创建 Python Facade 包

Question

I'm not sure how to describe this, but is there a way to create an façade package that handles multiple versions of a internal package?

Consider:

Foo/
    __init__.py
    A/
       Bar/
       __init__.py
       etc.
    B/
       Bar/
       __init__.py
       etc.
    C/
       Bar/    
       __init__.py
       etc.

Inside Package's __init__.py I have python logic to append the sys.path to point to one of the Bar packages depending on the runtime configuration. This leaves me using two python import statements.

import Foo
import Bar

Can I reduce that to one import statement and treat Foo as a façade for the correct version of Bar. The only was I have found is based on this post . In foo.py's __init__.py :

for attr in dir(bar):
    globals()[attr] = getattr(bar, attr) 

Answer 1

I would recommend against modifying system.path since that can have implications for unrelated code.

You can get this behavior by using sys.modules . When a module is imported, it is registered in the sys.modules dictionary. You can accomplish this simply by setting the entry for the proxy module when it is imported.

implementation.py:

def method():
    print "implemented method"

proxy.py:

if __name__ != '__main__':
    import sys
    import implementation
    sys.modules[__name__] = implementation

main.py:

if __name__ == '__main__':
    import proxy
    proxy.method()

output:

$ python main.py 
implemented method