python - 理解一段python代码

Question

我的问题是指问题How to capture output of Python's interpreter and show in a Text widget?的已接受答案。它显示了如何将标准输出重定向到 QTextEdit。

作者 Ferdinand Beyer 定义了一个 EmittingStream 类:

from PyQt4 import QtCore

class EmittingStream(QtCore.QObject):

    textWritten = QtCore.pyqtSignal(str)

    def write(self, text):
        self.textWritten.emit(str(text))

他这样使用这个类:

# Within your main window class...

def __init__(self, parent=None, **kwargs):
    # ...

    # Install the custom output stream
    sys.stdout = EmittingStream(textWritten=self.normalOutputWritten)

def __del__(self):
    # Restore sys.stdout
    sys.stdout = sys.__stdout__

def normalOutputWritten(self, text):
    """Append text to the QTextEdit."""
    # Maybe QTextEdit.append() works as well, but this is how I do it:
    cursor = self.textEdit.textCursor()
    cursor.movePosition(QtGui.QTextCursor.End)
    cursor.insertText(text)
    self.textEdit.setTextCursor(cursor)
    self.textEdit.ensureCursorVisible()

我不明白实例化 EmittingStream 类的行。看起来关键字参数 textWritten=self.normalOutputWritten 将 textWritten-signal 连接到 normalOutputWritten-slot，但我不明白为什么这行得通。

Answer 1

这个特征是documented here :

It is also possible to connect signals by passing a slot as a keyword argument corresponding to the name of the signal when creating an object, or using the pyqtConfigure() method of QObject. For example the following three fragments are equivalent:

act = QtGui.QAction("Action", self)
act.triggered.connect(self.on_triggered)

act = QtGui.QAction("Action", self, triggered=self.on_triggered)

act = QtGui.QAction("Action", self)
act.pyqtConfigure(triggered=self.on_triggered)