Extracting message type in callback (Python)

rospy

asked 2013-09-02 22:40:23 -0500

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Hey all, I want to extract data of a specific type from the message in the callback. I have only one callback where I get messages from different topics of different type like Float64, Odometry,.etc. Now I want to extract only the data of type Quaternion in side any message of any topic. My call back looks like (although its not correctly working): def callback(self, msg, arg): for m in msg.__slots__: if type(m) == [Quaternion]: self.process(m) but Quaternion is not directly recognized. Also I have to dig into the messages like Odometry has quaternion data but inside the pose.pose.position, how to check the whole structure of message for quaternion datatype data. Thanks in advance,

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Are you sure that you can't find a better/cleaner design for what you want? Seem's kinda odd to me.

dornhege ( 2013-09-03 00:10:14 -0500 )edit

thanks for the suggestion! can you please just write me a hint for the better/cleaner design.I just want to extract Quaternion data xywz (if any) from the msgs, AND I do not know in prior how many topics I shall get and of which type. so I have one generic callback for all the topics...regards

safzam ( 2013-09-03 00:17:06 -0500 )edit

The thing is that I"m not sure why you'd want something like that.

dornhege ( 2013-09-03 01:34:57 -0500 )edit

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thanks for the comment. but msg.__slots__ gives the sub fields names but their type is 'str' rather than Point,.etc. is there any way to dig out the msg structure with type by type dynamically?

safzam ( 2013-09-03 00:20:56 -0500 )edit

There is _slot_types defined for ros msgs.

dornhege ( 2013-09-03 01:34:36 -0500 )edit

yes but it does not help for further digging like I do: for l1 in msg._slot_types: print l1 and output i get [std_msgs/Header,string,geometry_msgs/PoseWithCovariance,geometry_msgs/TwistWithCovariance] but when I want to dig using 'print l1.__slots__' or 'print l1._slot_types' gives error. ?

safzam ( 2013-09-03 03:31:39 -0500 )edit

Hallo donhege, thanks a lot, now it works. the only problem was that 'print l1.__slots__' or 'print l1._slot_types' gives error when datatype encountered is simple and basic datatype because it does not have further substructure. now it works, thank you. regards

safzam ( 2013-09-03 06:49:27 -0500 )edit

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Extracting message type in callback (Python)

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