How to use the nexusformat.nexus.tree.NXlog function in nexusformat

scan.interpret()
            entry = NXentry()
            entry.title = str(scan)
            entry.date = utils.iso8601(scan.date)  
            entry.command = scan.scanCmd 
            entry.scan_number = NXfield(scan.scanNum)
            entry.comments = '\n'.join(scan.comments)
            entry.data = self.scan_NXdata(scan)            # store the scan data
            entry.positioners = self.metadata_NXlog(scan.positioner, 
                                                    'SPEC positioners (#P & #O lines)')
            if hasattr(scan, 'metadata') and len(scan.metadata) > 0:
                entry.metadata = self.metadata_NXlog(scan.metadata, 
                                                     'SPEC metadata (UNICAT-style #H & #V lines)')

            if len(scan.G) > 0:
                entry.G = NXlog()
                desc = "SPEC geometry arrays, meanings defined by SPEC diffractometer support"
                # e.g.: SPECD/four.mac
                # http://certif.com/spec_manual/fourc_4_9.html
                entry.G.attrs['description'] = desc
                for item, value in scan.G.items():
                    entry.G[item] = NXfield(list(map(float, value.split())))
            if scan.T != '':
                entry['counting_basis'] = NXfield('SPEC scan with constant counting time')
                entry['T'] = NXfield(float(scan.T))
                entry['T'].units = 'seconds'
                entry['T'].description = 'SPEC scan with constant counting time'
            elif scan.M != '':
                entry['counting_basis'] = NXfield('SPEC scan with constant monitor count')
                entry['M'] = NXfield(float(scan.M))
                entry['M'].units = 'counts'
                entry['M'].description = 'SPEC scan with constant monitor count'

def metadata_NXlog(self, spec_metadata, description):
        '''
        return the specific metadata in an NXlog object
        '''
        from spec2nexus import utils
        nxlog = NXlog()
        nxlog.attrs['description'] = description
        for subkey, value in spec_metadata.items():
            clean_name = utils.sanitize_name(nxlog, subkey)
            nxlog[clean_name] = NXfield(value)
            nxlog[clean_name].original_name = subkey
        return nxlog