python - Django: failed to overwrite handler404 -

part urls.py (for testing):

old_handler404 = handler404 def custom_page_not_found(request, *args, **kwargs):     django.http import httpresponsenotfound     if request.path.startswith('/myapp/api'):         try:             return httpresponsenotfound( json.dumps( {'info': 'page not found'} ),                     content_type='application/json')         except exception e:             print 'exception:', e      #return httpresponsenotfound('page not found', content_type='text/html; charset=utf-8')     try:         res = old_handler404( request, *args, **kwargs )     except exception e:         print 'exception:', e     return res   handler404 = custom_page_not_found 

trying overwrite existing 404handler, rest apis (urls starting /myapp/api), return 404 , error messages in json if urls not matched, remainings, return 404 , existing not found pages if url not matched.

for /myapp/api, works fine. remainings, returned 500 instead of expected 404. no exception information shown.

any comments welcomed. thanks

update

exception: 'str' object not callable

update

how following codes? side-effects? in fact, in django app myapp, there several sub-apps. sub-apps finished others, , api sub-app finished me. not change/touch others' logic , codes. how following codes? welcomes welcomed. thanks.

from django.views.defaults import page_not_found old_page_not_found  #old_handler404 = django.views.defaults.page_not_found def custom_page_not_found(request, *args, **kwargs):     django.http import httpresponsenotfound     if request.path.startswith('/myapp/api'):         try:             return httpresponsenotfound( json.dumps( {'info': 'page not found'} ),                     content_type='application/json')         except exception e:             print 'exception:', e      #return httpresponsenotfound('page not found', content_type='text/html; charset=utf-8')     try:         res = old_page_not_found( request, *args, **kwargs)     except exception e:         print 'exception:', e     return res