old_contents: #!/usr/bin/env python3
  """Provide the standard Python string.Template engine."""
  
  from __future__ import print_function
  
  
  from string import Template
  
  from . import Engine
  
  
  class StringTemplate(Engine):
  
      """String.Template engine."""
  
      handle = 'string.Template'
  
      def __init__(self, template, **kwargs):
          """Initialize string.Template."""
          super(StringTemplate, self).__init__(**kwargs)
  
          self.template = Template(template)
  
      def apply(self, mapping):
          """Apply a mapping of name-value-pairs to a template."""
          return self.template.substitute(mapping)
  
new_contents: #!/usr/bin/env python3
  """Provide the standard Python string.Template engine."""
  
  from __future__ import print_function
  
  
  from string import Template
  
  from . import Engine
  
  
  class StringTemplate(Engine):
  
      """String.Template engine."""
  
      handle = 'string.Template'
  
      def __init__(self, template, tolerant=False, **kwargs):
          """Initialize string.Template."""
          super(StringTemplate, self).__init__(**kwargs)
  
          self.template = Template(template)
          self.tolerant = tolerant
  
      def apply(self, mapping):
          """Apply a mapping of name-value-pairs to a template."""
          if self.tolerant:
              return self.template.safe_substitute(mapping)
  
          return self.template.substitute(mapping)
  
subject: Implement tolerant handling in string.Template engine.