问如何使用熊猫将字符串转换为时间戳

EN

   def _to_timestamp(cls, col):
        """
        Convert a column of a dataframe from String to Timestamp if applicable
        :param col:     A Series object representing a column of a dataframe.
        """
        try:
            col = pd.to_datetime(col)
        except ValueError:
            print(
                "Could not convert field to timestamps: {0}".format(col.name)
            )
            return col

        converted = []
        for i in col:
            try:
                converted.append(i.fromisoformat())   <-- PROBLEM IS HERE
            except ValueError:
                converted.append(pd.np.NaN)
            except AttributeError:
                converted.append(pd.np.NaN)


cols =['originDate', 'destenationDate','caseTimestamp']
df[cols] = df[cols].apply(
                lambda x: self._to_timestamp(x)
            )