假设我们有一个包含两个模块foo和bar的软件包.里面的foo我们需要能够访问吧.
因为我们还在开发它,所以mypackage不在sys.path中.
我们希望能够：
> import mypackage.foo
>运行foo.py作为脚本,并从__main__部分执行示例使用或测试.
>使用Python 2.5
为了确保在所有这些情况下都能正常工作,我们必须在foo.py中进行导入.
- # mypackage/__init__.py
- ...
- # mypackage/foo/__init__.py
- ...
- # mypackage/bar.py
- def doBar()
- print("doBar")
- # mypackage/foo/foo.py
- import bar # fails with module not found
- import .bar #fails due to ValueError: Attempted relative import in non-package
- def doFoo():
- print(doBar())
- if __name__ == '__main__':
- doFoo()
解决方法
Relative imports use a module’s
__name__attribute to determine that module’s position in the package hierarchy. If the module’s name does not contain any package information (e.g. it is set to'__main__') then relative imports are resolved as if the module were a top level module,regardless of where the module is actually located on the file system.
当您将foo.py作为脚本运行时,该模块的__name__是“__main__”,因此您不能进行相对导入.即使mypackage在sys.path上也是如此.基本上,如果导入了该模块,则只能从模块进行相对导入.
以下是解决这个问题的几个选择：
1)在foo.py中,检查是否__name__ ==’__main__’,并有条件地将mypackage添加到sys.path中：
- if __name__ == '__main__':
- import os,sys
- # get an absolute path to the directory that contains mypackage
- foo_dir = os.path.dirname(os.path.join(os.getcwd(),__file__))
- sys.path.append(os.path.normpath(os.path.join(foo_dir,'..','..')))
- from mypackage import bar
- else:
- from .. import bar
2)始终使用mypackage导入栏导入栏,并执行foo.py,使得mypackage可以自动显示：
- $cd <path containing mypackage>
- $python -m mypackage.foo.foo