whisker 1.0.3

Whisker Python client library

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.. include:: doc/symbols/isonum.txt

=======
whisker
=======

Python package for Whisker clients.

- Whisker is a TCP/IP-based research control software suite.
See http://www.whiskercontrol.com/

TL;DR
=====

- :code:`pip install whisker`
- Fire up your Whisker server.
- Test with :code:`whisker_test_twisted --server localhost`
and :code:`whisker_test_rawsockets --server localhost`
- Copy/paste the demo config file and demo task under "A complete simple
task" at the end.

Author/licensing
================

By Rudolf Cardinal ([e-mail]).
Copyright |copy| Rudolf Cardinal.
Licensed under a permissive open-source license; see LICENSE.

Usage
=====

There are three styles of Whisker client available. Full worked exampes are
shown below, along with a rationale for their use. The outlines, however,
look like these:

Twisted client (preferred for simple interfaces)
------------------------------------------------

.. code:: python

from twisted.internet import reactor
from whisker.twistedclient import WhiskerTask

class MyWhiskerTask(WhiskerTask):
# ...

w = MyWhiskerTask()
w.connect(...)
reactor.run()

Qt client (preferred for GUI use)
---------------------------------

More complex; see the Starfeeder project example.

Raw socket client (deprecated)
------------------------------

.. code:: python

from whisker.rawsocketclient import Whisker

w = Whisker()
w.connect_both_ports(...)
# ...
for line in w.getlines_mainsocket():
# ...


Rationale
=========

Approaches to sockets and message passing
-----------------------------------------

Whisker allows a multitude of clients in a great many languages -- anything
that can "speak" down a TCP/IP port, such as C++, Visual Basic, Perl, and
Python.

Whisker uses two sockets, a "main" socket, through which the Whisker server
can send events unprompted, and an "immediate" socket, used for sending
commands/queries and receiving immediate replies with a one-to-one
relationship between commands (client |rarr| server) and responses (server |rarr|
client). Consequently, the client must deal with unpredictable events
coming from the server. It might also have to deal with some sort of user
interface (UI) code (and other faster things, like data storage).

C++
~~~

In C++/MFC, sockets get their own thread anyway, and the framework tries to
hide this from you. So the GUI and sockets coexists fairly happily. Many
Whisker tasks use C++, but it's not the easiest thing in the world.

Perl
~~~~

In Perl, I've used only a very basic approach with a manual message loop,
like this:

.. include:: doc/whisker_client_snippet.pl
:code: perl

Python
~~~~~~

In Python, I've used the following approaches:

Manual event loop
:::::::::::::::::
You can use base socket code, and poll the main
socket for input regularly. Simple. But you can forget about
simultaneous UI. Like this:

.. include:: whisker/test_rawsockets.py
:code: python

Non-threaded, event-driven
::::::::::::::::::::::::::

The Twisted library is great for this (https://twistedmatrix.com/). However:

- Bits of it, like Tkinter integration, still don't support Python 3 fully
(as of 2015-12-23), though this is not a major problem (it's easy to
hack in relevant bits of Python 3 support).

- Though it will integrate its event loop (reactor) with several GUI
toolkits, e.g.
http://twistedmatrix.com/documents/current/core/howto/choosing-reactor.html
this can still fail; e.g. with Tkinter, if you open a system dialogue
(such as the standard "Open File..." or "Save As..." dialogues), the
Twisted reactor will stop and wait, which is no good.
This is a much bigger problem.
(More detail on this problem in my dev_notes.txt for the starfeeder
project.)

- So one could use Twisted with no user interaction during the task.

It looks, from the task writer's perspective, like this:

.. include:: whisker/test_twisted.py
:code: python

Multithreading
::::::::::::::

For multithreading we can use Qt (with the PySide bindings). In this approach,
the Whisker task runs in separate threads from the UI. This works well,
though is not without some complexity. The Qt interface is nice, and
can be fairly fancy. You have to be careful with database access if
using SQLite (which is not always happy in a multithreaded context).

Verdict for simple uses
:::::::::::::::::::::::

Use Twisted and avoid any UI code while the task is running.


Database access
---------------

Database backend
~~~~~~~~~~~~~~~~

There are distinct advantages to making SQLite the default, namely:

- It comes with everything (i.e. no installation required);

- Database can be copied around as single files.

