'Initializes C{self.filename}.
If a file with this name already exists, asks if it should be
overwritten. Terminates with exit status 1, if the user does
not accept.'

def __init__(self, filename):

    if os.path.isfile(filename):
        response = raw_input(('A    file    named    %s    exists.    Overwrite    it    (y/n)?    ' % filename))
        if (response.lower() != 'y'):
            print('Performance    test    cancelled.')
            sys.exit(1)
    self.filename = filename
