SeleniumHQ/selenium · error · ArgumentError

Page size must be a Symbol or a Hash

Error message

Page size must be a Symbol or a Hash

What it means

page_size= only accepts a Symbol (predefined size) or a Hash (custom size). Any other type — String, Array, Integer, nil — raises ArgumentError. This is the catch-all branch of the case statement after the Symbol and Hash branches.

Source

Thrown at rb/lib/selenium/webdriver/common/print_options.rb:88

          letter: {width: 21.59, height: 27.94},
          legal: {width: 21.59, height: 35.56},
          a4: {width: 21.0, height: 29.7},
          tabloid: {width: 27.94, height: 43.18}
        }

        case value
        when Symbol
          raise ArgumentError, "Invalid page size: #{value}" unless predefined_sizes.key?(value)

          @page_size = predefined_sizes[value]
        when Hash
          unless value.key?(:width) && value.key?(:height)
            raise ArgumentError, 'Custom page size must include :width and :height'
          end

          @page_size = value
        else
          raise ArgumentError, 'Page size must be a Symbol or a Hash'
        end
      end
    end
  end
end

View on GitHub (pinned to aa36b38e69)

Solutions

1. Use a predefined Symbol (:a4) or a Hash ({ width:, height: }).
2. Convert incoming data: if it is a String matching a known size, use .to_sym; otherwise build a Hash.
3. Avoid passing Arrays or Strings; map them to the supported types first.

Example fix

# before
print_options.page_size = 'A4'

# after
print_options.page_size = :a4

raise ArgumentError, 'page size must be Symbol or Hash' unless value.is_a?(Symbol) || value.is_a?(Hash)

def valid_page_size?(value)
  value.is_a?(Symbol) || value.is_a?(Hash)
end

begin
  print_options.page_size = value
rescue ArgumentError => e
  raise unless e.message.include?('Symbol or a Hash')
  print_options.page_size = value.to_sym
end

When it happens

Trigger: Passing a String like page_size = 'A4'. Passing an Array [21, 29]. Passing an Integer or nil.

Common situations: Assuming a String size name is accepted. Providing a tuple/array from external data. Defaulting to nil accidentally.

Related errors

• Invalid page size: #{value}
• Custom page size must include :width and :height
• #{scroll_origin.inspect} isn't a valid ScrollOrigin
• invalid value for expiration date: #{obj.inspect}
• expected String or Symbol, got #{key.inspect}:#{key.class}

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/da92ca14cb37a617. Report an issue: GitHub.