SConstruct template with an action that renders jinja2 templates using data from an yaml file, while providing a markdown filter

SConstruct

# SConstruct template with an action that renders jinja2 templates
# using data from an yaml file, while providing a markdown filter.

import yaml
import jinja2
import markdown

if False:
    Environment = None


def markdown2html_filter(md):
    html = markdown.markdown(md, output_format='html5')
    return html


def render(target, source, env):
    assert len(target) == 1
    data = {}
    jinjafiles = []
    for filename in [str(s) for s in source]:
        if filename.endswith('.yaml'):
            with open(filename) as fd:
                d = yaml.load(fd)
                data.update(d)
        elif filename.endswith('.j2'):
            jinjafiles.append(filename)
    assert len(jinjafiles) == 1
    env = jinja2.Environment(loader=jinja2.FileSystemLoader('.'))
    env.filters['markdown'] = markdown2html_filter
    template = env.get_template(jinjafiles[0])
    with open(str(target[0]), 'w') as fdout:
        template.stream(data).dump(fdout)