安装pandas、numpy、matplotlib后Python代码报退出码3求助

我编程经验不多，当前开发的项目是通过USB将嵌入式系统的数据传输至Thonny并存储为CSV文件。尝试用matplotlib、pandas、numpy绘图时，发现未安装这些库，用Thonny内置包管理器安装后，运行程序持续出现“Process ended with exit code 3”错误；移除绘图相关代码及导入语句后，程序可正常运行并写入CSV文件。尝试重装库但无法安装至最新稳定版本，附上代码求助：

import serial
import csv
from time import time as current_time
from time import sleep
import pandas as pd
import numpy as np
import matplotlib as plt

ser = serial.Serial()
ser.baudrate = 115200
ser.port = "COM5"
db_list = []
print("Type CTRL + C to exit. (may take 5 seconds)")


ser.open()

start_time = current_time()

for i in range(10):
          
    microbitdata = str(ser.readline())
    
    decibel_level = microbitdata[2:]
    
    decibel_level = decibel_level.replace(" ","")#removes any spaces from the data
    
    decibel_level = decibel_level.replace("'","")#removes an opostrophies 
    
  
    decibel_level = decibel_level.replace("\\r\\n","")# replace \r\n with a blank space 
    
    decibel_level = decibel_level.replace("\\r","") #replace \r with nothing
    
    decibel_level = decibel_level.replace("\\n","") #replace \n with nothing 
    

    sleep(0.1)#break between data being added
    
    elapsed_time = round(current_time() - start_time)
    print("Elapsed time:", elapsed_time,"/db level:", decibel_level)
    sleep(1)  # Pauses the loop for 1 second
    decibel_level = int(decibel_level)
    db_list.append(decibel_level)
    
    safe = decibel_level <= 70
    potential_damage = 71<= decibel_level <= 90
    risk_of_hearing_loss = 91<= decibel_level <=119
    immediate_harm = decibel_level >= 120
        
    
    path = "Sound_level_data.csv"  #naming the file name 
    f = open(path, "a", newline='')#appends at the end of each line 

    writer = csv.writer(f)

    writer.writerow([elapsed_time,decibel_level])


    f.close()

#calc the trendline and plots the graph
csv = pd.read_csv('Sound_level_data.csv')
data = csv[['Time', 'Sound Level']]
x = data['elapsed_time']
y = data['decibel_level']



plt.scatter(x, y)

z = np.polyfit(x, y, 1)
p = np.poly1d(z)
plt.plot(x,p(x),"r--")
plt.xlabel('db Level')
plt.ylabel('Time')

print("The slope is", z[0])
print("The intercept is", z[1])
print("The equation of the line is y="+str(round(z[0],2))+"x+"+str(round(z[1],2)))

plt.savefig("graph.png")
plt.show()

问题排查与解决方法 #

1. 修正matplotlib导入方式 #

原代码中import matplotlib as plt错误，matplotlib的绘图方法在pyplot子模块中，正确导入应为：

import matplotlib.pyplot as plt

2. 解决CSV列名不匹配问题 #

你写入CSV时没有添加表头，但读取时用了不存在的列名Time、Sound Level，后续又调用elapsed_time、decibel_level，会触发KeyError。修改写入逻辑，首次创建文件时添加表头：

import os  # 需要导入os模块

path = "Sound_level_data.csv"
# 首次创建文件时写入表头
if not os.path.exists(path):
    with open(path, "w", newline='') as f:
        writer = csv.writer(f)
        writer.writerow(['elapsed_time', 'decibel_level'])
# 追加数据
with open(path, "a", newline='') as f:
    writer = csv.writer(f)
    writer.writerow([elapsed_time, decibel_level])

读取时使用正确的列名：

# 不要用csv作为变量名，会覆盖内置的csv模块
df = pd.read_csv('Sound_level_data.csv')
x = df['elapsed_time']
y = df['decibel_level']

3. 增加串口数据异常处理 #

串口数据可能存在格式异常，直接转int会报错，添加异常捕获：

try:
    decibel_level = int(decibel_level)
except ValueError:
    print(f"无效数据：{microbitdata}")
    continue  # 跳过无效数据，继续循环

4. 修复绘图标签错误 #

x轴是时间，y轴是分贝值，原代码标签写反了：

plt.xlabel('时间(秒)')
plt.ylabel('分贝值(db)')

5. 解决Thonny库安装问题 #

如果Thonny内置包管理器无法安装最新版，打开Thonny的「工具」→「打开系统shell」，运行以下命令强制升级：

pip install matplotlib pandas numpy --upgrade

修改后的完整代码 #

import serial
import csv
import os
from time import time as current_time
from time import sleep
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt

ser = serial.Serial()
ser.baudrate = 115200
ser.port = "COM5"
db_list = []
print("Type CTRL + C to exit. (may take 5 seconds)")

ser.open()
start_time = current_time()

path = "Sound_level_data.csv"
# 首次创建文件时写入表头
if not os.path.exists(path):
    with open(path, "w", newline='') as f:
        writer = csv.writer(f)
        writer.writerow(['elapsed_time', 'decibel_level'])

for i in range(10):
    microbitdata = str(ser.readline())
    decibel_level = microbitdata[2:]
    
    # 清理数据
    decibel_level = decibel_level.replace(" ","").replace("'","")
    decibel_level = decibel_level.replace("\\r\\n","").replace("\\r","").replace("\\n","")
    
    sleep(0.1)
    elapsed_time = round(current_time() - start_time)
    print("Elapsed time:", elapsed_time,"/db level:", decibel_level)
    
    # 异常处理：跳过无效数据
    try:
        decibel_level = int(decibel_level)
    except ValueError:
        print(f"跳过无效数据：{microbitdata}")
        sleep(1)
        continue
    
    db_list.append(decibel_level)
    
    # 追加数据到CSV
    with open(path, "a", newline='') as f:
        writer = csv.writer(f)
        writer.writerow([elapsed_time, decibel_level])
    
    sleep(1)

# 绘图部分
df = pd.read_csv('Sound_level_data.csv')
x = df['elapsed_time']
y = df['decibel_level']

plt.scatter(x, y)
# 生成趋势线
z = np.polyfit(x, y, 1)
p = np.poly1d(z)
plt.plot(x, p(x), "r--")

plt.xlabel('时间(秒)')
plt.ylabel('分贝值(db)')
print(f"斜率：{z[0]}")
print(f"截距：{z[1]}")
print(f"趋势线方程：y={round(z[0],2)}x+{round(z[1],2)}")

plt.savefig("graph.png")
plt.show()

内容的提问来源于stack exchange，提问作者GavinMC