python_training_and_exercise_on_Exceptions

python_training_and_exercise_on_Exceptions.md

Exceptions

Sharif Chowhdury

Software Engineer ( Circle FinTech Ltd. )

techsharif.com

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Errors

• Syntax errors
• Semantic errors
• Logical errors

Try Except

Basic

try:
	1 / 0
except ZeroDivisionError:
	print("You cannot divide by zero!")

Worse practice

try:
	1 / 0
except:
	print("You cannot divide by zero!")

Exception Hierarchy ( Example )

• BaseException
  • Exception
    • ArithmeticError
      • FloatingPointError
      • OverflowError
      • ZeroDivisionError
    • AssertionError

try:
	1 / 0
except ArithmeticError:
	print("You cannot divide by zero!")

Handling Multiple Exceptions raise

a = 5
b = 6


def divide_test(a,b):
	try:
		print(a / b)
	except TypeError:
		print("Please provide numbers")
	except ZeroDivisionError:
		print("You cannot divide by zero!")


divide_test(4,5)
divide_test(4,0)
divide_test(4,"asdf")

assert

Temperature = -1
assert (Temperature >= 0),"Colder than absolute zero!"

Custom Exception Classes

class StudentNumberError(Exception):
	def __init__(self):
		Exception.__init__(self,"Number of students should be non negetive integer") 

class Batch:
	def __init__(self, students):
		if type(students) == int and students >= 0:
			self.students = students
		else:
			raise StudentNumberError

Test 01

obj = Batch(5)
print(obj.students)

Test 02

obj = Batch(-1)
print(obj.students)

Test 03

try:
	obj = Batch(-1)
	print(obj.students)
except StudentNumberError:
	print("an error occur")

finaly

• Execute at the end

my_dictionary = dict()
try:
	value = my_dictionary["d"]
except KeyError:
	print("A KeyError occurred!")
finally:
	print("The finally statement has executed!")

else

• The else will only run if there are no errors raised.

test 01

my_dictionary = {"a":1, "b":2, "c":3}
try:
	value = my_dictionary["a"]
except KeyError:
	print("A KeyError occurred!")
else:
	print("No error occurred!")

Test 02

my_dictionary = {"a":1, "b":2, "c":3}
try:
	value = my_dictionary["d"]
except KeyError:
	print("A KeyError occurred!")
else:
	print("No error occurred!")