SeleniumHQ/selenium · error · ValueError

{property_name} cannot be less than 0

Error message

{property_name} cannot be less than 0

What it means

After confirming a value is numeric, _validate_num_property rejects any value below zero. Page height/width, margins, and scale must be non-negative. A negative number raises ValueError naming the property. (Scale has its own narrower 0.1–2.0 range check that fires after this for the scale descriptor.)

Source

Thrown at py/selenium/webdriver/common/print_page_options.py:364

                respective values in cm.

        Example:
            self.set_page_size(PageSize.A4)  # A4 predefined size
            self.set_page_size({"height": 15.0, "width": 20.0})  # Custom size
        """
        self._validate_num_property("height", page_size["height"])
        self._validate_num_property("width", page_size["width"])
        self._page["height"] = page_size["height"]
        self._page["width"] = page_size["width"]
        self._print_options["page"] = self._page

    def _validate_num_property(self, property_name: str, value: float) -> None:
        """Helper function to validate some of the properties."""
        if not isinstance(value, (int, float)):
            raise ValueError(f"{property_name} should be an integer or a float")

        if value < 0:
            raise ValueError(f"{property_name} cannot be less than 0")

View on GitHub (pinned to aa36b38e69)

Solutions

1. Use 0 or a positive value; use None/omission for 'unset'.
2. Clamp negative inputs to 0 or skip the assignment when the value is negative.

Example fix

# before
print_options.set_page_size({'height': -1, 'width': 21})  # -1 sentinel -> ValueError

# after
if h is not None and h >= 0:
    print_options.set_page_size({'height': h, 'width': w})

if not isinstance(value, (int, float)) or value < 0:
    raise ValueError(f'{name} must be a non-negative number')
# then set

def is_non_negative_number(v) -> bool:
    return isinstance(v, (int, float)) and not isinstance(v, bool) and v >= 0

try:
    print_options.set_page_size(page_size)
except ValueError:
    page_size = {k: max(0.0, float(v)) for k, v in page_size.items()}
    print_options.set_page_size(page_size)

When it happens

Trigger: Setting print_options.set_page_size({'height': -5, 'width': 21}), page_height = -1.0, or margin_top = -2. Passing a sentinel like -1 meaning 'unset'.

Common situations: Using -1 as an 'unset' marker from config. Sign errors in calculations. Defaulting missing values to -1.

Related errors

• Value of scale should be between 0.1 and 2
• Orientation value must be one of {self.ORIENTATION_VALUES}
• {property_name} should be an integer or a float
• Invalid page size: #{value}
• Custom page size must include :width and :height

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/2a22dff72aea8ec4. Report an issue: GitHub.