Exceptions

ImportError: an import fails;
IndexError: a list is indexed with an out-of-range number;
NameError: an unknown variable is used;
SyntaxError: the code can't be parsed properly;
TypeError: a function is called on a value of an inappropriate type;
ValueError: a function is called on a value of the correct type, but with an inappropriate value.

Exception Handling

To handle exceptions, and to call code when an exception occurs, you can use a try/except statement. Multiple exceptions can also be put into a single except block using parentheses, to have the except block handle all of them. An except statement without any exception specified will catch all errors.

Finally

To ensure some code runs no matter what errors occur, you can use a finally statement. The finally statement is placed at the bottom of a try/except statement.

try:
  a=0
  b=1
  print(a/b)
  #print(b/a)
  print(a+"a")
except ZeroDivisionError:
  print ("Error!")
except (ValueError,TypeError):
  print ("Error 2!")
except:
  print(f'Unknown error: {sys.exc_info()}')
else:
  print('No errors')
finally:
  print("Bye bye")

0.0
Error 2!
Bye bye

Raising Exceptions

Use raise statement Exceptions can be raised with arguments that give detail about them.

print(1)
raise ValueError
print(2)

1
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-75-990863ff3a0f> in <module>()
      1 print(1)
----> 2 raise ValueError
      3 print(2)

ValueError:

try:
  name = "123"
  raise NameError("Invalid Name!")
except NameError as e:
  print(f'Name error: {e}')
print (2)

Name error: Invalid Name!
2