This quick tour will guide you through the first steps on using PyTango.
Before you begin there are some fundamental TANGO concepts you should be aware of.
Tango consists basically of a set of devices running somewhere on the network.
A device is identified by a unique case insensitive name in the format <domain>/<family>/<member>. Examples: LAB-01/PowerSupply/01, ID21/OpticsHutch/energy.
Each device has a series of attributes, properties and commands.
An attribute is identified by a name in a device. It has a value that can be read. Some attributes can also be changed (read-write attributes).
A property is identified by a name in a device. Usually, devices properties are used to provide a way to configure a device.
A command is also identified by a name. A command may or not receive a parameter and may or not return a value when it is executed.
Any device has at least a State and Status attributes and State, Status and Init commands. Reading the State or Status attributes has the same effect as executing the State or Status commands.
Each device as an associated TANGO Class. Most of the times the TANGO class has the same name as the object oriented programming class which implements it but that is not mandatory.
TANGO devices live inside a operating system process called TANGO Device Server. This server acts as a container of devices. A device server can host multiple devices of multiple TANGO classes. Devices are, therefore, only accessible when the corresponding TANGO Device Server is running.
A special TANGO device server called the TANGO Database Server will act as a naming service between TANGO servers and clients. This server has a known address where it can be reached. The machines that run TANGO Device Servers and/or TANGO clients, should export an environment variable called TANGO_HOST that points to the TANGO Database server address. Example: TANGO_HOST=homer.lab.eu:10000
This chapter assumes you have already installed PyTango.
To explore PyTango you should have a running Tango system. If you are working in a facility/institute that uses Tango, this has probably already been prepared for you. You need to ask your facility/institute tango contact for the TANGO_HOST variable where Tango system is running.
If you are working in an isolate machine you first need to make sure the Tango system is installed and running (Tango howtos).
Most examples here connect to a device called sys/tg_test/1 that runs in a TANGO server called TangoTest with the instance name test. This server comes with the TANGO installation. The TANGO installation also registers the test instance. All you have to do is start the TangoTest server on a console:
$ TangoTest test Ready to accept request
if you receive a message saying that the server is already running, it just means that somebody has already started the test server so you don’t need to do anything.
Finally you can get your hands dirty. The first thing to do is start a python console and import the PyTango module. The following example shows how to create a proxy to an existing TANGO device, how to read and write attributes and execute commands from a python console:
>>> import PyTango >>> # create a device object >>> test_device = PyTango.DeviceProxy("sys/tg_test/1") >>> # every device has a state and status which can be checked with: >>> print(test_device.state()) RUNNING >>> print(test_device.status()) The device is in RUNNING state. >>> # this device has an attribute called "long_scalar". Let's see which value it has... >>> data = test_device.read_attribute("long_scalar") >>> # ...PyTango provides a shortcut to do the same: >>> data = test_device["long_scalar"] >>> # the result of reading an attribute is a DeviceAttribute python object. >>> # It has a member called "value" which contains the value of the attribute >>> data.value 136 >>> # Check the complete DeviceAttribute members: >>> print(data) DeviceAttribute[ data_format = SCALAR dim_x = 1 dim_y = 0 has_failed = False is_empty = False name = 'long_scalar' nb_read = 1 nb_written = 1 quality = ATTR_VALID r_dimension = AttributeDimension(dim_x = 1, dim_y = 0) time = TimeVal(tv_nsec = 0, tv_sec = 1399450183, tv_usec = 323990) type = DevLong value = 136 w_dim_x = 1 w_dim_y = 0 w_dimension = AttributeDimension(dim_x = 1, dim_y = 0) w_value = 0] >>> # PyTango provides a handy pythonic shortcut to read the attribute value: >>> test_device.long_scalar 136 >>> # Setting an attribute value is equally easy: >>> test_device.write_attribute("long_scalar", 8776) >>> # ... and a handy shortcut to do the same exists as well: >>> test_device.long_scalar = 8776 >>> # TangoTest has a command called "DevDouble" which receives a number >>> # as parameter and returns the same number as a result. Let's >>> # execute this command: >>> test_device.command_inout("DevDouble", 45.67) 45.67 >>> # PyTango provides a handy shortcut: it exports commands as device methods: >>> test_device.DevDouble(45.67) 45.67 >>> # Introspection: check the list of attributes: >>> test_device.get_attribute_list() ['ampli', 'boolean_scalar', 'double_scalar', '...', 'State', 'Status'] >>>
This is just the tip of the iceberg. Check the DeviceProxy for the complete API.
