This is an example of how Python's features get misused in ways that hint at symbolic programming in Lisp.

python_vs_lisp

# In Python it is common (though probably inadvisable) to
# use Exceptions for flow control in situations that are
# really not that exceptional. The Exception classes
# function as symbols for what is essentially symbolic
# programming using the exception handling machinery
# for the actual flow control.

class ValidationError(Exception):
    pass

class RouteNotFound(Exception):
    pass

def handler(request):
    try:
        validate_request(request)
    except ValidationError:
        handle_validation_error(request)
    except RouteNotFound:
        handle_route_not_found(request)

;; in Common Lisp or similar you could do something like this
;; where the validate-request function just returns a symbol
;; instead of raising an exception, and normal case matching
;; on the symbol for flow control.

(defun handler (request)
  (let ((result (validate-request request)))
    (case request
      (validation-error (handle-validation-error request))
      (route-not-found (handle-route-not-found request)))))