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iPython has several features useful for inspecting Python objects and object hierarchies, in particular Tab completion/expansion of attributes, very handy in this case for inspecting the structure of Xtc data.

Once you've cloned the LCLS2 PSDM repository and built the executables therein, generate sample Xtc data files and inspect with iPython and psana. These notes are current as of tag Ric-180309c.

Setting Up

Switch to PSDM conda Environment

Return to the PSDM conda environment, if necessary.

# At the top of the PSDM lcls2 git repo
user@host> bash
user@host-BASH> source ./setup_env.sh
(ps-0.1.2) [user@host-BASH]$

Generate a Sample Data File

Generate a file of simple Xtc-formatted dummy data.

In the current release, this generates a 2-event data file.

# Usage: xtcwriter [-f <filename> -t -h]
(ps-0.1.2) [user@host-BASH]$ xtcwriter -f test.xtc

Create a Basic psana Data Import Script

We need a simple script, let's call it quick.py, to execute in the iPython session.

from psana import DataSource

ds = DataSource('test.xtc')

for evt in ds.events():
	pass

Inspecting Xtc Data in iPython

Start iPython and Run Import Script

1. Start iPython.

   Code Block
   (ps-0.1.2) [user@host-BASH]$ ipython Python 3.6.6 |Anaconda, Inc.| (default, Jun 28 2018, 17:14:51) Type 'copyright', 'credits' or 'license' for more information IPython 6.5.0 -- An enhanced Interactive Python. Type '?' for help. In [1]:

2. Run quick.py.

   Code Block
   language py
   # In iPython session In [1]: run quick.py

Examine Data Per Event

With the import script executed, examine the events in the DataSource object. The iPython %who and %whos magic functions are useful at this stage.

1. Take a look at what's in scope.

   Code Block
   language py
   # In iPython session In [2]: %whos Variable Type Data/Info ------------------------------------ DataSource type <class 'psana.datasource.DataSource'> ds DataSource <psana.datasource.DataSou<...>object at 0x7fa4e8838a58> evt Event <psana.event.Event object at 0x7fa4e8838ba8>

2. Query the psana DataSource object for the number of events read from the file.

   Code Block
   language py
   # In iPython session In [3]: list(ds.events()) Out []: [<psana.event.Event at 0x7fa4d811d0f0>, <psana.event.Event at 0x7fa4d811d198>]

3. Store each event so we can inspect them.

   Code Block
   language py
   # In iPython session In []: ev1 = next(ds.events()) In []: ev2 = next(ds.events())

4. Now use Tab completion to look at the psana representation of these events and drill down. Look at the structure inside ev1 (event1) by typing "ev1." at the console and hitting the Tab key to see a list of attributes and methods inside the ev1 object.

   Code Block
   language py
   # In iPython session In []: evt. evt.dgrams evt.next evt.replace evt.to_bytes evt.from_bytes evt.offsets evt.seconds evt.nanoseconds evt.position evt.size

5. To access detector data inside this event, we'll drill down into the datagram associated with the event. Store the event datagram to continue drilling down.

   Code Block
   language py
   # In iPython session In []: ev1.dgrams Out []: [<dgram.Dgram at 0x7f73938206c0>] In []: ev1dg1 = ev1.dgrams In []: ev1dg1 Out []: [<dgram.Dgram at 0x7f73938206c0>]