Question

I tried to define my own exception class in python 2.7, deriving from BaseException.

class NestedCommentException(BaseException):
    """
    Exception for nested comments
    """
    def __init__(self, file_path, list_lines):
        self.file_path = file_path
        self.list_lines = list_lines

    def __repr__(self):
        return self.__str__()

    def __str__(self):
        return 'File {0} contains nested comments at lines {1}'.format(self.file_path, ', '.join(self.list_lines))

But when throwing it, it cannot be printed: raise NestedCommentException(file_path, list_lines) triggers

Traceback (most recent call last):
  File "D:\DATA\FP12210\My Documents\Outils\SVN\05_impl\2_tools\svn_tag_setup.py", line 85, in <module>
    tag_checks()
  File "D:\DATA\FP12210\My Documents\Outils\SVN\05_impl\2_tools\svn_tag_setup.py", line 66, in tag_checks
    check_nested_comments(ddl_path)
  File "D:\DATA\FP12210\My Documents\Outils\SVN\05_impl\2_tools\svn_tag_setup.py", line 54, in check_nested_comments
    raise NestedCommentException(file_path, list_lines)
NestedCommentException: <unprintable NestedCommentException object>

Can you please explain why this happens, even if I defined __str__ and __repr__ methods ?

Answer 1

My guess is that you have unicode in file_path or list_lines variables dues to which it is not being printed on a console without unicode capabilities.

or any other exception in __str__ can cause such strange behavior, best way is to catch exception and see whats is happening, use debugger too

def __str__(self):
    try:
        s =  'File {0} contains nested comments at lines {1}'.format(self.file_path, ', '.join(self.list_lines))
    except Exception,e:
        print "-----",type(e),e
    return s