input: Write a python function to generate an HTML template using string.Template.
  assert generate_html('My Website', 'Hello World!', 'This is my website!') == '<html><body><title>My Website</title><h1>Hello World!</h1>This is my website!</body></html>'
  assert generate_html('Test Title', 'Test Heading', 'Test content.') == '<html><body><title>Test Title</title><h1>Test Heading</h1>Test content.</body></html>'
  assert generate_html('Another Title', 'Another Heading', 'Another content.') == '<html><body><title>Another Title</title><h1>Another Heading</h1>Another content.</body></html>'
output: def generate_html(title, heading, content):
      from string import Template
      template = Template('<html><body><title>$title</title><h1>$heading</h1>$content</body></html>')
      return template.substitute(title=title, heading=heading, content=content)