topic_helpers.py

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# Copyright (c) 2011, Dorian Scholz, TU Darmstadt
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import roslib
import roslib.msgs
from rostopic import get_topic_type
from python_qt_binding.QtCore import qDebug

def get_type_class(type_name):
    if roslib.msgs.is_valid_constant_type(type_name):
        if type_name == 'string':
            return str
        elif type_name == 'bool':
            return bool
        else:
            return type(roslib.msgs._convert_val(type_name, 0))
    else:
        return roslib.message.get_message_class(type_name)

def get_field_type(topic_name):
    """
    Get the Python type of a specific field in the given registered topic.
    If the field is an array, the type of the array's values are returned and the is_array flag is set to True.
    This is a static type check, so it works for unpublished topics and with empty arrays.

    :param topic_name: name of field of a registered topic, ``str``, i.e. '/rosout/file'
    :returns: field_type, is_array
    """
    # get topic_type and message_evaluator
    topic_type, real_topic_name, _ = get_topic_type(topic_name)
    if topic_type is None:
        #qDebug('topic_helpers.get_field_type(%s): get_topic_type failed' % (topic_name))
        return None, False

    message_class = roslib.message.get_message_class(topic_type)
    if message_class is None:
        qDebug('topic_helpers.get_field_type(%s): get_message_class(%s) failed' % (topic_name, topic_type))
        return None, False

    slot_path = topic_name[len(real_topic_name):]
    return get_slot_type(message_class, slot_path)


def get_slot_type(message_class, slot_path):
    """
    Get the Python type of a specific slot in the given message class.
    If the field is an array, the type of the array's values are returned and the is_array flag is set to True.
    This is a static type check, so it works for unpublished topics and with empty arrays.

    :param message_class: message class type, ``type``, usually inherits from genpy.message.Message
    :param slot_path: path to the slot inside the message class, ``str``, i.e. 'header/seq'
    :returns: field_type, is_array
    """
    is_array = False
    fields = [f for f in slot_path.split('/') if f]
    for field_name in fields:
        try:
            field_name, _, field_index = roslib.msgs.parse_type(field_name)
        except roslib.msgs.MsgSpecException:
            return None, False
        if field_name not in getattr(message_class, '__slots__', []):
            #qDebug('topic_helpers.get_slot_type(%s, %s): field not found: %s' % (message_class, slot_path, field_name))
            return None, False
        slot_type = message_class._slot_types[message_class.__slots__.index(field_name)]
        slot_type, slot_is_array, _ = roslib.msgs.parse_type(slot_type)
        is_array = slot_is_array and field_index is None

        message_class = get_type_class(slot_type)
    return message_class, is_array


def is_slot_numeric(topic_name):
    """
    Check is a slot in the given topic is numeric, or an array of numeric values.
    This is a static type check, so it works for unpublished topics and with empty arrays.

    :param topic_name: name of field of a registered topic, ``str``, i.e. '/rosout/file'
    :returns: is_numeric, is_array, description
    """
    field_type, is_array = get_field_type(topic_name)
    if field_type in (int, float):
        if is_array:
            message = 'topic "%s" is numeric array: %s[]' % (topic_name, field_type)
        else:
            message = 'topic "%s" is numeric: %s' % (topic_name, field_type)
        return True, is_array, message

    return False, is_array, 'topic "%s" is NOT numeric: %s' % (topic_name, field_type)