PyEpics: Epics Channel Access for Python

# Auto-saving: simple save/restore of PVs

The `autosave` module provides simple save/restore functionality for PVs, with the functions `save_pvs()` and `restore_pvs()`, and an `AutoSaver` class. These are similar to the autosave module from synApps for IOCs in that they use a compatible request file which describes the PVs to save, and a compatible save file which holds the saved values. Of course, the reading and writing is done here via Channel Access, and need not be related to an single IOC.

Use of this module requires the pyparsing package to be installed. This is a fairly common third-party python package, included in many package managers, or installed with tools such as easy_install or pip, or downloaded from PyPI

Request and Save file formats are designed to be compatible with synApps autosave. Notably, the file command with macro substitutions are supported, so that one can have a Request like:

    # My.req
    file "SimpleMotor.req", P=IOC:, Q=m1

with a SimpleMotor.req file of:

    # SimpleMotor.req
    $(P)$(Q).VAL
    $(P)$(Q).DIR
    $(P)$(Q).FOFF

which can then be used for many instances of a SimpleMotor. There is, however, no automated mechanism for finding request files. You will need to include these in the working directory or specify absolute paths.

With such a file, simply using:

    import epics.autosave
    epics.autosave.save_pvs("My.req", "my_values.sav")

will save the current values for the PVs to the file my_values.sav. At a later time, these values can be restored with:

    import epics.autosave
    epics.autosave.restore_pvs("my_values.sav")

The saved file will be of nearly identical format as that of the autosave mechanism, and the `restore_pvs()` function can read and restore values using save files from autosave. Note, however, that the purpose here is quite different from that of the standard autosave module (which is designed to save vales so that PVs can be initialized at IOC startup). Using the functions here will really do a `caput()` to the saved values.

autosave.save_pvs(request_file, save_file)

  saves current value of PVs listed in request_file to the save_file

  Parameters:

    - request_file – name of Request file to read PVs to save.

    - save_file – name of file to save values to write values to

  As discussed above, the request_file follows the conventions of the autosave module from synApps.

autosave.restore_pvs(save_file)

  reads values from save_file and restores them for the corresponding PVs

  Parameters:

    save_file – name of file to save values to read data from.

  Note that `restore_pvs()` will restore all the values it can, skipping over any values that it cannot restore.

## `AutoSaver` class

The `AutoSaver` class provides a convenient way to repeatedly save PVs listed in a request file without having to re-connect all of the PVs. The `AutoSaver` retains the PV connections, and provides a simple `save()` method to save the current PV values to a file. By default, that file will be named from the request file and the current time. This allows you to do something like this:

    #!/usr/bin/env python
    # save PVs from a request file once per minute
    import time
    from epics.autosave import AutoSaver
    my_saver = AutoSaver("My.req")

    # save all PVs every minute for a day
    t0 = time.time()
    while True:
        if time.localtime().tm_sec < 5:
            my_saver.save()
            time.sleep(30 - time.localtime().tm_sec)
        if time.time() - t0 > 86400.0:
            break
        time.sleep(0.5)

This will save PVs to files with names like My_2017Oct02_141800.sav

class autosave.AutoSaver(request_file)

  create an Automatic Saver based on a request file.

  Parameters:

    request_file – name of request file

`AutoSaver` has two methods: `read_request_file()` to read a request file, and `save()` to save the results.

autosave.read_request_file(request_file)

  read and parse request file, begin making PV connections

  Parameters:

    request_file – name of request file

autosave.save(save_file=None, verbose=False)

  read current PV values, write save file.

  Parameters:

    - save_file – name of save file or None. If None, the name of the request file and timestamp (to seconds) will be used to build a file name. Note that there is no check for overwriting files.

    - verbose – whether to print results to the screen [default False]

## Supported Data Types

All scalar PV values can be saved and restored with the `autosave` routines. There is some support for waveform (array) data. For example, character waveforms containing for long strings can be saved and restored. In addition, numerical arrays in waveform can be saved and restored. For array data, the results may not be fully compatible with the autosave module.

### Examples

A simple example using the autosave module:

    import epics.autosave
    # save values
    epics.autosave.save_pvs("my_request_file.req",
                            "/tmp/my_recent_save.sav")

    # wait 30 seconds
    time.sleep(30)

    # restore those values back
    epics.autosave.restore_pvs("/tmp/my_recent_save.sav")