Generate a QGIS map PDF using python

pdf_generator.py

# coding=utf-8

# A simple demonstration of to generate a PDF using a QGIS project
# and a QGIS layout template.
#
# This code is public domain, use if for any purpose you see fit.
# Tim Sutton 2015

import sys
from qgis.core import (
    QgsProject, QgsComposition, QgsApplication, QgsProviderRegistry)
from qgis.gui import QgsMapCanvas, QgsLayerTreeMapCanvasBridge
from PyQt4.QtCore import QFileInfo
from PyQt4.QtXml import QDomDocument


gui_flag = True
app = QgsApplication(sys.argv, gui_flag)

# Make sure QGIS_PREFIX_PATH is set in your env if needed!
app.initQgis()

# Probably you want to tweak this
project_path = 'project.qgs'

# and this
template_path = 'template.qpt'

def make_pdf():
    canvas = QgsMapCanvas()
    # Load our project
    QgsProject.instance().read(QFileInfo(project_path))
    bridge = QgsLayerTreeMapCanvasBridge(
        QgsProject.instance().layerTreeRoot(), canvas)
    bridge.setCanvasLayers()

    template_file = file(template_path)
    template_content = template_file.read()
    template_file.close()
    document = QDomDocument()
    document.setContent(template_content)
    composition = QgsComposition(canvas.mapSettings())
    # You can use this to replace any string like this [key]
    # in the template with a new value. e.g. to replace
    # [date] pass a map like this {'date': '1 Jan 2012'}
    substitution_map = {
        'DATE_TIME_START': 'foo',
        'DATE_TIME_END': 'bar'}
    composition.loadFromTemplate(document, substitution_map)
    # You must set the id in the template
    map_item = composition.getComposerItemById('map')
    map_item.setMapCanvas(canvas)
    map_item.zoomToExtent(canvas.extent())
    # You must set the id in the template
    legend_item = composition.getComposerItemById('legend')
    legend_item.updateLegend()
    composition.refreshItems()
    composition.exportAsPDF('report.pdf')
    QgsProject.instance().clear()


make_pdf()

Is it possible to use a composer that is saved in the project file itself, rather than load it from a template?

Unfortunately, this does not seem to work on QGIS 2.8.3 anymore. The map canvas stays blank. Any Ideas on what API change may have caused this? Thanks!

I'm having the same blank map issue using QGIS 2.8.3. Maybe this is related--but a table item I have added is staying blank as well.

Blank map in Qgis 2.18.9 ... it seems that composition.getComposerItemById returns nothing. Any idea?

Would love to see an update/example of this for QGIS3.