memento_exercise.py

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from io import StringIO
 
from .memento import IMemento, Memento_TextObject
 
 
_mementoUndoList = [] # type: list[IMemento]
 
 
def Memento_SaveForUndo(text : Memento_TextObject, operation : str) -> None:
    memento = text.GetMemento(operation)
    _mementoUndoList.append(memento)
 
 
 
def Memento_Operation_Replace(source : Memento_TextObject, searchPattern : str, replaceText : str) -> None:
    source.SetText = source.Text.replace(searchPattern, replaceText)
 
 
 
def Memento_Operation_Reverse(source : Memento_TextObject) -> None:
    output = StringIO()
    text = source.Text
    textLength = len(text)
    for index in range(0, textLength):
        output.write(text[textLength - 1 - index])
    source.SetText = output.getvalue()
 
 
 
def Memento_Undo(text : Memento_TextObject) -> None:
    if _mementoUndoList:
        lastMemento = _mementoUndoList.pop()
        text.RestoreMemento(lastMemento)
 
        # Show off what we (un)did.
        print("    undoing operation {0:<31}: \"{1}\"".format(lastMemento.Name, text.ToString()))
 
 
 
def Memento_ApplyReplaceOperation(text : Memento_TextObject, searchPattern : str, replaceText : str) -> None:
    operationName = "Replace '{0}' with '{1}'".format(searchPattern, replaceText)
    Memento_SaveForUndo(text, operationName)
    Memento_Operation_Replace(text, searchPattern, replaceText)
    print("    operation {0:<31}: \"{1}\"".format(operationName, text.ToString()))
 
 
 
def Memento_ApplyReverseOperation(text : Memento_TextObject) -> None:
    operationName = "Reverse"
    Memento_SaveForUndo(text, operationName)
    Memento_Operation_Reverse(text)
    print("    operation {0:<31}: \"{1}\"".format(operationName, text.ToString()))
 
 
 
 
# ! [Using Memento in Python]
def Memento_Exercise():
    print()
    print("Memento Exercise")
 
    # Start with a fresh undo list.
    _mementoUndoList.clear()
 
    # The base text object to work from.
    text = Memento_TextObject("This is a line of text on which to experiment.")
 
    print("  Starting text: \"{0}\"".format(text.ToString()))
 
    # Apply four operations to the text.
    Memento_ApplyReplaceOperation(text, "text", "painting")
    Memento_ApplyReplaceOperation(text, "on", "off")
    Memento_ApplyReverseOperation(text)
    Memento_ApplyReplaceOperation(text, "i", "!")
 
    print("  Now perform undo until back to original")
 
    # Now undo the four operations.
    Memento_Undo(text)
    Memento_Undo(text)
    Memento_Undo(text)
    Memento_Undo(text)
 
    print("  Final text   : \"{0}\"".format(text.ToString()))
 
    print("  Done.")
# ! [Using Memento in Python]