nCoda Lychee Docs

Source code for lychee.converters.outbound.mei

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# Program Name:           Lychee
# Program Description:    MEI document manager for formalized document control
# Filename:               lychee/converters/
# Purpose:                Converts a Lychee-MEI document to a more conventional MEI document.
# Copyright (C) 2016, 2017, 2018 Christopher Antila
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License along
# with this program.  If not, see <>.
Convert a Lychee-MEI document to a standard MEI document.

.. danger:: This module is not fully implemented yet.

.. warning::
    This module is intended for internal *Lychee* use only, so the API may change without notice.
    If you wish to use this module outside *Lychee*, please contact us to discuss the best way.

.. tip::
    We recommend that you use the converters indirectly.
    Refer to :ref:`how-to-use-converters` for more information.

.. note:: This is an outbound converter that does not emit signals directly. Refer to the
    :mod:`lychee.signals.outbound` module for more information.

from fractions import Fraction

from lxml import etree

from lychee import exceptions
from lychee.namespaces import mei, xml

_ERR_INPUT_NOT_SECTION = 'LMEI-to-MEI did not receive a <section>'


[docs]def convert(document, **kwargs): ''' Convert a Lychee-MEI document into an MEI document. :param document: The Lychee-MEI document. :type document: :class:`xml.etree.ElementTree.Element` or :class:`xml.etree.ElementTree.ElementTree` :returns: The corresponding MEI document. :rtype: :class:`xml.etree.ElementTree.Element` or :class:`xml.etree.ElementTree.ElementTree` :raises: :exc:`lychee.exceptions.OutboundConversionError` when there is a forseeable error. ''' if isinstance(document, etree._Element) and mei.SECTION == document.tag: return convert_raw(document) else: raise exceptions.OutboundConversionError(_ERR_INPUT_NOT_SECTION)
[docs]def convert_raw(document): ''' Convert a Lychee-MEI document into an MEI document without verifying that it is an MEI section. ''' if len(document) > 0: document = create_measures(document) rewrite_beam_spans(document) return wrap_section_element(document)
[docs]def wrap_section_element(section): ''' Wrap a <section> element in <score>, <mdiv>, <body>, <music>, and <mei> so that it can stand as an independent document. :param section: The <section> eleemnt to wrap. :type section: :class:`xml.etree.ElementTree.Element` :returns: The corresponding <mei> element. :rtype: :class:`xml.etree.ElementTree.Element` ''' score = etree.Element(mei.SCORE) score.append(section) mdiv = etree.Element(mei.MDIV) mdiv.append(score) body = etree.Element(mei.BODY) body.append(mdiv) music = etree.Element(mei.MUSIC) music.append(body) post = etree.Element(mei.MEI) post.append(music) return post
[docs]def create_measures(lmei_section): ''' Convert a Lychee-MEI <section> without <measure> elements into an MEI section by adding <measure> elements at the expected place in the standard MEI hierarchy. :param lmei_section: The <section> to convert. :type lmei_section: :class:`xml.etree.ElementTree.Element` :returns: A converted <section>. :rtype: :class:`xml.etree.ElementTree.Element` .. note:: During conversion, the LMEI <section> is not modified. **Known Limitations** - Does not process tuplets. - Uses one meter signature for all staves. - Uses one meter signature for the whole <section> (cannot change). - Assumes 4/4 meter unless indicated otherwise with @meter.count and @meter.unit on the *first* <staffDef>. ''' # 0.) The poor man's deep copy. # This allows us to reuse LMEI elements in the MEI output, rather than deep copying later. l_section = etree.fromstring(etree.tostring(lmei_section)) # 1.) Assume or find a time signature. # Limitation: one time signature for all <staff>. # Limitation: one time signature for the whole <section>. # Limitation: metre must be indicated with @meter.count and @meter.unit on <staffDef>. first_staff_def = l_section.find('.