We Keep Coding

How to feed the data obtained from rospy.Subscriber data into a variable?

I have written a sample Subscriber. I want to feed the data that I have obtained from the rospy.Subscriber into another variable, so that I can use it later in the program for processing. At the moment I could see that the Subscriber is functioning as I can see the subscribed values being printed when I use rospy.loginfo() function. Although I donot know how to store this data into another varible. I have tried assigning it directly to a variable by using assignment operator '=', but I get error.
I have tried writing a callback function with rospy.loginfo to print the position data from the subscribed object. I have subscribed JointState and it containes, header, position, velocity and effort arrays. using rospy.loginfo I can verify that the subscriber is subscribing. But when i tried to assign it directly to a variable, I get an error.
I am displaying loginfo from a call back function as follows
def callback(data):
rospy.loginfo(data.position)
global listen
listen = rospy.Subscriber("joint_states", JointState,
callback)
rospy.spin()
and this works fine. But when i slightly modify the code to assign the subscribed values, I get following error i.e.
listen1 = rospy.Subscriber("joint_states", JointState,
callback=None)
listen = listen1.position
#rospy.loginfo(listen)
print(listen)
rospy.spin()```
The error is as follows,
```listen = listen1.position
AttributeError: 'Subscriber' object has no attribute 'position'
EDIT:
Here is my node I have defined in my program,
#rospy.loginfo(msg.data)
global tactile_states
tactile_states = data.data
def joint_callback(data):
#rospy.loginfo(data.position)
global g_joint_states
global g_position
global g_pos1
g_joint_states = data
#for i in len(data.position):
#g_position[i] = data.position[i]
g_position = data.position
if len(data.position) > 0:
print("jointstate more than 0")
g_pos1 = data.position[0]
#print(g_position)
def joint_modifier(*args):
#choice describes what the node is supposed to do whether act as publisher or subscribe to joint states or tactile sensors
rospy.init_node('joint_listener_publisher', anonymous=True)
pub1 = rospy.Publisher('joint_states', JointState, queue_size = 10)
if(len(args)>1):
choice = args[0]
joint_name = args[1]
position = args[2]
else:
choice = args[0]
if (choice == 1):
rate = rospy.Rate(1)
robot_configuration = JointState()
robot_configuration.header = Header()
robot_configuration.name = [joint_name]
robot_configuration.position = [position]
robot_configuration.velocity = [10]
robot_configuration.effort = [100]
while not rospy.is_shutdown():
robot_configuration.header.stamp = rospy.Time.now()
rospy.loginfo(robot_configuration)
break
pub1.publish(robot_configuration)
rospy.sleep(2)
if (choice == 2):
#rospy.Timer(rospy.Duration(2), joint_modifier)
listen = rospy.Subscriber("joint_states", JointState, joint_callback)
rospy.spin()
if (choice == 3):
#rospy.Timer(rospy.Duration(2), joint_modifier)
tactile_sub = rospy.Subscriber("/sr_tactile/touch/ff", Float64, tactile_callback)
rospy.spin()
This is how I am calling the node inside the main body of the program,
joint_modifier(2)
print("printing g_position")
print(g_position)#to check the format of g_position
print("printed g _position")
leg_1 = Leg_attribute(g_position[0], g_position[1], g_position[2], velocity1 = 10, velocity2 = 10, velocity3 = 10, effort1 = 100, effort2 = 100, effort3 = 100, acceleration=1)
When calling this way, the program is stuck at joint_modifier(2) as that function has rospy.spin().

The style which you're using is not very standard. I assume you've seen the example on ROS wiki, I've modified it to demonstrate standard usage below.
Chiefly, addressing the code you posted, you needed to make listen have global scope outside of the callback. This is to store the data you want, not the Subscriber object. The rospy.spin() never goes in a callback, only the main node function/section. The subscriber object, listen1, which is used infrequently, doesn't return anything, and doesn't store the data it acquires. That is, you need Subscriber() to have a non-None callback.
It's more of a bind, giving the data to the callback instead of returning it from Subscriber. That's why listen1 (Subscriber) has no attribute position (JointState).
