Saving Data to XDI Files¶
Note
This page is intended for beamline staff. If you are a user at a beamline using Haven, this is most likely already set up for you.
XAFS Data Interchange (XDI) is a standard file format for storing data
from individual XAFS scans in a plain-text file. Currently, Haven
supports automatic saving of energy scans using either the
energy_scan() or
xafs_scan() functions. The filename
used for saving will be generated from metadata. For more refined
control, see below for how to create
XDIWriter objects, or even creating a
customized subclass of XDIWriter.
The XDI file is opened at the start of the scan, and data are written in real time during data acquisition, so aborted plans will still have data saved. Halted plans will still have data saved, but the file may remain open with write intent until the python interpreter running Haven is closed. This was a deliberate design choice to ensure the XDI writer keeps an exclusive lock on the file during execution of the plan.
Using the XDIWriter¶
If you want to save the XDI file to specific place or pass in other
arguments, you can create your own instance of the
XDIWriter class. The first argument to
XDIWriter() should be either a file
name, a pathlib.Path object, or an open file like those
return by python’s built-in open(). The following 3 invocations
are all valid:
from haven import XDIWriter
from pathlib import Path
# Provide a regular string...
writer = XDIWriter("/path/to/my/xafs_data.xdi")
# ...or provide a Path object...
root = Path("/path/to/my/")
writer = XDIWriter(root / "xafs_data.xdi")
The filename can contain placeholders that will be filled in once the plan starts. This works similarly to python’s format string syntax. For example:
from haven import XDIWriter
plan = energy_scan(..., E0="Ni_K", md=dict(sample_name="nickel oxide"))
writer_callback = XDIWriter(fd="./{year}{month}{day}_{sample_name}_{edge}.xdi")
RE(plan, writer)
Assuming the date is 2022-08-19, then the filename will become “20220819_nickel-oxide_Ni_K.xdi”.