click.core.Parameter

A parameter to a command comes in two versions: they are either :class:`Option`\s or :class:`Argument`\s. Other subclasses are currently not supported by design as some of the internals for parsing are intentionally not finalized. Some settings are supported by both options and arguments. :param param_decls: the parameter declarations for this option or argument. This is a list of flags or argument names. :param type: the type that should be used. Either a :class:`ParamType` or a Python type. The later is converted into the former automatically if supported. :param required: controls if this is optional or not. :param default: the default value if omitted. This can also be a callable, in which case it's invoked when the default is needed without any arguments. :param callback: A function to further process or validate the value after type conversion. It is called as ``f(ctx, param, value)`` and must return the value. It is called for all sources, including prompts. :param nargs: the number of arguments to match. If not ``1`` the return value is a tuple instead of single value. The default for nargs is ``1`` (except if the type is a tuple, then it's the arity of the tuple). If ``nargs=-1``, all remaining parameters are collected. :param metavar: how the value is represented in the help page. :param expose_value: if this is `True` then the value is passed onwards to the command callback and stored on the context, otherwise it's skipped. :param is_eager: eager values are processed before non eager ones. This should not be set for arguments or it will inverse the order of processing. :param envvar: a string or list of strings that are environment variables that should be checked. :param shell_complete: A function that returns custom shell completions. Used instead of the param's type completion if given. Takes ``ctx, param, incomplete`` and must return a list of :class:`~click.shell_completion.CompletionItem` or a list of strings. .. versionchanged:: 8.0 ``process_value`` validates required parameters and bounded ``nargs``, and invokes the parameter callback before returning the value. This allows the callback to validate prompts. ``full_process_value`` is removed. .. versionchanged:: 8.0 ``autocompletion`` is renamed to ``shell_complete`` and has new semantics described above. The old name is deprecated and will be removed in 8.1, until then it will be wrapped to match the new requirements. .. versionchanged:: 8.0 For ``multiple=True, nargs>1``, the default must be a list of tuples. .. versionchanged:: 8.0 Setting a default is no longer required for ``nargs>1``, it will default to ``None``. ``multiple=True`` or ``nargs=-1`` will default to ``()``. .. versionchanged:: 7.1 Empty environment variables are ignored rather than taking the empty string value. This makes it possible for scripts to clear variables if they can't unset them. .. versionchanged:: 2.0 Changed signature for parameter callback to also be passed the parameter. The old callback format will still work, but it will raise a warning to give you a chance to migrate the code easier.