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Differences with python version

1. Option object instead of keyword arguments

Python:

# python allows keyword arguments
parser = argparse.ArgumentParser(prog='PROG', usage='%(prog)s [options]')

Javascript:

// keyword arguments are passed as a single `options` object
parser = argparse.ArgumentParser({ prog: 'PROG', usage: '%(prog)s [options]' })

2. Use strings 'int', 'float' or 'str' instead of built-in python types

Python:

parser.add_argument('--foo', type=int)

Javascript:

parser.add_argument('--foo', { type: 'int' })

3. TypeError instead of ValueError

Python raises TypeError or ValueError for various argument errors. Javascript raises TypeError in both cases.

4. FileType() returns a stream

You should be closing it with .close() if available (which doesn't exist for stdin/stdout).

Only basic read and write modes are implemented. Support for the remaining modes will not be added: FileType is deprecated, emits a PendingDeprecationWarning, and is expected to be removed.

5. When class is called as a function, .call is executed

Override Action.call instead of Action.__call__ in inherited classes

6. Limited support for %-formats

  • %s is rendered as String(arg)
  • %r is rendered as util.inspect(arg)
  • %d, %i is rendered as arg.toFixed(0), no precision digits or padding is supported
  • no other formats are implemented yet

7. No gettext support

All error messages are hardcoded.

8. No pickle support

Python's ArgumentParser can be serialized with pickle. JavaScript has no equivalent serialization mechanism, so this behavior is not supported.

9. ArgumentError follows JavaScript error semantics

ArgumentError.message contains the final formatted error message. Unlike Python, separate argument_name and raw message fields are not exposed.

10. Output uses Node.js stream error handling

print_help(file), print_usage(file), and parser error output write messages to the supplied file object. An object without a .write() method is ignored, as in Python. Exceptions thrown by a custom .write() implementation are not suppressed.

Unlike Python file objects, Node.js streams normally report I/O failures through the error event or a write callback rather than by throwing an OSError from .write(). Those errors must be handled on the stream itself.