python - Changing the default ValueError of file.index -

i using file.index search string in file.

def ifstringexistsinfile(self,path,linetextcheck):     file = open(path).read()     if file.index(linetextcheck):         print (linetextcheck + " found in: " + path)     else:         raise valueerror (linetextcheck + " not found in: " + path) 

my issue if not find string, automatically raises default valueerror , not go "else" code contains custom valueerror:

valueerror: substring not found 

is there way change default valueerror?

currently, way came wrap sentence "try except", so:

def ifstringexistsinfile(self,path,linetextcheck):     file = open(path).read()     try:         if file.index(linetextcheck):             print (linetextcheck + " found in: " + path)     except:             raise valueerror(linetextcheck + " not found in: " + path) 

any better way appreciated. thank in advance!

any better way appreciated

you solved how should solved.

note can create own exception creating class inherits baseexception, needed.