python函数的写法

如下图，这些函数是这么写的，没有函数体，第一次见，这是什么写法？
这是pyqt5的源码

这不是源码，这类似java里的jar包一样的，能看到函数声明，但是看不到函数定义

• 你可以参考下这个问题的回答, 看看是否对你有帮助, 链接: https://ask.csdn.net/questions/7809101
• 这篇博客也不错, 你可以看下PyQt5 环境搭建+配置+怎样运行生成的.py程序
• 除此之外, 这篇博客: Python 截图 快捷键截图，一个基于PyQt5的截图，简易截图，自由截图 --pyqt5 入门中的 以下是全部代码 部分也许能够解决你的问题, 你可以仔细阅读以下内容或跳转源博客中阅读:
  

• import sys
  import keyboard
  from PyQt5.QtWidgets import QApplication, QWidget
  from PyQt5.QtCore import Qt, qAbs, QRect
  from PyQt5.QtGui import QPen, QPainter, QColor, QGuiApplication
  
  class CaptureScreen(QWidget):
      # 初始化变量
      beginPosition = None
      endPosition = None
      fullScreenImage = None
      captureImage = None
      isMousePressLeft = None
      painter = QPainter()
  
      def __init__(self):
          super(QWidget, self).__init__()
          self.initWindow()   # 初始化窗口
          self.captureFullScreen()    # 获取全屏
  
      def initWindow(self):
          self.setMouseTracking(True)     # 鼠标追踪
          self.setCursor(Qt.CrossCursor)  # 设置光标
          self.setWindowFlag(Qt.FramelessWindowHint)  # 窗口无边框
          self.setWindowState(Qt.WindowFullScreen)    # 窗口全屏
  
      def captureFullScreen(self):
          self.fullScreenImage = QGuiApplication.primaryScreen().grabWindow(QApplication.desktop().winId())
  
      def mousePressEvent(self, event):
          if event.button() == Qt.LeftButton:
              self.beginPosition = event.pos()
              self.isMousePressLeft = True
          if event.button() == Qt.RightButton:
              # 如果选取了图片,则按一次右键开始重新截图
              if self.captureImage is not None:
                  self.captureImage = None
                  self.paintBackgroundImage()
                  self.update()
              else:
                  self.close()
  
      def mouseMoveEvent(self, event):
          if self.isMousePressLeft is True:
              self.endPosition = event.pos()
              self.update()
  
      def mouseReleaseEvent(self, event):
          self.endPosition = event.pos()
          self.isMousePressLeft = False
  
      def mouseDoubleClickEvent(self, event):
          if self.captureImage is not None:
              self.saveImage()
              self.close()
  
      def keyPressEvent(self, event):
          if event.key() == Qt.Key_Escape:
              self.close()
          if event.key() == Qt.Key_Enter or event.key() == Qt.Key_Return:
              if self.captureImage is not None:
                  self.saveImage()
                  self.close()
  
      def paintBackgroundImage(self):
          shadowColor = QColor(0, 0, 0, 100)  # 黑色半透明
          self.painter.drawPixmap(0, 0, self.fullScreenImage)
          self.painter.fillRect(self.fullScreenImage.rect(), shadowColor)     # 填充矩形阴影
  
      def paintEvent(self, event):
          self.painter.begin(self)    # 开始重绘
          self.paintBackgroundImage()
          penColor = QColor(30, 144, 245)     # 画笔颜色
          self.painter.setPen(QPen(penColor, 1, Qt.SolidLine, Qt.RoundCap))    # 设置画笔,蓝色,1px大小,实线,圆形笔帽
          if self.isMousePressLeft is True:
              pickRect = self.getRectangle(self.beginPosition, self.endPosition)   # 获得要截图的矩形框
              self.captureImage = self.fullScreenImage.copy(pickRect)         # 捕获截图矩形框内的图片
              self.painter.drawPixmap(pickRect.topLeft(), self.captureImage)  # 填充截图的图片
              self.painter.drawRect(pickRect)     # 画矩形边框
          self.painter.end()  # 结束重绘
  
      def getRectangle(self, beginPoint, endPoint):
          pickRectWidth = int(qAbs(beginPoint.x() - endPoint.x()))
          pickRectHeight = int(qAbs(beginPoint.y() - endPoint.y()))
          pickRectTop = beginPoint.x() if beginPoint.x() < endPoint.x() else endPoint.x()
          pickRectLeft = beginPoint.y() if beginPoint.y() < endPoint.y() else endPoint.y()
          pickRect = QRect(pickRectTop, pickRectLeft, pickRectWidth, pickRectHeight)
          # 避免高度宽度为0时候报错
          if pickRectWidth == 0:
              pickRect.setWidth(2)
          if pickRectHeight == 0:
              pickRect.setHeight(2)
  
          return pickRect
  
      def saveImage(self):
          self.captureImage.save('picture.png', quality=95)   # 保存图片到当前文件夹中
  
  if __name__ == "__main__":
      keyboard.wait(hotkey='f4')  # 按F4开始截图
      app = QApplication(sys.argv)
      windows = CaptureScreen()
      windows.show()
      sys.exit(app.exec_())
  

  
  
  

这个应该只是提纲一类的东西，源代码不可能这么写