Preferences, Graphs and Utilities¶

Preferences¶

A Prefs holds an application’s preferences: it’s an AttributedObject (see Attributes), with no supertypes, saved to a file of its own. An application typically reads it when it starts, and saves it when it quits:

try:
  prefs = MyPrefs.read(path)        # (a subclass of Prefs)
except Exception:
  prefs = MyPrefs()
...
width = prefs.get("gui/width", storeDefault=600, storeType=int,
                  note="The width of a new window.")

Declaring a preference where it’s first used – with storeDefault, its type and a note – adds it, with its default, to the file, where the user can see and change it. applyEditAttrsBox() makes a preferences dialog of it with no further work (see Tk Widgets). prefs.addCallback(key, fn) registers a function to call whenever a preference changes. Since Prefs is Dirtyable, an application can save it only if it’s changed.

Graphs¶

util.abstractGraph is the basis for persistent graphs: an AbstractGraph is a database (see Persistence) of AGObjects, each of which keeps the relations that come in to it and go out from it. A relation, AGRelation, is itself an object, with a src and a dst – either of which may be a node, another relation, or None – and keeps its ends’ lists up to date as it’s connected, reconnected and disconnected. (Semantic Nets’ models and views are both AbstractGraphs.)

The utilities module¶

util.utils is a miscellany. Among other things:

URLs and files: fixURL() (make a file path or URL into a URL, with an extension), isValidURL(), urlExists(), fileToUrl(), urlToFile(), changeUrlExtension().
Classes: getFullClassName() and getClassFromFullyQualifiedName() (how saved files name classes), findConcreteSubclasses(), importSubmodules().
Geometry: Point, pointInRect(), pointInPoly(), overlaps(), expandRect(), normalizeRect(), midpoint().
Tk helpers: bindRightMouse() (a right click, or Control-click on a Mac), askUser() (asks in a Tk dialog if there’s a GUI, or else on the terminal), showExceptionDialog(), VerticalScrolledFrame.
Lists and text: grouped(), flattenPairs(), removeDuplicates(), strToBool(), quoteIfNecessary(), resolveAliases() (${name} substitutions).
Commands: makeParserFromFunc(): an argparse parser from a function’s signature and docstring – what the command parser is built on (see Commands).
Categories: Named categories of objects, each defined by a test (Semantic Nets uses them to hide or erase categories of objects in a view).
ExtendedFlag: A Flag whose members can be looked up by combined names, eg: Flags["A|B"].