10.2 控制模块被全部导入的内容

问题¶

You want precise control over the symbols that are exported from a module or package when a user uses the from module import * statement.

解决方案¶

Define a variable __all__ in your module that explicitly lists the exported names. For example:

# somemodule.py
def spam():
    pass

def grok():
    pass

blah = 42
# Only export 'spam' and 'grok'
__all__ = ['spam', 'grok']

讨论¶

Although the use of from module import * is strongly discouraged, it still sees frequent use in modules that define a large number of names. If you don’t do anything, this form of import will export all names that don’t start with an underscore. On the other hand, if __all__ is defined, then only the names explicitly listed will be exported.

If you define __all__ as an empty list, then nothing will be exported. An AttributeEr ror is raised on import if __all__ contains undefined names.