The Frescobaldi LilyPond sheet music editor is written in Python and uses Qt for its user interface, via the PyQt bindings.
'frescobaldi' is not a real package: on startup, the absolute 'frescobaldi' directory is added to sys.path and its own path is cleared so all modules and packages inside frescobaldi are available as toplevel modules and packages.
To test features or to experiment, you can run Frescobaldi in an interactive Python shell. It is recommended to open a shell (e.g. by simply running python without arguments, or by using Dreampie or IPython) and then enter:
from frescobaldi.debug import *
This ensures the application starts up and also installs some handlers that print debugging information on certain events. And it imports the most used modules.
There can be one or more mainwindow.MainWindow instances and one or more
document.Document instances (when the last Document is closed, another one is
always constructed). The app module keeps references to those and contains the
Signals emitted when something changes.
Many parts inside Frescobaldi need to store or cache additional information or add features to Documents, MainWindows etc. Instead of clobbering those basic classes with an ever-growing number of unrelated groups of methods, a different approach is chosen: the plugin module.
This keeps all classes small and only have methods that directly apply to themselves and not to other parts of Frescobaldi (separation of concerns).
So e.g. the resultfiles, highlighter or documentinfo modules contain classes for objects that coexist with a Document, and providing their own relevant methods, while keeping a weak reference to the Document.
Exchange of messages is done as much as possible using signals (PyQt signals or from the signals module), or event filters, so adding new features changes as less existing code as possible.
Some important modules:
main: Entry point appinfo: Information about the application, such as the version toplevel: Adds the path of frescobaldi to sys.path, clears path so all modules inside frescobaldi can be imported as toplevel modules and packages app: Central hub with global signals, also keeping references to mainwindow and document instances mainwindow: MainWindow (QMainWindow) document: Document (QTextDocument) view: View (QPlainTextEdit) menu: Here the menubar is constructed (by importing all the relevant modules and adding the actions they define) plugin: A simple way to extend objects without them knowing it metainfo: Stores (optionally) meta information about the document, such as last cursor position, whether to enable auto indent, etc panel: The base class of all dock widgets panelmanager: Add new dock widget tools here symbols: Provides icons of LilyPond-generated SVG files that draw themselves in the default text color.
Some completely generic modules (don't have anything to do with Frescobaldi or LilyPond):
signals: An alternative to Qt signals that allows for connections to have priorities, and objects don't have to be Qt objects cachedproperty: Caches properties that can be asynchronously computed slexer: A Stateful Lexer, used to build regular expression-based parsers hyphenator: Hyphenate text using hyphenation dictionaries node: A list-like type to build tree structures with cursortools: Some useful functions manipulating QTextCursor instances portmidi: Access the PortMidi library in different ways midifile: Load and play MIDI files
A clean pythonic coding style is preferred, with short methods and method names, and small modules and classes that encapsulate functionality in a sensible way. See also PEP8 (http://www.python.org/dev/peps/pep-0008/)
Indent: 4 spaces indent with no tabs
Case: ClassName, module_name, methodname() (or methodName() for classes that inherit from Qt classes). Instance attributes that are not meant to be used from outside an instance are prefixed with an underscore, e.g. self._document.
There is a habit, inspired by Qt, to use setters and getters for such
attributes: obj.setDocument(document) and obj.document().
Names for actions (e.g. file_open) and QSettings keys should always be
lowercase and use underscores where needed.
Write code so that adding or extending functionality later only adds lines, not changes or removes existing lines.
Module imports: one per line. First the Python standard library imports, then PyQt, then the generic Frescobaldi imports and then imports from the current package. The different groups separated by a blank line:
import os # stdlib imports
import sys
from PyQt5.QtCore import ... # PyQt imports
import app # generic Frescobaldi imports
import icons
from . import widget # imports from current package
Avoid platform specific code, but when it is really needed, you can test for them:
if platform.system() == "Linux":
...
elif platform.system() == "Darwin": # macOS
...
elif platform.system() == "Windows":
...
Separate out core functionality from its GUI. Put core functionality in a basic module. For the GUI preferably make a new package/init.py, importing that e.g. from menu.py while constructing the GUI. An example is the documentwatcher base module, it automatically watches open documents on disk, simply by listening to signals sent from app. It sends a documentChanged() signal when something happens, nothing else. The externalchanges package that gets imported from mainwindow.py, starts up the documentwatcher if the user has it enabled.
So the documentwatcher watcher is a module just capable of performing a task, without needing to have logic for accessing the preferences, constructing a particular GUI, etc. It could, like app and many other modules, be used almost unchanged in any other application.
New features that add menu actions can be imported in menu.py, while building the menu. Features that should run in a global background thread can have their toplevel file (/init.py) imported from main.py or mainwindow.py, loading as few as possible on first import.
When preparing a patch or pull request, please add new functionality first. Old functionality that is superseded by the newer functions can be removed later when the new functionality has been tested thoroughly. Change existing files as less as possible. Preferably add new files and packages.
User Interface strings that are meant to be translated should be wrapped in _("Message Text") constructs. See also TRANSLATIONS.md for vital information about how to use the translation mechanism and how to use variables inside messages.
Objects that are longer-lived should be able to retranslate their GUIs. This can be done by adding a method named translateUI(self), in which you set the texts to the user interface objects, and calling app.translateUI() at the end of the constructor. Frescobaldi will call your translateUI() method once and also take care of calling it again when the user changes the UI language in the preferences. You can also do this directly by connecting the method that sets the texts to the app.languageChanged signal.
- Write short, directly and non-technical
- For help pages: each paragraph is one translatable string
- Avoid HTML in texts (but
\includeis OK) - In help pages you can construct HTML using some helper functions
- Avoid hard line breaks (
) in any texts: use short paragraphs instead - Use named format fields: not "page {0} of {1}" but "page {num} of {total}"
- Don't change existing strings just for cosmetics, it breaks translations
Checklist before making a new release:
- Bump the version in
frescobaldi/appinfo.py. - Add the release date in
CHANGELOG.mdandlinux/org.frescobaldi.Frescobaldi.metainfo.xml.in. - Update the list of contributors in
frescobaldi/userguide/credits.md.