit and unit not in extra_units:
            raise ValueError(f'Not a valid unit: {x}. Allowed units are: {default_unit}, {", ".join(extra_units)}')
        return value, unit
    raise ValueError(f'Invalid number with unit: {x}')


def to_bool(x: str) -> bool:
    return x.lower() in ('y', 'yes', 'true')


class ToCmdline:
    def __init__(self) -> None:
        self.override_env: dict[str, str] | None = None

    def __enter__(self) -> 'ToCmdline':
        return self

View on GitHub (pinned to 6d5d0c4406)

Solutions

1. Use a plain decimal number, optionally with a valid unit
2. Regenerate/normalize the config value programmatically
3. Check for stray characters pasted into the number

Example fix

# before
text_fg_override_threshold 1e999px
# after
text_fg_override_threshold 20

import re
ok = re.fullmatch(r'[+-]?(\d+\.?\d*|\.\d+)([a-z]*)', value.strip()) is not None

try:
    v, u = number_with_unit(x, 'px')
except ValueError as e:
    v, u = default_value, 'px'

When it happens

Trigger: A config value whose number portion is malformed such that regex matches but float conversion throws (extremely large numbers, NaN-like strings depending on the pattern).

Common situations: Hand-edited kitty.conf with unusual numeric spellings; programmatic config generation producing inf/nan.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• Invalid number with unit: {x}
• Not a valid unit: {x}. Allowed units are: {default_unit}, {"
• Unknown key action: {action}
• This should be run as kitten broadcast
• No option named: {k}

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/52838730a2447a28. Report an issue: GitHub.