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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 check_naming_conventions(self, ds):
        '''
        Checks the variable names to ensure they are valid CF variable names under CF.

        CF §2.3 Variable, dimension and attribute names should begin with a letter
        and be composed of letters, digits, and underscores.

        :param netCDF4.Dataset ds: An open netCDF dataset
        :rtype: compliance_checker.base.Result
        '''
        ret_val = []
        variable_naming  = TestCtx(BaseCheck.MEDIUM, self.section_titles['2.3'])
        dimension_naming = TestCtx(BaseCheck.MEDIUM, self.section_titles['2.3'])
        attribute_naming = TestCtx(BaseCheck.MEDIUM, self.section_titles['2.3'])

        ignore_attributes = [
            '_FillValue',
            'DODS',
            '_ChunkSizes',
            '_Coordinate',
            '_Unsigned'
        ]

        rname = regex.compile("^[A-Za-z][A-Za-z0-9_]*$")

        for name, variable in ds.variables.items():
            variable_naming.assert_true(rname.match(name) is not None,
                                        "variable {} should begin with a letter and be composed of "
                                        "letters, digits, and underscores".format(name))

            # Keep track of all the attributes, we'll need to check them
            for attr in variable.ncattrs():
                if attr in ignore_attributes:
                    continue
                # Special attributes made by THREDDS
                if attr.startswith('DODS'):
                    continue
                # Ignore model produced attributes
                if attr.startswith('_Coordinate'):
                    continue
                attribute_naming.assert_true(rname.match(attr) is not None,
                                             "attribute {}:{} should begin with a letter and be composed of "
                                             "letters, digits, and underscores".format(name, attr))

        ret_val.append(variable_naming.to_result())

        for dimension in ds.dimensions:
            dimension_naming.assert_true(rname.match(dimension) is not None,
                                         "dimension {} should begin with a latter and be composed of "
                                         "letters, digits, and underscores".format(dimension))
        ret_val.append(dimension_naming.to_result())

        for global_attr in ds.ncattrs():
            if global_attr.startswith('DODS'):
                continue
            attribute_naming.assert_true(rname.match(global_attr) is not None,
                                         "global attribute {} should begin with a letter and be composed of "
                                         "letters, digits, and underscores".format(global_attr))
        ret_val.append(attribute_naming.to_result())

        return ret_val