为什么try循环不能从Matplotlib mathtext捕获ParseException？

qeeaahzv 于 2023-03-30 发布在其他

关注(0)|答案(1)|浏览(118)

wxPython 4.2.0 x Matplotlib 3.6.0
我正在开发一个GUI，用户可以在textctrl中编写一个图形标题，然后将此标题设置在一个图形上并显示该图形。
我现在的问题是，我不明白为什么try循环不能捕捉到当标题是错误的数学文本时发生的ParseException。
我的问题的简化代码是：

import matplotlib.pyplot as plt
from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg as FigureCanvas
import wx

class MyApp(wx.App):
    def OnInit(self):
        self.frame = MainFrame(parent=None, title="Test")
        self.frame.Show()
        return True

class MainFrame(wx.Frame):
    def __init__(self, parent, title):
        wx.Frame.__init__(self, None, -1, title=title)
        fig = plt.figure()
        fig.suptitle('$$')
        try:
            self.canvas = FigureCanvas(self, 0, fig)
        except:
            self.canvas = FigureCanvas(self, 0, plt.figure())
        plt.close()
        hbox = wx.BoxSizer(wx.HORIZONTAL)
        hbox.Add(self.canvas)
        self.SetSizer(hbox)

if __name__ == "__main__":
    app = MyApp()
    app.MainLoop()

出现以下错误：

Traceback (most recent call last):
...
    raise exc.with_traceback(None)
pyparsing.exceptions.ParseException: Expected end of text, found '$'  (at char 0), (line:1, col:1)

The above exception was the direct cause of the following exception:
...
...
ValueError:
$$
^
Expected end of text, found '$'  (at char 0), (line:1, col:1)

try循环应该能捕捉到这个，对吗？
例如，我使用了set_parse_math（False）方法，这样错误就不会发生，但是，我想知道这段代码有什么问题。

matplotlib

来源：https://stackoverflow.com/questions/75790106/why-can-the-try-loop-not-catch-a-parseexception-from-matplotlib-mathtext

1条答案

按热度按时间

ccgok5k51#

我根据以下讨论找到了解决方案：
Validate MathText string at runtime
下面是我的工作代码：

import matplotlib as mpl
import matplotlib.pyplot as plt
from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg as FigureCanvas
import wx

mpl.use('Agg') # important

class MyApp(wx.App):
    def OnInit(self):
        self.frame = MainFrame(parent=None, title="Test")
        self.frame.Show()
        return True

class MainFrame(wx.Frame):
    def __init__(self, parent, title):
        wx.Frame.__init__(self, None, -1, title=title)
        self.Maximize()
        self.fig = plt.figure()
        self.fig.add_subplot()
        self.canvas = FigureCanvas(self, 0, self.fig)
        hbox = wx.BoxSizer(wx.HORIZONTAL)
        hbox.Add(self.canvas)
        self.txtctrl = wx.TextCtrl(self)
        self.txtctrl.Bind(wx.EVT_TEXT, self.on_text)
        hbox.Add(self.txtctrl)
        self.SetSizer(hbox)
        plt.close()

    def verif_fig_text(self):
        self.Freeze()
        self.canvas.figure = plt.figure()
        ax = self.canvas.figure.add_subplot() # needed to insert x_label
        self.canvas.draw() # needed to get self.canvas.renderer attr
        valid_txt = True
        try:
            txt = ax.set_xlabel(self.txtctrl.GetValue()) 
            # insert x_label is the only mean to verif correct math text
            txt._get_layout(self.canvas.renderer)
            # indeed _get_layout() doesnt work with lot of stuff - found on Valid Mathtext string at runtime StackOverflow
        except:
            valid_txt = False # can't do much here, by adding anything else, the exception occurs outside the try loop
        plt.close()
        self.Thaw()
        return valid_txt
    
    def on_text(self, event):
        if self.verif_fig_text():
            self.fig.suptitle(self.txtctrl.GetValue())
        else:
            self.fig.suptitle('Wrong math text')
        self.canvas.figure = self.fig
        self.canvas.draw()
        plt.close()


if __name__ == "__main__":
    app = MyApp()
    app.MainLoop()

事实上，当有一个wx.EVT_TEXT时，我将一个新的（临时的）图设置为self.canvas。在这个图上，我添加一个子图，然后用textctrl值设置xlabel值，我使用_get_layout（）方法检查文本是否是正确的数学文本，如果是，我将此文本设置为初始图的标题，并将其设置回self.canvas.draw（）之前的self.canvas.figure

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为什么try循环不能从Matplotlib mathtext捕获ParseException？

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