Using DIRAC Clients From Python


For most tasks it is sufficient to use DIRAC from a terminal via the commands that are prefixed with dirac- or via the WebApp. In some cases however it becomes more convenient to use DIRAC directly from Python.

Before using the DIRAC’s Python API it is useful to understand a few DIRAC-specific concepts.


DIRAC is built around a series of Systems which are independent components and are each contained in a submodule under the main DIRAC import. Examples are:

  • DataManagementSystem for accessing and managing data

  • WorkloadManagementSystem for submitting and managing jobs

Each System contains one or more Clients which can be used for remotely requesting data from DIRAC services. See Remote Procedure Calls.

Return values

Many DIRAC functions return either S_OK() or S_ERROR(). In both of these cases the return value is a dictionary with an OK key which determines if the call was successful.

  • True the object corresponds to S_OK() and contains a Value key with the actual return value.

  • False the object corresponds to S_ERROR() and contains a Message key with a str which should contain more information.

For example, DIRAC contains a utility function for looking up the IP addresses of domains that returns S_OK() or S_ERROR(). This function can be used as follows:

from DIRAC.Core.Utilities.Network import getIPsForHostName

for domain in ["", "fake-domain.invalid"]:
    ret = getIPsForHostName(domain)
    if not ret["OK"]:
        raise RuntimeError(f"Failed to find IPs for {domain}.org with error: {ret['Message']}")
    ips = ret["Value"]
    print(f"{domain} is running at {ips}")

This will print: is running at ['']
Traceback (most recent call last):
File "", line 6, in <module>
    raise RuntimeError(f"Failed to find IPs for {domain}.org with error: {ret['Message']}")
RuntimeError: Failed to find IPs for with error: Can't get info for host fake-domain.invalid: [Errno 8] nodename nor servname provided, or not known

Often when writing user scripts it is useful to immediately raise an exception when an error happens and otherwise just return the value. This makes DIRAC behave more similarly to other Python functions and can be achieved using the helper function returnValueOrRaise(). Rewriting our previous example for looking up IP addressed, this would be:

from DIRAC.Core.Utilities.ReturnValues import returnValueOrRaise
from DIRAC.Core.Utilities.Network import getIPsForHostName

for domain in ["", "fake-domain.invalid"]:
    ips = returnValueOrRaise(getIPsForHostName(domain))
    print(f"{domain} is running at {ips}")

Remote Procedure Calls

Remote Procedure Calls (RPC) describe the process of sending a request to other computers (i.e. DIRAC servers) that triggers them to process something. The result of this remotely ran function is then sent back to the origin of the call (i.e. your computer).

In DIRAC this is done automatically when using the Client classes where calling a method MyClient().something(123) triggers the server to execute a function named export_something(123). See Using a client for an example of using a client.

Initializing DIRAC

Before using Python to contact a service DIRAC’s global state needs to be initialized. Most importantly, this process contacts the Configuration Service and starts a refresher thread. When writing a Python script this should be done using the DIRAC.initialize() function.

import DIRAC


Currently it is essential to call initialize() before importing clients.


If you’re writing a dirac- command initialization should be handled differently. See Developing Commands.

Using a client

Client classes can be found in the Client submodule inside each System module (see Architecture). For example to list job IDs by calling the whoami and getJobs RPC calls:

import DIRAC
from DIRAC.Core.Utilities.ReturnValues import returnValueOrRaise
from DIRAC.WorkloadManagementSystem.Client.JobMonitoringClient import JobMonitoringClient

jmc = JobMonitoringClient()

# Find out who the current user is
my_details = returnValueOrRaise(jmc.whoami())
username = my_details["username"]

# Find the job IDs for the given user
job_ids = returnValueOrRaise(jmc.getJobs({"owner": username}))

print(f"Job IDs for {username} are: {job_ids}")