python - 将参数传递给 __enter__

Question

刚刚学习 with 语句 especially from this article

问题是，我可以将参数传递给 __enter__ 吗？

我有这样的代码:

class clippy_runner:
    def __enter__(self):
        self.engine = ExcelConnection(filename = "clippytest\Test.xlsx")
        self.db = SQLConnection(param_dict = DATASOURCES[STAGE_RELATIONAL])

        self.engine.connect()
        self.db.connect()

        return self

我想将文件名和 param_dict 作为参数传递给 __enter__。这可能吗？

Answer 1

可以，多加一点代码就可以达到效果。

    #!/usr/bin/env python

    class Clippy_Runner( dict ):
        def __init__( self ):
            pass
        def __call__( self, **kwargs ):
            self.update( kwargs )
            return self
        def __enter__( self ):
            return self
        def __exit__( self, exc_type, exc_val, exc_tb ):
            self.clear()

    clippy_runner = Clippy_Runner()

    print clippy_runner.get('verbose')     # Outputs None
    with clippy_runner(verbose=True):
        print clippy_runner.get('verbose') # Outputs True
    print clippy_runner.get('verbose')     # Outputs None