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• 分解

matplotlib：一个绘图用的Python模块

backends：matplotlib中的一个模块，后端。

backend_qt5agg：backends里面的一个模块，里面有两个类：FigureCanvasQTAgg 和_BackendQT5Agg

FigureCanvasQTagg：backend_qt5agg里的一个类

• FigureCanvasQTagg应用

matplotlib绘制的图可以应用在PyQt5应用里面，下面三个import都需要：

from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvasfrom matplotlib.figure import Figureimport matplotlib.pyplot as plt

**matplotlib.backends.backend_qt5agg用来连接Matplotlib和PyQt5。**backend_qt5agg.py的原文如下：

"""Render to qt from agg."""import ctypesfrom matplotlib.transforms import Bboxfrom .. import cbookfrom .backend_agg import FigureCanvasAggfrom .backend_qt5 import (    QtCore, QtGui, QtWidgets, _BackendQT5, FigureCanvasQT, FigureManagerQT,    NavigationToolbar2QT, backend_version)from .qt_compat import QT_APIclass FigureCanvasQTAgg(FigureCanvasAgg, FigureCanvasQT):    def __init__(self, figure):        # Must pass 'figure' as kwarg to Qt base class.        super().__init__(figure=figure)    def paintEvent(self, event):        """Copy the image from the Agg canvas to the qt.drawable.        In Qt, all drawing should be done inside of here when a widget is        shown onscreen.        """        if self._update_dpi():            # The dpi update triggered its own paintEvent.            return        self._draw_idle()  # Only does something if a draw is pending.        # If the canvas does not have a renderer, then give up and wait for        # FigureCanvasAgg.draw(self) to be called.        if not hasattr(self, 'renderer'):            return        painter = QtGui.QPainter(self)        rect = event.rect()        left = rect.left()        top = rect.top()        width = rect.width()        height = rect.height()        # See documentation of QRect: bottom() and right() are off by 1, so use        # left() + width() and top() + height().        bbox = Bbox(            [[left, self.renderer.height - (top + height * self._dpi_ratio)],             [left + width * self._dpi_ratio, self.renderer.height - top]])        reg = self.copy_from_bbox(bbox)        buf = cbook._unmultiplied_rgba8888_to_premultiplied_argb32(            memoryview(reg))        # clear the widget canvas        painter.eraseRect(rect)        qimage = QtGui.QImage(buf, buf.shape[1], buf.shape[0],                              QtGui.QImage.Format_ARGB32_Premultiplied)        if hasattr(qimage, 'setDevicePixelRatio'):            # Not available on Qt4 or some older Qt5.            qimage.setDevicePixelRatio(self._dpi_ratio)        origin = QtCore.QPoint(left, top)        painter.drawImage(origin / self._dpi_ratio, qimage)        # Adjust the buf reference count to work around a memory        # leak bug in QImage under PySide on Python 3.        if QT_API in ('PySide', 'PySide2'):            ctypes.c_long.from_address(id(buf)).value = 1        self._draw_rect_callback(painter)        painter.end()    def blit(self, bbox=None):        """Blit the region in bbox.        """        # If bbox is None, blit the entire canvas. Otherwise        # blit only the area defined by the bbox.        if bbox is None and self.figure:            bbox = self.figure.bbox        # repaint uses logical pixels, not physical pixels like the renderer.        l, b, w, h = [pt / self._dpi_ratio for pt in bbox.bounds]        t = b + h        self.repaint(l, self.renderer.height / self._dpi_ratio - t, w, h)    def print_figure(self, *args, **kwargs):        super().print_figure(*args, **kwargs)        self.draw()@_BackendQT5.exportclass _BackendQT5Agg(_BackendQT5):    FigureCanvas = FigureCanvasQTAgg

• Reference