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Aliases in Bliss

Aliases in Bliss serves the following main purposes:

  • Handle potential duplication of motor names in a beamline-wide configuration

  • Shorten counter names e.g. in the hdf5 files while conserving uniqueness of the keys

Aliases are handled at the global map level within one instance of BLISS. In case they are added dynamically, they are not propagated to other instances, e.g when mulitple BLISS shells are running.

Creation of aliases

Creating aliases through the session yml file

In a session configuration file, a list of aliases can be defined using the aliases keyword. An alias requires the two properties:

  • original_name: (old) name that will be masked by the alias_name
  • alias_name: (new) name that will be assigned to the alias

The alias_name needs to be unique. That means:

  • it can not be used by any object in the configuration,
  • it can not be used as alias name of any other object
  • it can not be used by any object exported to setup_globals

The original_name must be either:

  • an axis object name
  • or a counter fullname
    • counter fullnames are in the form: [master_controller_name:]controller_name:counter_name
    • in the case of a Lima ROI counter, a fullname example would be: pilatus:roi_counters:roi1_std

Aliases will become accessible to the current session env_dict, setup_globals and from the command line, as any other configuration item.

Aliases replace the original object: the original object will be removed from the global namespaces and dictionaries.

Example of a .yml session file containing alias configurations: 

- class: Session
  name: test_alias
  config-objects:
    - simu1
    - roby
    - robz
    - lima_simulator
  aliases:
   - original_name: roby
     alias_name: robyy
   - original_name: simu1:deadtime_det0
     alias_name: dtime

Dynamic creation

Inside a session, aliases can be added at runtime. E.g. one can look at the list of existing counters via lscnt() to see valid counter names available in the session.

TEST_ALIAS [1]: lscnt()

Fullname                          Shape    Controller      Name           Alias
--------------------------------  -------  --------------  -------------  -------
lima_simulator:image              2D       lima_simulator  image
...
simu1:realtime_det0               0D       simu1           realtime_det0  rtime
simu1:realtime_det1               0D       simu1           realtime_det1
...
in order to assign an alias rt1 to simu1.counters.realtime_det1 one can use

ALIASES.add('rt1',simu1.counters.realtime_det1)

from now on the counter is accessible as ‘rt1’ from the command line.

Alias handling

From the BLISS command line all aliases can be managed through 'ALIASES' global object and its methods.

TEST_ALIAS [1]: ALIASES

Alias    Original fullname      
-----   -------------------- 
robyy    roby                
robzz    robz               
dtime    simu1:deadtime_det0
rtime    simu1:realtime_det0
ltime    simu1:livetime_det0
  • ALIASES.add(alias_name, object) adds a new alias dynamically
    • the original object is deleted
    • it is not allowed to make multiple aliases of the same object
    • it is not allowed to make aliases of aliases
  • ALIASES.set(alias_name, object) replaces an alias with a new one pointing to object
  • ALIASES.get(alias_name) returns the alias object corresponding to an alias name
  • ALIASES.get_alias(object) returns the alias name corresponding to object
  • ALIASES.remove(alias_name) removes an existing alias
  • ALIASES.names_iter() returns an iterator over alias names

When adding an alias, the original object gets wrapped into an Alias object:

>>> rt1
<CounterAlias at 0x7f64de481630 with factory <bliss.common.alias.CounterWrapper object at 0x7f64e4680588>>

It exposes all methods and properties from the underlying original object transparently. In addition it provides the following properties:

  • .original_name: the original object name
  • .object_ref: the wrapped original object

Alias in hdf5 output

Running the following scan in a session with configuration given above (test_alias session of the test suite):

a2scan(robyy, 0, 5, robzz, 0, 5, 5, 0.001, dtime, simu1.counters.spectrum_det0)
results in a hdf5 file with the following dump: 
+71_a2scan
    +instrument
        +positioners
            <HDF5 dataset "robyy": shape (), type "<f8">
            <HDF5 dataset "robzz": shape (), type "<f8">
        +positioners_dial
            <HDF5 dataset "robyy": shape (), type "<f8">
            <HDF5 dataset "robzz": shape (), type "<f8">
    +measurement
        <HDF5 dataset "axis:robzz": shape (5,), type "<f8">
        <HDF5 dataset "dtime": shape (5,), type "<f8">
        <HDF5 dataset "axis:robyy": shape (5,), type "<f8">
        <HDF5 dataset "simu1:spectrum_det0": shape (5, 1024), type "<u4">
        <HDF5 dataset "timer:elapsed_time": shape (5,), type "<f8">
    <HDF5 dataset "start_time": shape (), type "|O">
    <HDF5 dataset "title": shape (), type "|O">

In this example we can discuss the following impacts of aliases:

  • The motors are called “robyy” and “robzz” as specified in the aliases tag of the configuration
  • For “robzz” differences can be noted between robzz and robyy:
    • ‘HDF5 dataset “axis:robzz” ‘ for robzz (hide_controller: False)
    • ‘HDF5 dataset “robyy”‘ for robyy (hide_controller: True)
  • The alias dtime is used to shorten the counter name in the output and also when typing the scan command in the shell.

A more detailed look at the hdf5 reveals attributes on each dataset to provide the the systematic names in case they are needed.

71_a2scan/measurement/axis:robzz
    fullname: axis:robz
71_a2scan/measurement/simu1:spectrum_det0
    fullname: simu1:spectrum_det0