history: base history mechanisms

There should be a single instance of this class; you can create it as a global, some kind of singleton, or pass it around.

Base history mechanism

exception pyqtcmd.history.ConsistencyError

Thrown when something bad happens (trying to undo with an empty past list for instance).

class pyqtcmd.history.History

Maintains lists of past and future commands as they are done and undone. The changed signal is emitted whenever the history state changes. This class also maintains a pointer to a ‘saved’ state and can tell if its current state is the saved one or not (see is_modified()).

can_redo()

Returns True if there is at least one future command

can_undo()

Returns True if there is at least one past command

check()

This just emits the changed signal; use it when you think UICommand states should be updated, when add_check_signal is not enough.

freeze()

This context manager will wrap calls to Command.(undo|redo|do). You can override it to provide some sort of batch updating/signalling in your own project.

is_modified()

Returns True if the history state is different from what it was when save_point() was last called (or when constructed, or reset with is_new=False).

past()

Return a copy of past Command objects. This may be useful in situation where, for instance, a modal dialog has a ‘local’ history, and you want to encapsulate everything that has been done in this dialog in a single CompositeCommand when the dialog is closed, and add it to the ‘main’ history.

redo()

Redo the latest command that was undone. Throws ConsistencyError if there are no command to redo.

redo_label()

The text for the current redo command, or None

reset(is_new=True)

Resets the history state. This is typically called when a new document has been loaded or created. If is_new is False, the saved state is not reset, so is_modified() will still return True. This is intended for session management, when loading a document that hasn’t actually been saved yet.

run(command)

Run a command and put it in the past. In order to keep things consistent, the future list is deleted.

save_point()

Sets the ‘saved’ state as the current one. Call this after saving a document to disk for instance.

undo()

Undo the latest command that was run. Throws ConsistencyError if there are no commands to undo.

undo_label()

The text for the current undo command, or None

class pyqtcmd.history.HistoryVersion

History version. Internal use only.