自定义Matplotlib Figure类中rcParams无法生效的解决咨询

我尝试基于matplotlib.figure.Figure编写自定义图形类，以自动应用正确格式，但rcParams无论放在代码的哪个位置（甚至类定义之前）都无法生效。当前代码如下：

import matplotlib
from matplotlib.axes import Axes
from matplotlib.figure import Figure
from matplotlib.backends.backend_qtagg import FigureCanvasQTAgg as Canvas

class CustomFigure(Figure):
    def __init__(self, figsize: tuple, layout: str):
        super().__init__(figsize=figsize, layout=layout)
        self.canvas = Canvas(self)
        matplotlib.use("QtAgg")
        self.set_common_params()
        
        
    def generate_axes(self, num_axes: int, layout: tuple = None) -> Axes:
        if layout is None:
            layout = (1, num_axes)
        return self.subplots(*layout)
    
        
    def set_common_params(self):
        matplotlib.rcParams["figure.titlesize"] = 45
        matplotlib.rcParams["axes.titlesize"]   = 13
        matplotlib.rcParams["axes.labelsize"]   = 12
        matplotlib.rcParams["axes.linewidth"]   = 1.5
        matplotlib.rcParams["xtick.labelsize"]  = 11
        matplotlib.rcParams["ytick.labelsize"]  = 11
        
    
    @staticmethod
    def set_labels(ax: Axes, xlabel: str, ylabel: str, title: str = None):
        ax.set_xlabel(xlabel)
        ax.set_ylabel(ylabel)
        if title is not None:
            ax.set_title(title)
            
    
    def generate_pdf(self, filename: str):
        self.savefig(f"{filename}.pdf")
        
        

if __name__ == "__main__":
    import sys
    from PySide6.QtWidgets import QApplication, QMainWindow
    app = QApplication(sys.argv)
    win = QMainWindow()
    fig = CustomFigure((5,5), "tight")
    fig.set_labels(fig.generate_axes(1), "X", "Y", "Title")
    win.setCentralWidget(fig.canvas)
    win.show()
    sys.exit(app.exec())

解决方案 #

1. 提前设置Matplotlib后端 #

matplotlib.use("QtAgg")必须在任何Matplotlib组件初始化之前调用，不能放在CustomFigure的__init__方法中。将其移到文件最开头，导入Matplotlib后立即执行：

import matplotlib
matplotlib.use("QtAgg")  # 移到此处
from matplotlib.axes import Axes
from matplotlib.figure import Figure
from matplotlib.backends.backend_qtagg import FigureCanvasQTAgg as Canvas

2. 在Figure初始化前设置rcParams #

rcParams是全局配置，仅对之后创建的Matplotlib对象生效。当前代码中set_common_params在super().__init__之后调用，此时Figure已经创建，配置无法应用到当前实例。修改__init__方法，先设置rcParams再初始化父类：

def __init__(self, figsize: tuple, layout: str):
    self.set_common_params()  # 先设置全局配置
    super().__init__(figsize=figsize, layout=layout)  # 再初始化Figure
    self.canvas = Canvas(self)

修改后的完整代码 #

import matplotlib
matplotlib.use("QtAgg")
from matplotlib.axes import Axes
from matplotlib.figure import Figure
from matplotlib.backends.backend_qtagg import FigureCanvasQTAgg as Canvas

class CustomFigure(Figure):
    def __init__(self, figsize: tuple, layout: str):
        self.set_common_params()
        super().__init__(figsize=figsize, layout=layout)
        self.canvas = Canvas(self)
        
        
    def generate_axes(self, num_axes: int, layout: tuple = None) -> Axes:
        if layout is None:
            layout = (1, num_axes)
        return self.subplots(*layout)
    
        
    def set_common_params(self):
        matplotlib.rcParams["figure.titlesize"] = 45
        matplotlib.rcParams["axes.titlesize"]   = 13
        matplotlib.rcParams["axes.labelsize"]   = 12
        matplotlib.rcParams["axes.linewidth"]   = 1.5
        matplotlib.rcParams["xtick.labelsize"]  = 11
        matplotlib.rcParams["ytick.labelsize"]  = 11
        
    
    @staticmethod
    def set_labels(ax: Axes, xlabel: str, ylabel: str, title: str = None):
        ax.set_xlabel(xlabel)
        ax.set_ylabel(ylabel)
        if title is not None:
            ax.set_title(title)
            
    
    def generate_pdf(self, filename: str):
        self.savefig(f"{filename}.pdf")
        
        

if __name__ == "__main__":
    import sys
    from PySide6.QtWidgets import QApplication, QMainWindow
    app = QApplication(sys.argv)
    win = QMainWindow()
    fig = CustomFigure((5,5), "tight")
    ax = fig.generate_axes(1)
    fig.set_labels(ax, "X", "Y", "Title")
    win.setCentralWidget(fig.canvas)
    win.show()
    sys.exit(app.exec())

额外优化 #

原测试代码中fig.set_labels(fig.generate_axes(1), ...)会重复创建Axes（generate_axes每次调用都会生成新的子图），建议先保存Axes实例再调用set_labels，避免不必要的资源消耗（如上述修改后的代码所示）。

内容的提问来源于stack exchange，提问作者ohshitgorillas