什么可能导致python模块导入两次？

Question

据我所知，python模块永远不会被导入两次，即模块中的代码只在第一次被导入时被执行。随后的导入语句只是将该模块添加到导入的范围。

我有一个名为“TiledConvC3D.py”的模块，虽然似乎要多次导入。我使用pdb在该模块的代码顶部打印堆栈。

下面是从第一次执行该模块的堆栈跟踪的末尾：

File "<anonymized>/python_modules/Theano/theano/gof/cmodule.py", line 328, in refresh 
    key = cPickle.load(open(key_pkl, 'rb')) 
File "<anonymized>/ops/TiledConvG3D.py", line 565, in <module> 
    import TiledConvC3D 
File "<anonymized>/ops/TiledConvC3D.py", line 18, in <module> 
    pdb.traceback.print_stack() 

它接着被执行数次。但是，完整的堆栈跟踪它被称为不显示任何来电reload第二次，所以这些执行不应该发生：

File "sup_train_conj_grad.py", line 103, in <module> 
    dataset = Config.get_dataset(dataset_node) 
File "<anonymized>/Config.py", line 279, in get_dataset 
    from datasets import NewWiskott 
File "<anonymized>/datasets/NewWiskott.py", line 16, in <module> 
    normalizer_train = video.ContrastNormalizer3D(sigma, global_per_frame = False, input_is_5d = True) 
File "<anonymized>/util/video.py", line 204, in __init__ 
    self.f = theano.function([input],output) 
File "<anonymized>/python_modules/Theano/theano/compile/function.py", line 105, in function 
    allow_input_downcast=allow_input_downcast) 
File "<anonymized>/python_modules/Theano/theano/compile/pfunc.py", line 270, in pfunc 
    accept_inplace=accept_inplace, name=name) 
File "<anonymized>/python_modules/Theano/theano/compile/function_module.py", line 1105, in orig_function 
    fn = Maker(inputs, outputs, mode, accept_inplace = accept_inplace).create(defaults) 
File "/u/goodfeli/python_modules/Theano/theano/compile/function_module.py", line 982, in create 
    _fn, _i, _o = self.linker.make_thunk(input_storage = input_storage_lists) 
File "<anonymized>/python_modules/Theano/theano/gof/link.py", line 321, in make_thunk 
    output_storage = output_storage)[:3] 
File "<anonymized>/python_modules/Theano/theano/gof/cc.py", line 1178, in make_all 
    output_storage = node_output_storage) 
File "<anonymized>/python_modules/Theano/theano/gof/cc.py", line 774, in make_thunk 
    cthunk, in_storage, out_storage, error_storage = self.__compile__(input_storage, output_storage) 
File "<anonymized>/python_modules/Theano/theano/gof/cc.py", line 723, in __compile__ 
    output_storage) 
File "<anonymized>/python_modules/Theano/theano/gof/cc.py", line 1037, in cthunk_factory 
    module = get_module_cache().module_from_key(key=key, fn=self.compile_cmodule) 
File "<anonymized>/python_modules/Theano/theano/gof/cc.py", line 59, in get_module_cache 
    return cmodule.get_module_cache(config.compiledir) 
File "<anonymized>/python_modules/Theano/theano/gof/cmodule.py", line 576, in get_module_cache 
    _module_cache = ModuleCache(dirname, force_fresh=force_fresh) 
File "<anonymized>/python_modules/Theano/theano/gof/cmodule.py", line 268, in __init__ 
    self.refresh() 
File "<anonymized>/python_modules/Theano/theano/gof/cmodule.py", line 326, in refresh 
    key = cPickle.load(open(key_pkl, 'rb')) 
File "<anonymized>/ops/TiledConvV3D.py", line 504, in <module> 
    import TiledConvG3D 
File "<anonymized>/ops/TiledConvG3D.py", line 565, in <module> 
    import TiledConvC3D 
File "<anonymized>/ops/TiledConvC3D.py", line 22, in <module> 
    pdb.traceback.print_stack() 

此外，我还检查__builtin__.__import__的ID。在我的主要脚本的开头，我进口__builtin__并打印id(__builtin__.__import__)之前做任何其他进口。我也在我的模块里打印了多次导入id(__builtin__.import__)，并且id的值没有改变。

除了调用重载和覆盖__builtin__.__import__，还有其他的机制可以解释我的模块多次加载吗？

Answer 1

如果在路径中找到两次模块，则可以导入Python模块两次。例如，假设你的项目布局，像这样：

• 的src/
  • 包1/
    • spam.py
    • eggs.py

假设你的PYTHONPATH（sys.path）包含src和src/pac kage1：

PYTHONPATH=/path/to/src:/path/to/src/package1 

如果是这样的话，你可以导入相同的模块两次这样的：

from package1 import spam 
import spam 

和Python会认为他们是不同的模块。这是怎么回事？

此外，根据下面的讨论（用于搜索此问题的用户），另一种模块可以导入两次的方式是在第一次导入中途出现异常。例如，如果垃圾邮件导入鸡蛋，但导入鸡蛋会导致模块内的异常，则可以再次导入鸡蛋。