Python线程未等待问题：或与面向对象设计及传参错误有关

在基于DearPyGUI开发GUI界面时，需加载3GB级大文件，因此采用线程优化长IO操作。在类实例方法中启动线程调用同类方法更新对象属性时，出现两个异常：

• 线程抛出TypeError（方法参数数量不匹配）
• 主线程执行thread.join()后，调用属性的getVersion()方法触发AttributeError（属性为None）

线程未完成IO操作就终止，主线程未等待其执行完毕。

原代码 #

class IOClass:
    __init__(self):
        self.fileObj = None
    def loadFile(self, fileName):
        thread = threading.Thread(target=self.threadMethod, args=fileName)
        thread.start()
        #Load GUI wait-screen
        thread.join()
        #anything else..EXCEPTION THROWN HERE
        print(" ".join(["Version:", self.fileObj.getVersion()]))
    def threadMethod(self, fileName):
        print(" ".join(["Loading filename", fileName]))
        #expensive-basic Python IO operation here
        self.fileObj = ...python IO operation here
class GUIClass:
    __init__(self):
        pass
    def startMethod(self):
        #this is called by __main__
        ioClass = IOClass()
        ioClass.loadFile("filename.txt")

报错信息 #

Exception in thread Thread-1 (loadFile):
Traceback (most recent call last):
  File "/home/anthony/anaconda3/envs/CPRD-software/lib/python3.10/threading.py", line 1009, in _bootstrap_inner
    self.run()
  File "/home/anthony/anaconda3/envs/CPRD-software/lib/python3.10/threading.py", line 946, in run
    self._target(*self._args, **self._kwargs)
TypeError: AnalysisController.loadFile() takes 2 positional arguments but 25 were given
Traceback (most recent call last):
  File "/home/anthony/CPRD-software/GUI/Controllers/AnalysisController.py", line 117, in loadStudySpace
    print(" ".join(["Version:", self.fileObj.getVersion()]))
AttributeError: 'NoneType' object has no attribute 'getVersion'

问题根源与解决方案 #

问题分析 #

创建Thread对象时，args参数需传入元组，但原代码直接传入字符串fileName。字符串会被Python视为可迭代对象，拆分为单个字符作为多个参数传递给threadMethod，导致方法参数数量不匹配，触发TypeError。线程因异常终止后，self.fileObj未被赋值，主线程访问时自然抛出AttributeError。

修正代码 #

只需将args参数改为元组格式（注意末尾的逗号，确保是元组而非单个元素），同时补充原代码遗漏的def关键字：

class IOClass:
    def __init__(self):
        self.fileObj = None
    def loadFile(self, fileName):
        # 修正args为元组格式
        thread = threading.Thread(target=self.threadMethod, args=(fileName,))
        thread.start()
        #Load GUI wait-screen
        thread.join()
        print(" ".join(["Version:", self.fileObj.getVersion()]))
    def threadMethod(self, fileName):
        print(" ".join(["Loading filename", fileName]))
        #expensive-basic Python IO operation here
        self.fileObj = ...python IO operation here
class GUIClass:
    def __init__(self):
        pass
    def startMethod(self):
        #this is called by __main__
        ioClass = IOClass()
        ioClass.loadFile("filename.txt")

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