PyTango comes with an integrated IPython based console called ITango. It provides helpers to simplify console usage. You can use this console instead of the traditional python console. Be aware, though, that many of the tricks you can do in an ITango console cannot be done in a python program.
Since PyTango 8.1 it has become much easier to program a Tango device server. PyTango provides some helpers that allow developers to simplify the programming of a Tango device server.
Before creating a server you need to decide:
In our example we will write a fake power supply device server. The server will be called PowerSupplyDS. There will be a class called PowerSupply which will have attributes:
Here is the code for the PowerSupplyDS.py
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#!/usr/bin/env python # -*- coding: utf-8 -*- """Demo power supply tango device server""" import time import numpy from PyTango import AttrQuality, AttrWriteType, DispLevel, DevState, DebugIt from PyTango.server import Device, DeviceMeta, attribute, command, run from PyTango.server import device_property class PowerSupply(Device): __metaclass__ = DeviceMeta voltage = attribute(label="Voltage", dtype=float, display_level=DispLevel.OPERATOR, access=AttrWriteType.READ, unit="V",format="8.4f", doc="the power supply voltage") current = attribute(label="Current", dtype=float, display_level=DispLevel.EXPERT, access=AttrWriteType.READ_WRITE, unit="A",format="8.4f", min_value=0.0, max_value=8.5, min_alarm=0.1, max_alarm=8.4, min_warning=0.5, max_warning=8.0, fget="get_current", fset="set_current", doc="the power supply current") noise = attribute(label="Noise", dtype=((int,),), max_dim_x=1024, max_dim_y=1024) host = device_property(dtype=str) port = device_property(dtype=int, default_value=9788) def init_device(self): Device.init_device(self) self.__current = 0.0 self.set_state(DevState.STANDBY) def read_voltage(self): self.info_stream("read_voltage(%s, %d)", self.host, self.port) return 9.99, time.time(), AttrQuality.ATTR_WARNING def get_current(self): return self.__current def set_current(self, current): # should set the power supply current self.__current = current @DebugIt() def read_noise(self): return numpy.random.random_integers(1000, size=(100, 100)) @command def TurnOn(self): # turn on the actual power supply here self.set_state(DevState.ON) @command def TurnOff(self): # turn off the actual power supply here self.set_state(DevState.OFF) @command(dtype_in=float, doc_in="Ramp target current", dtype_out=bool, doc_out="True if ramping went well, False otherwise") def Ramp(self, target_current): # should do the ramping return True if __name__ == "__main__": run([PowerSupply])
Before running this brand new server we need to register it in the Tango system. You can do it with Jive (Jive->Edit->Create server):
... or in a python script:
>>> import PyTango >>> dev_info = PyTango.DbDevInfo() >>> dev_info.server = "PowerSupplyDS/test" >>> dev_info._class = "PowerSupply" >>> dev_info.name = "test/power_supply/1" >>> db = PyTango.Database() >>> db.add_device(dev_info)
After, you can run the server on a console with:
$ python PowerSupplyDS.py test Ready to accept request
Now you can access it from a python console:
>>> import PyTango >>> power_supply = PyTango.DeviceProxy("test/power/supply/1") >>> power_supply.state() STANDBY >>> power_supply.current = 2.3 >>> power_supply.current 2.3 >>> power_supply.PowerOn() >>> power_supply.Ramp(2.1) True >>> power_supply.state() ON
Next steps: Check out the PyTango API.