Print a single field name/value pair.

def PrintField(self, field, value):
    """Print a single field name/value pair."""
    out = self.out
    out.write(' ' * self.indent)
    if self.use_field_number:
      out.write(str(field.number))
    else:
      if field.is_extension:
        out.write('[')
        if (field.containing_type.GetOptions().message_set_wire_format and
            field.type == descriptor.FieldDescriptor.TYPE_MESSAGE and
            field.label == descriptor.FieldDescriptor.LABEL_OPTIONAL):
          out.write(field.message_type.full_name)
        else:
          out.write(field.full_name)
        out.write(']')
      elif field.type == descriptor.FieldDescriptor.TYPE_GROUP:
        # For groups, use the capitalized name.
        out.write(field.message_type.name)
      else:
        out.write(field.name)

    if field.cpp_type != descriptor.FieldDescriptor.CPPTYPE_MESSAGE:
      # The colon is optional in this case, but our cross-language golden files
      # don't include it.
      out.write(': ')

    self.PrintFieldValue(field, value)
    if self.as_one_line:
      out.write(' ')
    else:
      out.write('\n')