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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def df(self):
 """ Makes a pandas DataFrame containing Curve data for all the wells in the Project. The DataFrame has a dual index of well UWI and curve Depths. Requires `pandas`. Args: No arguments. Returns: `pandas.DataFrame`. """

        import pandas as pd
        return pd.concat([w.df(uwi=True) for w in self])