python - QApplication'未定义

Question

我从 http://www.pythoncentral.io/pyside-pyqt-tutorial-interactive-widgets-and-layout-containers/ 下载了下面的脚本我收到以下错误消息:NameError: name 'QApplication' is not defined

我添加了脚本的前两行。那没有帮助。我想也许我一定没有安装 qt。但是当我尝试运行 PyQt4-4.10.3-gpl-Py2.7-Qt4.8.5-x32.exe 时，程序告诉我它已经安装。

有人有什么建议吗？

马克

# copied from http://www.pythoncentral.io/pyside-pyqt-tutorial-interactive-widgets-and-layout-containers/
# Every Qt application must have one and only one QApplication object;
# it receives the command line arguments passed to the script, as they
# can be used to customize the application's appearance and behavior

import sys
from PyQt4 import QtGui, QtCore
#import PyQt4.QtGui, PyQt4.QtCore
qt_app = QApplication(sys.argv)

class AbsolutePositioningExample(QWidget):
    ''' An example of PySide absolute positioning; the main window
        inherits from QWidget, a convenient widget for an empty window. '''
    def __init__(self):
        # Initialize the object as a QWidget
        QWidget.__init__(self)

        # We have to set the size of the main window
        # ourselves, since we control the entire layout
        self.setMinimumSize(400, 185)
        self.setWindowTitle('Dynamic Greeter')

        # Create the controls with this object as their parent and set
        # their position individually; each row is a label followed by
        # another control

        # Label for the salutation chooser
        self.salutation_lbl = QLabel('Salutation:', self)
        self.salutation_lbl.move(5, 5) # offset the first control 5px
                                       # from top and left
        self.salutations = ['Ahoy',
                            'Good day',
                            'Hello',
                            'Heyo',
                            'Hi',
                            'Salutations',
                            'Wassup',
                            'Yo']
        # Create and fill the combo box to choose the salutation
        self.salutation = QComboBox(self)
        self.salutation.addItems(self.salutations)

        # Allow 100px for the label and 5px each for borders at the
        # far left, between the label and the combobox, and at the far
        # right
        self.salutation.setMinimumWidth(285)
        # Place it five pixels to the right of the end of the label
        self.salutation.move(110, 5)

        # The label for the recipient control
        self.recipient_lbl = QLabel('Recipient:', self)
        # 5 pixel indent, 25 pixels lower than last pair of widgets
        self.recipient_lbl.move(5, 30)

        # The recipient control is an entry textbox
        self.recipient = QLineEdit(self)
        # Add some ghost text to indicate what sort of thing to enter
        self.recipient.setPlaceholderText(""e.g. 'world' or 'Matey'"")
        # Same width as the salutation
        self.recipient.setMinimumWidth(285)
        # Same indent as salutation but 25 pixels lower
        self.recipient.move(110, 30)

        # The label for the greeting widget
        self.greeting_lbl = QLabel('Greeting:', self)
        # Same indent as the others, but 45 pixels lower so it has
        # physical separation, indicating difference of function
        self.greeting_lbl.move(5, 75)

        # The greeting widget is also a label
        self.greeting = QLabel('', self)
        # Same indent as the other controls
        self.greeting.move(110, 75)

        # The build button is a push button
        self.build_button = QPushButton('&Build Greeting', self)

        # Place it at the bottom right, narrower than
        # the other interactive widgets
        self.build_button.setMinimumWidth(145)
        self.build_button.move(250, 150)

    def run(self):
        # Show the form
        self.show()
        # Run the Qt application
        qt_app.exec_()

# Create an instance of the application window and run it
app = AbsolutePositioningExample()
app.run()

Answer 1

如果您按顺序阅读本教程，您会看到 the previous article该系列中的 显示了您需要在每个片段的开头部分进行分割以使其成为可运行程序的内容。作者这样做显然是为了让相同的代码可以同时用于 PyQt 和 PySide。

因此，如果您使用的是 PyQt4，则需要添加以下内容:

# Allow access to command-line arguments
import sys

# SIP allows us to select the API we wish to use
import sip

# use the more modern PyQt API (not enabled by default in Python 2.x);
# must precede importing any module that provides the API specified
sip.setapi('QDate', 2)
sip.setapi('QDateTime', 2)
sip.setapi('QString', 2)
sip.setapi('QTextStream', 2)
sip.setapi('QTime', 2)
sip.setapi('QUrl', 2)
sip.setapi('QVariant', 2)

# Import all of Qt
from PyQt4.Qt import *

如果是 PySide:

# Allow access to command-line arguments
import sys

# Import the core and GUI elements of Qt
from PySide.QtCore import *
from PySide.QtGui import *

在显示此样板的框下方，有一个很好的、可读的解释，解释了它的含义以及为什么需要这样做。

但是，我建议如果您尝试从教程中学习，请从头开始并继续前进，而不是从中间开始并试图弄清楚一路上您错过了什么。

---

如果您只是执行 from PyQt4 import QtGui, QtCore 而不是从它们导入 *，那么这些模块中的名称是可用的，但只能作为限定名称。也就是说，您必须编写 QtCore.QApplication 而不是 QApplication。

如果您不明白其中的区别，请阅读 Modules在官方 Python 教程或类似的教程中学习导入的工作原理。