This week, we started with
something that we have never learnt before: Exception. Exceptions should be
class objects. The exceptions are defined in the module Exception; it is a built-in
class and I can always build new exception as subclasses of it and the python
will automatically know it will deal with exceptions. The following Exception
can only used as a superclass classes for other exceptions. A typical look of Exception
will be this:
class E1(Exception):
"""
An exception
class that is a subclass of Exception.
"""
pass
class E2 (E1):
"""
An exception
class that is a subclass of E1.
"""
pass
def exception_raise_function(x) -> None:
try:
if something:
raise E1
else:
raise E2('hey, I’m E2')
except E1:
# can
print/return/etc. things
except E2:
# can
print/return/etc. things
In class Exception, a try statement
with an except clause that mentions a
particular Exception subclass, that clause also handles any exception classes
derived from that class. A exception message that coded within the bracket in
the raise statement can also be printed when this exception is been raised. A
test class could be designed to test the exception code:
def test_exception_raise_function(f, x) -> None:
"""
f is the name of the exception function, x is the input of the functions.
"""
try:
if f(x)
is None:
except E1:
except E2:
The raise of a exception
can sometimes return something long and messy. Yet, by using designed testing function,
one can see whether the exception function was correctly coded by the things it
returned.
Python raises exception in
case of errors, and I can design codes to deal with these errors. I can use the
try statements and except statements to raise exceptions when an error is
produced. All exceptions are designed/subclassed from the
built-in superclass, Exception class. I am still a little bit
confuse about the differences of put try and except statements into different
orders or levels of indented if statements, yet I think I have already got some
grasp about exception; I just need a bit more practice
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