//{tag}'.format(tag=mei.STAFF_DEF)) meter_count = float(first_staff_def.get('meter.count', 4)) meter_unit = float(first_staff_def.get('meter.unit', 4)) # NB: the "meter count factor" is the beat count we actually need in every measure meter_count_factor = meter_count / meter_unit # 1.a.) Make sure all the first <staffDef> knows the metre (in case we assumed it). first_staff_def.set('meter.count', str(int(meter_count))) first_staff_def.set('meter.unit', str(int(meter_unit))) # 2.) Set up the <section> and copy the <scoreDef> from LMEI to MEI. m_section = etree.Element(mei.SECTION) m_section.append(l_section.find(mei.SCORE_DEF)) # 3.) For each LMEI <staff> m_measures = {} # NB: in this dict, keys are measure number as int meas_nums = {} # NB: in this dict, keys are staff[@n] and values are the measure number most # recently processed for that <staff> for l_staff in l_section.iterfind(mei.STAFF): # in case we already had a <staff> with this @n, measure numbers don't start at 1 previous_measures = meas_nums.get(l_staff.get('n'), 0) highest_meas_num_in_this_staff = previous_measures # 4.) For each LMEI <layer> for l_layer in l_staff.iterfind(mei.LAYER): # 5.) Find enough stuff for an MEI <measure> and stick it in. # Limitation: does not handle tuplets. meas_num = previous_measures + 1 beat_count = 0.0 # We can't use beat_count to tell us when we're at the start of a <measure> (and should # therefore make new <measure> and <layer> elements) because there may be elements # without duration at the start of a <measure>. things_in_this_measure = 0 # Hold information about tuplets. # Keys are @xml:id of affected chord/note/rest/spacer (without leading #). # Value is a list of tuplet ratios as Fraction instances. When you multiply the @dur # of a note in a tuplet by these Fraction instances, you get the note's "beat count." # To save memory, remove values from the dictionary once the note is converted. tuplets = {} for l_elem in l_layer.iterfind('*'): if things_in_this_measure == 0: # create a new measure, or find it from a previous <staff> if meas_num in m_measures: m_meas = m_measures[meas_num] else: m_meas = etree.SubElement(m_section, mei.MEASURE, n=str(meas_num)) m_measures[meas_num] = m_meas # try to find this <staff> from a previous <layer> m_staff = m_meas.find('{tag}[@n="{n}"]'.format(tag=mei.STAFF, n=l_staff.get('n'))) if m_staff is None: m_staff = etree.SubElement(m_meas, mei.STAFF, n=l_staff.get('n')) m_layer = etree.SubElement(m_staff, mei.LAYER, n=l_layer.get('n')) # count the duration of this element (if relevant) if l_elem.tag not in _DURATION_HAVING_ELEMENTS: pass elif (beat_count == 0.0 and l_elem.get('dur') == '1' and l_elem.get(xml.ID) not in tuplets): # whole note as first thing in measure will always take the whole measure beat_count = meter_count_factor else: # It's "scaled" according to the meter-count factor. # Use float() so the division works properly. scaled_dur = 1.0 / float(l_elem.get('dur')) if l_elem.get('dots'): last_value_added = scaled_dur for _ in range(int(l_elem.get('dots'))): last_value_added /= 2.0 scaled_dur += last_value_added if l_elem.get(xml.ID) in tuplets: for each_tuplet in tuplets[l_elem.get(xml.ID)]: scaled_dur = scaled_dur * each_tuplet del tuplets[l_elem.get(xml.ID)] beat_count += scaled_dur # set up a <tupletSpan> if l_elem.tag == mei.TUPLET_SPAN: plist = l_elem.get('plist', '') plist = plist.replace('#', '') if plist != '': plist = plist.split(' ') tuplet_ratio = Fraction( int(l_elem.get('numbase', 0)), int(l_elem.get('num', 0)) ) for each_xmlid in plist: if each_xmlid in tuplets: tuplets[each_xmlid].append(tuplet_ratio) else: tuplets[each_xmlid] = [tuplet_ratio] m_layer.append(l_elem) things_in_this_measure += 1 if beat_count >= meter_count_factor: highest_meas_num_in_this_staff = max(highest_meas_num_in_this_staff, meas_num) beat_count = 0.0 meas_num += 1 things_in_this_measure = 0 # update "meas_nums" for next time we hit a <staff> with this @n meas_nums[l_staff.get('n')] = highest_meas_num_in_this_staff return m_section
[docs]def rewrite_beam_spans(m_section): ''' Modify the given section to replace <beamSpan> with <beam>, because Verovio doesn't support <beamSpan>. The element passed in does not actually need to be a section. It can be any parent of the elements we're interested in. ''' xml_ids = {} for el in m_section.iterfind('.//*'): if el.get(xml.ID): xml_ids[el.get(xml.ID)] = el for m_beamspan in m_section.iterfind('.//' + mei.BEAM_SPAN): beamspan_parent = m_beamspan.getparent() beamspan_parent.remove(m_beamspan) plist = m_beamspan.get('plist') nodes = [xml_ids[x[1:]] for x in plist.split()] parent = nodes[0].getparent() insertion_index = parent.index(nodes[0]) beam = etree.Element(mei.BEAM) for node in nodes: parent.remove(node) beam.append(node) parent.insert(insertion_index, beam) return m_section