import rospy
from sensor_msgs.msg import JointState
# Subscribers
# joint_sub (sensor_msgs/JointState): "joint_states"
# This is where you store all your data you recieve
g_joint_states = None
g_positions = None
g_pos1 = None
def timer_callback(event): # Type rospy.TimerEvent
print('timer_cb (' + str(event.current_real) + '): g_positions is')
print(str(None) if g_positions is None else str(g_positions))
def joint_callback(data): # data of type JointState
# Each subscriber gets 1 callback, and the callback either
# stores information and/or computes something and/or publishes
# It _does not!_ return anything
global g_joint_states, g_positions, g_pos1
rospy.loginfo(data.position)
g_joint_states = data
g_positions = data.position
if len(data.position) > 0:
g_pos1 = data.position[0]
print(g_positions)
# In your main function, only! here do you subscribe to topics
def joint_logger_node():
# Init ROS
rospy.init_node('joint_logger_node', anonymous=True)
# Subscribers
# Each subscriber has the topic, topic type, AND the callback!
rospy.Subscriber('joint_states', JointState, joint_callback)
# Rarely need to hold onto the object with a variable:
# joint_sub = rospy.Subscriber(...)
rospy.Timer(rospy.Duration(2), timer_callback)
# spin() simply keeps python from exiting until this node is stopped
# This is an infinite loop, the only code that gets ran are callbacks
rospy.spin()
# NO CODE GOES AFTER THIS, NONE! USE TIMER CALLBACKS!
# unless you need to clean up resource allocation, close(), etc when program dies
if __name__ == '__main__':
joint_logger_node()
Edit 1:
There seems to be some confusion on what Subscriber(), spin(), and _callback(s) do.
It's a bit obscured in the Python, but there is a master program that manages all nodes, and sending nodes between them. In each node, we register with that master program that the node exists, and what publishers and subscribers it has. By register, it means we tell the master program, "Hey, I want that topic!"; in your case, for your (undeclared) joint_sub Subscriber, "Hey, I want all the JointState msgs from the joint_states topic!" The master program will, every time it gets (from some publisher somewhere) a new joint_states JointState msg, send it to that subscriber.
The subscriber handles, deals with, and processes the msg (data) with a callback: when(!) I receive a message, run the callback.
So the master program receives a new joint_states JointState msg from some publisher. Then it, because we registered a subscriber to it, sends it to this node. rospy.spin() is an infinite loop waiting for that data. This is what it does (kinda-mostly):
def rospy.spin():
while rospy.ok():
for new_msg in get_new_messages from master():
if I have a subscriber to new_msg:
my_subscriber.callback(new_msg)
rospy.spin() is where your callback, joint_callback (and/or timer_callback, etc) actually get called, and executed. It only runs when there is data for it.
More fundamentally, I think because of this confusion, your program structure is flawed; your functions don't do what you think they do. This is how you should make your node.
Make your math-portion (all the real non-ros code), the one doing the NN, into a separate module, and make a function to run it.
If you only want to run it when you receive data, run it in the callback. If you want to publish the result, publish in the callback.
Don't call the main function! The if __name__ == '__main__': my_main_function() should be the only place it gets called, and this will call your code. I repeat: the main function, declaring subscribers/publishers/init/timers/parameters, is only run in if __name__ ..., and this function runs your code. To have it run your code, place your code in a callback. Timer callbacks are handy for this.
I hope this code sample clarifies:
import rospy
from std_msgs.msg import Header
from sensor_msgs.msg import JointState
import my_nn as nn # nn.run(data)
# Subscribers
# joint_sub (sensor_msgs/JointState): "joint_states"
# Publishers
# joint_pub (sensor_msgs/JointState): "target_joint_states"
joint_pub = None
def joint_callback(data): # data of type JointState
pub_msg = JointState() # Make a new msg to publish results
pub_msg.header = Header()
pub_msg.name = data.name
pub_msg.velocity = [10] * len(data.name)
pub_msg.effort = [100] * len(data.name)
# This next line might not be quite right for what you want to do,
# But basically, run the "real code" on the data, and get the
# result to publish back out
pub_msg.position = nn.run(data.position) # Run NN on data, store results
joint_pub.publish(pub_msg) # Send it when ready!
if __name__ == '__main__':
# Init ROS
rospy.init_node('joint_logger_node', anonymous=True)
# Subscribers
rospy.Subscriber('joint_states', JointState, joint_callback)
# Publishers
joint_pub = rospy.Publisher('target_joint_states', JointState, queue_size = 10)
# Spin
rospy.spin()
# No more code! This is not a function to call, but its
# own program! This is an executable! Run your code in
# a callback!
Notice that a python module we design to be a ros node, has no functions to be called. It has a defined structure of callbacks and global data shared between them, all initialized and registered in the main function / if __name__ == '__main__'.

