无法从另一个python .py文件运行进程

Question

我正在创建一个类，并且在初始化它时，我正在调用（多进程）它的函数。当我从相同的.py文件创建此类时，一切正常。但是，当我从另一个.py文件初始化此类时 - 它会失败并引发错误...为什么？

MyDummyClass.py：

import multiprocessing 
class MyDummyClass:    
    def __init__(self):   

     print("I am in '__init__()'") 

     if __name__ == 'MyDummyClass': 

      p = multiprocessing.Process(target=self.foo()) 
      p.start() 


    def foo(self): 
     print("Hello from foo()") 

example.py：

from MyDummyClass import MyDummyClass 
dummy = MyDummyClass() 

当我运行example.py，我收到此错误：

I am in '__init__()' 
Hello from foo() 
I am in '__init__()' 
Hello from foo() 

Traceback (most recent call last): 
    File "<string>", line 1, in <module> 
    File "C:\Python\lib\multiprocessing\spawn.py", line 105, in spawn_main 
    exitcode = _main(fd) 
    File "C:\Python\lib\multiprocessing\spawn.py", line 114, in _main 
    prepare(preparation_data) 
    File "C:\Python\lib\multiprocessing\spawn.py", line 225, in prepare 
    _fixup_main_from_path(data['init_main_from_path']) 
    File "C:\Python\lib\multiprocessing\spawn.py", line 277, in _fixup_main_from_path 
    run_name="__mp_main__") 
    File "C:\Python\lib\runpy.py", line 263, in run_path 
    pkg_name=pkg_name, script_name=fname) 
    File "C:\Python\lib\runpy.py", line 96, in _run_module_code 
    mod_name, mod_spec, pkg_name, script_name) 
    File "C:\Python\lib\runpy.py", line 85, in _run_code 
    exec(code, run_globals) 
    File "E:\Dropbox\Docs\Business\_NZTrackAlerts\Website\Current dev\NZtracker\cgi-bin\example1.py", line 2, in <module> 
    dummy = MyDummyClass() 
    File "...path to my file...\MyDummyClass.py", line 13, in __init__ 
    p.start() 
    File "C:\Python\lib\multiprocessing\process.py", line 105, in start 
    self._popen = self._Popen(self) 
    File "C:\Python\lib\multiprocessing\context.py", line 223, in _Popen 
    return _default_context.get_context().Process._Popen(process_obj) 
    File "C:\Python\lib\multiprocessing\context.py", line 322, in _Popen 
    return Popen(process_obj) 
    File "C:\Python\lib\multiprocessing\popen_spawn_win32.py", line 33, in __init__ 
    prep_data = spawn.get_preparation_data(process_obj._name) 
    File "C:\Python\lib\multiprocessing\spawn.py", line 143, in get_preparation_data 
    _check_not_importing_main() 
    File "C:\Python\lib\multiprocessing\spawn.py", line 136, in _check_not_importing_main 
    is not going to be frozen to produce an executable.''') 
RuntimeError: 
     An attempt has been made to start a new process before the 
     current process has finished its bootstrapping phase. 

     This probably means that you are not using fork to start your 
     child processes and you have forgotten to use the proper idiom 
     in the main module: 

      if __name__ == '__main__': 
       freeze_support() 
       ... 

     The "freeze_support()" line can be omitted if the program 
     is not going to be frozen to produce an executable. 

我不明白（而不是来回m其他职位）如何解决它。

非常感谢您的帮助！

Answer 1

这与python实际执行脚本的方式有关。抛出的错误基本上说，当python还没有准备好时，你正试图开始一个新的进程。这是因为你在主脚本中调用了dummy = MyDummyClass()而没有给python一个完全初始化的机会。如果你不是有example.py这样的：

from MyDummyClass import MyDummyClass 
if __name__ == "__main__": 
    dummy = MyDummyClass() 

这将产生所需输出：

C:\Python Scripts>python example.py 
I am in '__init__()' 
Hello from foo() 

的if __name__ == "__main__"块告诉蟒蛇“只有当脚本正在运行为主脚本执行这个（即python example.py），这将强制python在运行该块之前正确初始化所有内容。

道歉，如果此答案没有足够的描述python后端发生了什么，因为它正在做初始化，我自己也不知道一吨:)