Tkinter live matplotlib错误[重复]

Question

我有一个带有实时图形读取串行数据的 GUI，对我的业余技能来说非常好，但是有人可以向我解释如何摆脱这个错误吗？

File "C:\Users\222\Desktop\V25 Live graph.py", line 200, in measure

cnt=cnt+1

UnboundLocalError: local variable 'cnt' referenced before assignment

我尝试的每件事都会弄乱我的整个项目。谢谢大家的建议，代码如下。

import matplotlib
matplotlib.use("TkAgg")
from matplotlib.figure import Figure
import matplotlib.animation as animation
from matplotlib import style
import tkinter as tk
import time
import serial
from tkinter import *
from tkinter import ttk
import numpy  # Import numpy
import pandas as pd
import numpy as np
import sys
import matplotlib.pyplot as plt #import matplotlib library
from drawnow import *


arduinoData = serial.Serial('com15', 115200) #Creating our serial object named arduinoData

plt.ion()                                    #Tell matplotlib you want interactive mode to plot live data
cnt=0
style.use("ggplot")                          #ggplot...dark_background

tempF= []



# Main Tkinter application
class Application(Frame):

            # Init the variables & start measurements
        def __init__(self, master=None):
                Frame.__init__(self, master)
                root.title( "Stylibleue Dashboard")
                root.state('zoomed')       # This makes full screen on a windows machines

                self.grid(row=0, column=0, sticky="nsew")
                self.grid_rowconfigure(0, weight=1)
                self.grid_columnconfigure(0, weight=3)
                self.columnconfigure(1, weight=3)
                self.columnconfigure(2, weight=3)
                self.columnconfigure(3, weight=3)
                self.columnconfigure(4, weight=3)

                self.B11 = StringVar()
                self.B2 = StringVar()

                self.createWidgets()
                self.pack()
                self.measure()


            # Create display elements
        def createWidgets(self):

                self.temperature = Label(self, text="", font=('Verdana', 20)).grid(row=5, column=0,padx=100,pady=200)
                self.temperature = Label(self, text="", font=('Verdana', 20)).grid(row=5, column=1,padx=100)
                self.temperature = Label(self, text="", font=('Verdana', 20)).grid(row=5, column=2,padx=100)
                self.temperature = Label(self, text="", font=('Verdana', 20)).grid(row=5, column=3,padx=100)
                self.temperature = Label(self, text="", font=('Verdana', 20)).grid(row=5, column=4,padx=100)
                self.temperature = Label(self, text="", font=('Verdana', 20)).grid(row=5, column=5,padx=100)


                ttk.Button(self, text='Graph', command=self.makeFig).grid(row=2, column=5, sticky=E, pady=50)



                ttk.Separator(self,orient=HORIZONTAL).grid(row=1, columnspan=6, sticky="ew")


                self.temperature = Label(self, text="Bassin 2 :", font=('Verdana', 20)).grid(row=2, column=0, sticky= W ,columnspan=2)

                self.temperature = Label(self, text="DO :", font=('Verdana', 20)).grid(row=2, column=1, sticky="nsew")

                self.temperature = Label(self, text="TEMP :", font=('Verdana', 20)).grid(row=2, column=3, sticky="nsew")



        def makeFig(self):

            plt.title('My Live Streaming Sensor Data')      #Plot the title
            plt.grid(True)                                  #Turn the grid on
            plt.ylabel('Temp F')                            #Set ylabels
            plt.plot(tempF, label='Degrees F')              #plot the temperature
            plt.legend(loc='upper left')                    #plot the legend




    # Read the incoming serial data and display it
        def measure(self):

                if(arduinoData.inWaiting()>0):

                        data = arduinoData.readline()

                        data =str(data,'utf-8')                         #removes the surrounding rubbish

                        self.B11.set(str(data))
                        self.temperature = Label(self, textvariable=self.B11, font=('Verdana', 20)).grid(row=2, column=4, sticky="nsew")

                        self.B2.set(str(data))
                        self.temperature = Label(self, textvariable=self.B2, font=('Verdana', 20)).grid(row=2, column=2, sticky="nsew")

                        tempF.append(data)                              #Build our tempF array by appending temp readings

                        print(data)                 

        # Wait 1 second between each measurement
                self.after(1000,self.measure)

                arduinoData.flushOutput()
                arduinoData.flushInput()

                drawnow(self.makeFig)                           #Call drawnow to update our live graph
                plt.pause(.000001)                              #Pause Briefly. Important to keep drawnow from crashing
                cnt=cnt+1
                if(cnt>5000):                                   #If you have 50 or more points, delete the first one from the array
                     tempF.pop(0)                               #This allows us to just see the last 50 data points


# Create and run the GUI
root = Tk()
app = Application(master=root)
app.mainloop()

Answer 1

您的 python 解释器正在本地范围内寻找 cnt 变量，这是因为对其进行了分配。考虑这个例子，它显示了相同的行为：

c = 0
def foo():
    c=c+1
foo()
Traceback (most recent call last):
  File "C:\...\miniconda3\envs\py36\lib\site-packages\IPython\core\interactiveshell.py", line 2963, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-4-c19b6d9633cf>", line 1, in <module>
    foo()
  File "<ipython-input-3-454c342b701e>", line 2, in foo
    c=c+1
UnboundLocalError: local variable 'c' referenced before assignment

现在如果你改写

c=0
def foo():
    d=c+1
foo()

不会有错误。为了说服您的解释器使用全局变量而不是在本地范围内搜索它，请使用 global 关键字：

c=0
def foo():
    global c
    c = c+1
foo()
print(c)
Out[11]: 1