On the downside, it doesn't cope with multithreading/multiuser access quite
as well as "bigger" databases like MySQL.

Users will want simple textfile storage as well.

Front end
~~~~~~~~~

The options for SQLite access include direct access:

https://docs.python.org/3.4/library/sqlite3.html

and SQLAlchemy:

http://www.sqlalchemy.org/

Getting fancier, it's possible to manage database structure migrations with
tools like Alembic (for SQLAlchemy), but this may be getting too complicated
for the target end user.

However, the other very pleasantly simple front-end is dataset:

https://dataset.readthedocs.org/en/latest/


User interface
--------------

A GUI can consume a lot of programmer effort. Let's keep this minimal or
absent as the general rule; for more advanced coding, the coder can do
his/her own thing (a suggestion: Qt).


Task configuration
------------------

Much of the GUI is usually about configuration. So let's get rid of all
that, because we're aiming at very simple programming here. Let's just
put config in a simple structure like JSON or YAML, and have the user edit it
separately.

JSON
~~~~

An example program:

.. include:: doc/json_config_example.py
:code: python

The JSON looks like:

.. include:: doc/json_config_demo.json
:code: json

YAML with attrdict
~~~~~~~~~~~~~~~~~~

This can be a bit fancier in terms of the object structure it can represent,
a bit cleaner in terms of the simplicity of the config file, and safer in terms
of security from dodgy config files.

Using an AttrDict allows a cleaner syntax for reading/writing the Python
object.

.. include:: doc/yaml_config_example.py
:code: python

The YAML looks like this:

.. include:: doc/yaml_config_demo.yaml
:code: yaml

A quick YAML tutorial
:::::::::::::::::::::

A key:value pair looks like:

.. code:: yaml

key: value

A list looks like:

.. code:: yaml

list:
- value1
- value2
# ...

A dictionary looks like:

.. code:: yaml

dict:
key1: value1
key2: value2
# ...


Verdict for simple uses
~~~~~~~~~~~~~~~~~~~~~~~

Use YAML with AttrDict.

Package distribution
--------------------

This should be via PyPI, so users can just do:

.. code:: python

pip3 install whisker

# ...

from whisker import ...

A complete simple task
======================

Having done :code:`pip install whisker`, you should be able to do this:

.. include:: doc/demo_config.yaml
:code: yaml

.. include:: doc/demo_simple_whisker_client.py
:code: python

Version history
===============================================================================

* 10 Feb 2016: moved to package format.
* 25 Feb 2016: v0.2.0; "colourlog" renamed "logsupport".
* 25 Nov 2016: v0.3.5
- Python type hints.
- Write "exit_on_exception" exceptions to log, not via print().
- WhiskerOwner offers new pingack_received signal.
* 1 Dec 2016: v0.3.6
- Changed from PySide to PyQt5 (fewer bugs).
* 23 Mar 2017: v0.3.6
- Removed annotations from alembic.py; alembic uses inspect.getargspec(),
which chokes with "ValueError: Function has keyword-only arguments or
annotations...".
- Support PyQt 5.8, including removing calls to QHeaderView.setClickable,
which has gone: https://doc.qt.io/qt-5/qheaderview.html
* 22 Jun 2016: v0.1.10
- Updates for Starfeeder.
* 23 Jun 2016: v0.1.11
- Further updates for Starfeeder; supporting structured handling of
ClientMessage.
* 2017: v1.0
- Update for new cardinal_pythonlib.
* 7 Sep 2017: v1.0.3
- use SQLAlchemy 1.2 pool_pre_ping feature

Known problems
===============================================================================

* 2016-11-25: Syntax check fails because PyCharm 2016.3 type hints go wrong for
generators:
https://youtrack.jetbrains.com/issue/PY-20657#tab=Linked%20Issues
https://youtrack.jetbrains.com/issue/PY-20709