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One of my friends who works on JAVA asked me how do I handle checked and unchecked exceptions in Python. I haven't heard these terms before, so I googled around to find out what is checked and unchecked exception. I didn't find anything related to this kind of exception in Python.

Do we have a concept of checked and unchecked exceptions in Python? If no, then by default all the exceptions are checked or unchecked?

Thank you in advance!

Prateek Gupta
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    Almost no one but Java has checked exceptions. – user2357112 Sep 04 '20 at 05:23
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    Python is not compiled, so checked exceptions don't make much sense. See https://stackoverflow.com/questions/1591319/python-how-can-i-know-which-exceptions-might-be-thrown-from-a-method-call – Selcuk Sep 04 '20 at 05:23

2 Answers2

8

Checked exceptions are not a thing in Python. But Python does have some similarities in the exception class hierarchy. Here is the Java structure:

source

In Java you have to declare in the method signature if the method will throw an Exception or any class that inherits from Exception, but not the RuntimeException. This rule is called checked exceptions.. it forces the user to consider them or the application will not compile.

In Python we still have a similar concept, but no enforcement. You may have heard before that it's bad style to do a bare except statement, and at the very least you should choose to catch Exception

try:
   foo()
except: # bad!
   bar()

try:
   foo()
except Exception: # somewhat better!
   bar()

This is because in Python Exception extends from BaseException and a bare except will catch everything. For example, you probably don't want to catch ctrl+c which raises a KeyboardInterrupt. If you do a bare except:, then KeyboardInterrupt will be caught, but if you do a except Exception: you will let this bubble up and stop the application. That is because KeyboardInterrupt extends BaseException and not Exception and therefore wont be caught!

flakes
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-1

Java have checked and unchecked exceptions because Java is a complied programming language, checked exception comes in compiling. In python, there is no such exception because Python is an interpreted language.

Jaspreet Kaur
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    This has nothing to do with the language being compiled or interpreted. Although Java checked exceptions are done during compile, that is not inherently why they exist, but rather an implementation detail. There are many compiled languages that have no concepts of exceptions at all. – flakes Sep 04 '20 at 05:52
  • I don't know why this was down-voted, given it's technically correct. That said, it's worth pointing out that with the introduction of [PEP484](https://www.python.org/dev/peps/pep-0484/), Python does have type checking that can be done pre-runtime (it's usually executed as part of unit tests), where they could have done checked exception. That said, PEP484 does not cover checked exceptions. – Jack Leow Jan 28 '22 at 12:59