How to use the moltemplate.ttree.PushLeftCommand function in moltemplate

which_stack=command.context_node)
                # Everything else must be saved for later.
                postprocessing_blocks = transform_blocks[1:]
            else:
                # If we already encountered a "movecm" "rotcm" or "scalecm"
                # then all of the command blocks must be handled during
                # postprocessing.
                postprocessing_blocks = transform_blocks

            for transform_block in postprocessing_blocks:
                assert(isinstance(block, basestring))
                if isinstance(command, PushRightCommand):
                    postprocessing_commands.append(PushRightCommand(transform_block,
                                                                    command.srcloc,
                                                                    command.context_node))
                elif isinstance(command, PushLeftCommand):
                    postprocessing_commands.append(PushLeftCommand(transform_block,
                                                                   command.srcloc,
                                                                   command.context_node))

        elif isinstance(command, WriteFileCommand):

            # --- Throw away lines containin references to deleted variables:---

            # First: To edit the content of a template,
            #        you need to make a deep local copy of it
            tmpl_list = []
            for entry in command.tmpl_list:
                if isinstance(entry, TextBlock):
                    tmpl_list.append(TextBlock(entry.text,
                                               entry.srcloc))  # , entry.srcloc_end))
                else:

# Everything else must be saved for later.
                postprocessing_blocks = transform_blocks[1:]
            else:
                # If we already encountered a "movecm" "rotcm" or "scalecm"
                # then all of the command blocks must be handled during
                # postprocessing.
                postprocessing_blocks = transform_blocks

            for transform_block in postprocessing_blocks:
                assert(isinstance(block, basestring))
                if isinstance(command, PushRightCommand):
                    postprocessing_commands.append(PushRightCommand(transform_block,
                                                                    command.srcloc,
                                                                    command.context_node))
                elif isinstance(command, PushLeftCommand):
                    postprocessing_commands.append(PushLeftCommand(transform_block,
                                                                   command.srcloc,
                                                                   command.context_node))


        elif isinstance(command, WriteFileCommand):

            # --- Throw away lines containin references to deleted variables:---

            # First: To edit the content of a template, 
            #        you need to make a deep local copy of it
            tmpl_list = []
            for entry in command.tmpl_list:
                if isinstance(entry, TextBlock):
                    tmpl_list.append(TextBlock(entry.text, 
                                               entry.srcloc)) #, entry.srcloc_end))
                else:

# Everything else must be saved for later.
                postprocessing_blocks = transform_blocks[1:]
            else:
                # If we already encountered a "movecm" "rotcm" or "scalecm"
                # then all of the command blocks must be handled during
                # postprocessing.
                postprocessing_blocks = transform_blocks

            for transform_block in postprocessing_blocks:
                assert(isinstance(block, basestring))
                if isinstance(command, PushRightCommand):
                    postprocessing_commands.append(PushRightCommand(transform_block,
                                                                    command.srcloc,
                                                                    command.context_node))
                elif isinstance(command, PushLeftCommand):
                    postprocessing_commands.append(PushLeftCommand(transform_block,
                                                                   command.srcloc,
                                                                   command.context_node))

        elif isinstance(command, WriteFileCommand):

            # --- Throw away lines containin references to deleted variables:---

            # First: To edit the content of a template,
            #        you need to make a deep local copy of it
            tmpl_list = []
            for entry in command.tmpl_list:
                if isinstance(entry, TextBlock):
                    tmpl_list.append(TextBlock(entry.text,
                                               entry.srcloc))  # , entry.srcloc_end))
                else:
                    tmpl_list.append(entry)

#break

                            raise InputError("Error: center-of-mass transformations are not yet implemented\n"
                                             "       Avoid using \""+transform+"()\" transformations.\n")

                transform_blocks.append(transform_block)

            if len(postprocessing_commands) == 0:
                # The first block (before movecm, rotcm, or scalecm)
                # can be executed now by modifying the matrix stack.
                if isinstance(command, PushRightCommand):
                    matrix_stack.PushCommandsRight(transform_blocks[0].strip('.'),
                                                   command.srcloc,
                                                   which_stack=command.context_node)
                elif isinstance(command, PushLeftCommand):
                    matrix_stack.PushCommandsLeft(transform_blocks[0].strip('.'),
                                                  command.srcloc,
                                                  which_stack=command.context_node)
                # Everything else must be saved for later.
                postprocessing_blocks = transform_blocks[1:]
            else:
                # If we already encountered a "movecm" "rotcm" or "scalecm"
                # then all of the command blocks must be handled during
                # postprocessing.
                postprocessing_blocks = transform_blocks

            for transform_block in postprocessing_blocks:
                assert(isinstance(block, basestring))
                if isinstance(command, PushRightCommand):
                    postprocessing_commands.append(PushRightCommand(transform_block,
                                                                    command.srcloc,

elif isinstance(command, ScopeEnd):
            if data_atoms in files_content:
                for ppcommand in postprocessing_commands:
                    if data_masses in files_content:
                        xcm = CalcCM(files_content[data_atoms],
                                     files_content[data_masses],
                                     settings)
                    else:
                        xcm = CalcCM(files_content[data_atoms])
                    if isinstance(ppcommand, PushRightCommand):
                        matrix_stack.PushCommandsRight(ppcommand.contents,
                                                       ppcommand.srcloc,
                                                       xcm,
                                                       which_stack=command.context_node)
                    elif isinstance(ppcommand, PushLeftCommand):
                        matrix_stack.PushCommandsLeft(ppcommand.contents,
                                                      ppcommand.srcloc,
                                                      xcm,
                                                      which_stack=command.context_node)
                    files_content[data_atoms] = \
                        TransformAtomText(files_content[data_atoms],
                                          matrix_stack.M, settings)
                    files_content[data_ellipsoids] = \
                        TransformEllipsoidText(files_content[data_ellipsoids],
                                               matrix_stack.M, settings)

                for ppcommand in postprocessing_commands:
                    matrix_stack.Pop(which_stack=command.context_node)
                    #(same as PopRight())

            if isinstance(command.node, InstanceObj):

for ppcommand in postprocessing_commands:
                    if 'Data Masses' in files_content:
                        pass
                        #xcm = CalcCM(files_content['Data Atoms'],
                        #             files_content['Data Masses'],
                        #             settings)
                    else:
                        pass
                        #xcm = CalcCM(files_content['Data Atoms'])

                    if isinstance(ppcommand, PushRightCommand):
                        matrix_stack.PushCommandsRight(ppcommand.contents,
                                                       ppcommand.srcloc,
                                                       xcm,
                                                       which_stack=command.context_node)
                    elif isinstance(ppcommand, PushLeftCommand):
                        matrix_stack.PushCommandsLeft(ppcommand.contents,
                                                      ppcommand.srcloc,
                                                      xcm,
                                                      which_stack=command.context_node)
                    files_content['Data Atoms'] = \
                        TransformAtomText(Files_content['Data Atoms'],
                                          matrix_stack.M)

                for ppcommand in postprocessing_commands:
                    matrix_stack.Pop(which_stack = command.context_node)
                    #(same as PopRight())

            if isinstance(command.node, InstanceObj):
                if ((command.node.children != None) and 
                    (len(command.node.children) > 0)):
                    matrix_stack.PopStack()