Python hypothesis.strategies 模块，none() 实例源码

def field_to_strategy(field, env):
    """Generate strategy for field."""
    if SCALAR_MAPPINGS.get(field.type) is not None:
        return apply_modifier(
            strategy=SCALAR_MAPPINGS[field.type],
            field=field
        )

    if field.type is FieldDescriptor.TYPE_ENUM:
        return apply_modifier(
            strategy=find_strategy_in_env(field.enum_type, env),
            field=field
        )

    if field.type is FieldDescriptor.TYPE_MESSAGE:
        field_options = field.message_type.GetOptions()

        if field_options.deprecated:
            return st.none()

        if field_options.map_entry:
            k, v = field.message_type.fields
            return st.dictionaries(
                field_to_strategy(k, env).filter(non_null),
                field_to_strategy(v, env).filter(non_null)
            )

        return apply_modifier(
            strategy=find_strategy_in_env(field.message_type, env),
            field=field
        )

    raise Exception("Unhandled field {}.".format(field))

def slice_node(draw):
    lower = draw(hs.one_of(const_node(hs.integers()), hs.none()))
    upper = draw(hs.one_of(const_node(hs.integers()), hs.none()))
    step = draw(hs.one_of(const_node(hs.integers()), hs.none()))
    node = astroid.Slice()
    node.postinit(lower, upper, step)
    return node