Exception
Handle Exception
try:
	clause
except ExceptI, errorInfo:
	if ExceptI is raised, execute this block
except ExceptII, errorInfo:
	if ExceptII is raised, execute this block
else:
	if no exception, execute this block
finally:
	this would always be executed
Raise Exception
raise Exception(errorInfo)
Python Exception Hierarchy
Raise and Handle
#!/usr/bin/python

def div(a, b):
    if b == 0:
        raise ZeroDivisionError("Denominator is zero ...");
    return a/b;

if __name__ == '__main__':
    try:
        div(1, 0);
    except Exception, err:
        print err.args, err;
assert
  • If the expression is false, Python raises an AssertionError exception
    • #!/usr/bin/python

def div(a, b):
    assert b != 0, 'AssertionError: Divided by zero ...';
    return a/b;

if __name__ == '__main__':
    try:
        div(1, 0);
    except Exception, err:
        print err.args, err;
  • python -O Exception.py, turn off assertion
    • # Exception.py
#!/usr/bin/python

def getString():
    return "Hello World!"

if __name__ == '__main__':
    s = getString();
    assert s == "Hello", "string is not correct ..."
    print s # Hello World!
    Traceback
    #!/usr/bin/python

import traceback

if __name__ == '__main__':
    try:
        div(1, 0);
    except Exception, err:
        print err.args, err;
        traceback.print_exc();
    User-Defined Exceptions
    #!/usr/bin/python

class definedExcept(Exception):
    def __int__(self, arg):
        self.args = arg;

def div(a, b):
    if b == 0:
        raise definedExcept("Defined Exception ...");
    return a/b;

if __name__ == '__main__':
    try:
        div(1, 0);
    except Exception, err:
        print err.args, err;
    Reference