get_triggers() in pytransitions not returning expected output

I am using the pytransitions library (documented here) to implement a Finite State Machine. One of the features outlined is the ability to get a list of the triggers for a specific state. Here is the example as per the documentation:
transitions = [
{ 'trigger': 'melt', 'source': 'solid', 'dest': 'liquid' },
{ 'trigger': 'evaporate', 'source': 'liquid', 'dest': 'gas' },
{ 'trigger': 'sublimate', 'source': 'solid', 'dest': 'gas' },
{ 'trigger': 'ionize', 'source': 'gas', 'dest': 'plasma' }
]
machine = Machine(model=Matter(), states=states, tansitions=transitions)
m.get_triggers('solid')
>>> ['melt', 'sublimate']
Here is a sample of my code that I am trying to run:
from transitions import Machine
states = ['changes ongoing', 'changes complete', 'changes pushed', 'code reviewed', 'merged']
triggers = ['git commit', 'git push', 'got plus2', 'merged']
# Initialize the state machine
git_user = Machine(states=states, initial=states[0], ignore_invalid_triggers=True, ordered_transitions=True)
# Create the FSM using the data provided
for i in range(len(triggers)):
git_user.add_transition(trigger=triggers[i], source=states[i], dest=states[i+1])
print(git_user.get_triggers(states[0]))
Expected Output:
['git commit']
Obtained output:
['to_code reviewed', 'to_changes ongoing', 'git commit', 'to_changes pushed', 'to_merged', 'to_changes complete', 'next_state']
Looking at the given example in the documentation, I should only get back 'git commit'. And that is the functionality I am looking for.
Thanks in advance for the help!

Machine.get_triggers returns all possible transitions. This also includes auto transitions which are added by default. Additionally, the constructor keyword ordered_transitions=True (which is equivalent to calling Machine.add_ordered_transitions()) will add transitions from each state to the next one passed in your states array with the trigger name next_state.
So you end up with a) all auto transitions plus b) one next_state and c) one of your added transitions.
To get your desired result you should disable auto_transitions and also omit the ordered_transitions keyword:
from transitions import Machine
states = ['changes ongoing', 'changes complete', 'changes pushed',
'code reviewed', 'merged']
triggers = ['git commit', 'git push', 'got plus2', 'merged']
# Initialise the state machine
git_user = Machine(states=states, initial=states[0],
ignore_invalid_triggers=True, auto_transitions=False)
# Create the FSM using the data provided
for i in range(len(triggers)):
git_user.add_transition(trigger=triggers[i], source=states[i],
dest=states[i+1])
print(git_user.get_triggers(states[0])) # >>> ['git commit']
You might also want to rethink your trigger and state names if you want to make use of transitions' convenience functions which do not work with names with spaces.
For instance, 'changes_ongoing' would allow you to use git_user.is_changes_ongoing() to check the current state where a trigger named 'git_commit' could also be called directly on the model with git_user.git_commit().

How to automatically re-run a state if transition condition fails?

Im writing screen scraping application in python, using transitions to handle the state machine.
The initial state is looking for a GUI window. When the window has been found, the state machine changes to next state.
Please consider the following code:
class ScreenScrapper(object):
window = None
def is_window_found(self):
return bool(self.window)
def state_look_for_window(self):
window = get_window() # Returns a bitmap object or None if window is not found
self.do_work()
def state_do_work(self):
print('Do some work!')
print('Window er: ', self.window)
states = ['dummy', 'state_look_for_window', 'state_do_work']
transitions = [
{'trigger': 'start', 'source': 'dummy', 'dest': 'state_look_for_window', 'after': 'state_look_for_window'},
{'trigger': 'do_work', 'source': 'state_look_for_window', 'dest': 'state_do_work', 'conditions': 'is_window_found', 'after': 'state_do_work'},
]
screen_scrapper = ScreenScrapper()
Machine(model=screen_scrapper, states=states, transitions=transitions, initial='dummy')
screen_scrapper.start()
In this simple example, the start changes states from dummy to state_look_for_window. The after callback will look for the window and afterwards change state to state_do_work. This transition has the condition is_window_found
Question: How can state_look_for_window be executed again as long as the transition condition is_window_found return False? Please note: I'm only interested in a solution that can be contained within the state machine. In other words, the only code outside must remain screen_scrapper.start().

Since you just need to transition from one state to another you can just do a state transition after checking is_window_found
I think it should look like this
def state_look_for_window(self):
if not is_window_found:
self.state_look_for_window()
else:
window = get_window() # Returns a bitmap object or None if window is not found
self.do_work()

I think you are asking for a 'reflexive transition', which is a trigger having the same State as source and destination.
I would replace your current diagram by another State called 'Window Ready', and specify an internal transition for that state, where you remain cycling inside the same, until the desired Window GUI is found.

How do I get event log information from pyethereum?

I've got some tests that create contracts with pyethereum and do various things with them, but I'm puzzled over how to get information about events they log.
A simplified example:
from ethereum import tester as t
s = t.state()
code = """contract LogTest {
event LogMyNumber(uint);
function LogTest() {
}
function logSomething() {
LogMyNumber(4);
}
}"""
logtest = t.state().abi_contract(code, language='solidity', sender=t.k0)
logtest.logSomething()
#number_i_logged = WHAT DO I DO HERE?
