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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 compile_mof_string(self, mof_str, namespace=None, search_paths=None, verbose=None):
 """ Compile the MOF definitions in the specified string and add the resulting CIM objects to the specified CIM namespace of the mock repository. If the namespace does not exist, :exc:`~pywbem.CIMError` with status CIM_ERR_INVALID_NAMESPACE is raised. This method supports all MOF pragmas, and specifically the include pragma. If a CIM class or CIM qualifier type to be added already exists in the target namespace with the same name (comparing case insensitively), this method raises :exc:`~pywbem.CIMError`. If a CIM instance to be added already exists in the target namespace with the same keybinding values, this method raises :exc:`~pywbem.CIMError`. In all cases where this method raises an exception, the mock repository remains unchanged. Parameters: mof_str (:term:`string`):
 A string with the MOF definitions to be compiled. namespace (:term:`string`):
 The name of the target CIM namespace in the mock repository. This namespace is also used for lookup of any existing or dependent CIM objects. If `None`, the default namespace of the connection is used. search_paths (:term:`py:iterable` of :term:`string`):
 An iterable of directory path names where MOF dependent files will be looked up. See the description of the `search_path` init parameter of the :class:`~pywbem.MOFCompiler` class for more information on MOF dependent files. verbose (:class:`py:bool`):
 Controls whether to issue more detailed compiler messages. Raises: IOError: MOF file not found. :exc:`~pywbem.MOFParseError`: Compile error in the MOF. :exc:`~pywbem.CIMError`: CIM_ERR_INVALID_NAMESPACE: Namespace does not exist. :exc:`~pywbem.CIMError`: Failure related to the CIM objects in the mock repository. """

        namespace = namespace or self.default_namespace

        # if not self._validate_namespace(namespace):  TODO
        #    self.add_namespace(namespace)
        self._validate_namespace(namespace)

        mofcomp = MOFCompiler(_MockMOFWBEMConnection(self),
                              search_paths=search_paths,
                              verbose=verbose)

        mofcomp.compile_string(mof_str, namespace)