# Tutorial¶

Concert is primarily a user interface to control devices commonly found at a Synchrotron beamline. This guide will briefly show you how to use and extend it.

## Running a session¶

In case you don’t have a beamline at hand, you can fetch our sample sessions with the fetch command:

$concert fetch --repo https://github.com/ufo-kit/concert-examples  Now start the tutorial session: $ concert start tutorial


You will be greeted by an IPython shell loaded with pre-defined devices, processes and utilities like the pint package for unit calculation. Although, this package is primarily used for talking to devices, you can also use it to do simple calculations:

tutorial > a = 9.81 * q.m / q.s**2
tutorial > "Velocity after 5 seconds: {0}".format(5 * q.s * a)

'Velocity after 5 seconds: 49.05 meter / second'


You can get an overview of all defined devices by calling the ddoc() function:

tutorial > ddoc()

------------------------------------------------------------------------------
Name         Description   Parameters
------------------------------------------------------------------------------
motor        None           Name      Access  Unit  Description
position  rw      m     Position of the motor
------------------------------------------------------------------------------
...


Now, by typing just the name of a device, you can see it’s currently set parameter values:

tutorial > motor

<concert.devices.motors.dummy.LinearMotor object at 0x9419f0c>
Parameter  Value
position   12.729455653 millimeter


To get an overview of all devices’ parameter values, use the dstate() function:

tutorial > dstate()

---------------------------------------------
Name         Parameters
---------------------------------------------
motor        position  99.382 millimeter
---------------------------------------------
...


To change the value of a parameter, you simply assign a new value to it:

tutorial > motor.position = 2 * q.mm


Now, check the position to verify that the motor reached the target position:

tutorial > motor.position
<Quantity(2.0, 'millimeter')>


Depending on the device, changing a parameter will block as long as the device has not yet reached the final target state. You can read more about asynchronous execution in the Device control chapter.

Note

A parameter value is always checked for the correct unit and soft limit condition. If you get an error, check twice that you are using a compatible unit (setting two seconds on a motor position is obviously not) and are within the allowed parameter range.

pdoc() displays information about currently defined functions and processes and may look like this:

tutorial > pdoc()
------------------------------------------------------------------------------
Name                   Description
------------------------------------------------------------------------------
save_exposure_scan     Run an exposure scan and save the result as a NeXus
compliant file. This requires that libnexus and NexPy
are installed.
------------------------------------------------------------------------------


In case you are interested in the implementation of a function, you can use code_of(). For example:

tutorial > code_of(code_of)
def code_of(func):
"""Show implementation of *func*."""
source = inspect.getsource(func)

try:
...


Note

Because we are actually running an IPython shell, you can _always_ tab-complete objects and attributes. For example, to change the motor position, you could simply type mo<Tab>.po<Tab> = q.me<Tab>.

## Creating a session¶

First of all, initialize a new session:

$concert init new-session  and start the default editor with $ concert edit new-session


At the top of the file, you can see a string enclosed in three ". This should changed to something descriptive as it will be shown each time you start the session.

To create a device suited for your experiment you have to import it first. Concert uses the following packaging scheme to separate device classes and device implementations: concert.devices.[class].[implementation]. Thus if you want to create a dummy ring from the storage ring class, you would add this line to your session:

from concert.devices.storagerings.dummy import StorageRing


Once imported, you can create the device and give it a name that will be accessible from the command line shell:

from concert.devices.motors.dummy import LinearMotor

ring = StorageRing()
motor = LinearMotor()


### Importing other sessions¶

To specify experiments that share a common set of devices, you can define a base session and import it from each sub-session:

from base import *


Now everything that was defined will be present when you start up the new session.