code: def sub_template(template,template_tag,substitution):
      '''make a substitution for a template_tag in a template
      '''
      template = template.replace(template_tag,substitution)
      return templatf sub_template(template,template_tag,substitution):
      '''make a substitution for a template_tag in a template
      '''
      template = template.replace(template_tag,substitution)
      return template
docs: make a substitution for a template_tag in a template