Unremovable assert

constraint.py

# Assertions can be removed by command flags,
# this can not

class ConstraintError(AssertionError):
    """"""


def constraint(condition, message=''):
    """
    Usage::
    
        def foo(var):
            constraint(isinstance(var, str), 'var must be a str')
            
            #... more code
    
    """
    if not condition:
        raise ConstraintError(message)