#print "You logged the number %d" % (number_i_logged)
I run this and get:
No handlers could be found for logger "eth.pow"
{'': 4, '_event_type': 'LogMyNumber'}
That json that's getting printed is the information I want, but can someone explain, or point me to an example, of how I might capture it and load it into a variable in python so that I can check it and do something with it? There seems to be something called log_listener that you can pass into abi_contract that looks like it's related but I couldn't figure out what to do with it.

I know you've been waiting for an answer for quite a long time, but in case someone else is wondering, here is goes:
log_listeners you mentioned is the way to go. You can find some sample code using it in pyethereum's tests, and here is your fixed code:
from ethereum import tester as t
s = t.state()
code = """contract LogTest {
event LogMyNumber(uint loggedNumber);
function LogTest() {
}
function logSomething() {
LogMyNumber(4);
}
}"""
c = s.abi_contract(code, language='solidity', sender=t.k0)
o = []
s.block.log_listeners.append(lambda x: o.append(c._translator.listen(x)))
c.logSomething()
assert len(o) == 1
assert o == [{"_event_type": 'LogMyNumber', "loggedNumber": 4}]
number_i_logged = o[0]["loggedNumber"]
print "You logged the number %d" % (number_i_logged)

Get progress by Esky tasks

I'm using Esky with my frozen app. It has the following properties and methods
are available on the Esky class:
app.version: the current best available version.
app.active_version: the currently-executing version, or None
if the esky isn't for the current app.
app.find_update(): find the best available update, or None
if no updates are available.
app.fetch_version(v): fetch the specified version into local storage.
app.install_version(v): install and activate the specified version.
Now, that's nice and all, but I want to show the progress of the download task in my Gui.
How can I achieve that?

wxPython has wrapped Esky in their own SoftwareUpdate method:
https://github.com/wxWidgets/wxPython/blob/master/wx/lib/softwareupdate.py
In their implementation, the application checks for new versions, and asks the user if they'd like to update (using wx GUI for interaction). If the user chooses to update, the code simply calls esky's auto_update() method to handle the rest, but they provide it with an _updateProgress method which updates a progress bar and provides messages indicating Esky's progress:
self._esky.auto_update(self._updateProgress)
...
def _updateProgress(self, status):
# Show progress of the download and install. This function is passed to Esky
# functions to use as a callback.
if self._pd is None and status.get('status') != 'done':
self._pd = wx.ProgressDialog('Software Update', ' '*40,
style=wx.PD_CAN_ABORT|wx.PD_APP_MODAL,
parent=self._parentWindow)
self._pd.Update(0, '')
if self._parentWindow:
self._pd.CenterOnParent()
simpleMsgMap = { 'searching' : 'Searching...',
'retrying' : 'Retrying...',
'ready' : 'Download complete...',
'installing' : 'Installing...',
'cleaning up' : 'Cleaning up...',}
if status.get('status') in simpleMsgMap:
self._doUpdateProgress(True, simpleMsgMap[status.get('status')])
elif status.get('status') == 'found':
self._doUpdateProgress(True, 'Found version %s...' % status.get('new_version'))
elif status.get('status') == 'downloading':
received = status.get('received')
size = status.get('size')
currentPercentage = 1.0 * received / size * 100
if currentPercentage > 99.5:
self._doUpdateProgress(False, "Unzipping...", int(currentPercentage))
else:
self._doUpdateProgress(False, "Downloading...", int(currentPercentage))
elif status.get('status') == 'done':
if self._pd:
self._pd.Destroy()
self._pd = None
wx.Yield()
def _doUpdateProgress(self, pulse, message, value=0):
if pulse:
keepGoing, skip = self._pd.Pulse(message)
else:
keepGoing, skip = self._pd.Update(value, message)
if not keepGoing: # user pressed the cancel button
self._pd.Destroy()
self._pd = None
raise UpdateAbortedError()
The code above was take directly from https://github.com/wxWidgets/wxPython/blob/master/wx/lib/softwareupdate.py.
This feature is documented in the Esky source, file: init.py, line: 689.
The code itself shows what your callback can expect to see throughout an update. Here are some excerpts where your callback would be called:
callback({"status":"searching"})
callback({"status":"found", "new_version":version})
callback({"status":"installing", "new_version":version})
for status in self.sudo_proxy.fetch_version_iter(version):
if callback is not None:
callback(status)
callback({"status":"cleaning up"})
callback({"status":"cleaning up"})
callback({"status":"error","exception":e})
callback({"status":"done"})

Not properly documenated, there is the fetch_version_iter generator function:
fetch_version_iter: like fetch_version but yielding progress updates
during its execution
It yields the following values:
yield {"status": "downloading",
"size": infile_size,
"received": partfile.tell(),
}
yield {"status":"retrying","size":None}
yield {"status":"ready","path":name}
Also, you can get the filename like that:
app.version_finder.version_graph.get_best_path(app.version,v)