Return the list of absolute filepaths in the directory.

        Args:
            wildcard: String of tokens separated by "|". Each token represents a pattern.
                If wildcard is not None, we return only those files that match the given shell pattern (uses fnmatch).
                Example:
                  wildcard="*.nc|*.pdf" selects only those files that end with .nc or .pdf

def list_filepaths(self, wildcard=None):
        """
        Return the list of absolute filepaths in the directory.

        Args:
            wildcard: String of tokens separated by "|". Each token represents a pattern.
                If wildcard is not None, we return only those files that match the given shell pattern (uses fnmatch).
                Example:
                  wildcard="*.nc|*.pdf" selects only those files that end with .nc or .pdf
        """
        # Select the files in the directory.
        fnames = [f for f in os.listdir(self.path)]
        filepaths = filter(os.path.isfile, [os.path.join(self.path, f) for f in fnames])

        # Filter using the shell patterns.
        if wildcard is not None:
            filepaths = WildCard(wildcard).filter(filepaths)

        return filepaths