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Exceptions

Understanding Python Exception

Python built-in exceptions

def simple_div(x,y):
    z = x / y
    return z

simple_div(2,2)

1
1.0

simple_div(0,2)

1
0.0

simple_div(2,0)

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---------------------------------------------------------------------------

ZeroDivisionError                         Traceback (most recent call last)

<ipython-input-3-95e9e8e0b13c> in <module>
----> 1 simple_div(2,0)


<ipython-input-1-69d8d8976ddb> in simple_div(x, y)
      1 def simple_div(x,y):
----> 2     z = x / y
      3     return z
      4 
      5 simple_div(2,2)


ZeroDivisionError: division by zero

0 is divisible by any number, but returns 0.
But a number cannot be divided by nothing (0).

This is an exception, a python exception, called in this case ZeroDivisionError.

simple_div(2,'a')

…is an exception called TypeError.

simple_div(2,a)

…is a NameError.

Catching Exceptions

Let’s catch exception ZeroDivisionError.

def simple_div_2(x,y):
    try:
        z = x / y
        return z
    except ZeroDivisionError:
        print("Divided by 0!")

simple_div_2(2,0)

1
Divided by 0!

try:
    print(simple_div_2(2,0))
except ZeroDivisionError:
    print("Divided by 0!")

1
2
Divided by 0!
None

Let’s catch exception TypeError.

def simple_div_3(x,y):
    try:
        z = x / y
        return z
    except TypeError:
        z = -1
        return z

simple_div_3(2,'a')

1
-1

Let’s catch exception NameError.

try:
    print(simple_div(2,a))
except NameError:
    print(-2)

1
-2

Let’s put it all together!

def simple_div_5(x,y):
    try:
        z = x / y
        return z
    except ZeroDivisionError:
        return ("Divided by 0!")
    except TypeError:
        z = -1
        return z

try:
    print(simple_div_5(2,2))
except NameError:
    print(-2)

1
1.0

try:
    print(simple_div_5(0,2))
except NameError:
    print(-2)

1
0.0

try:
    print(simple_div_5(2,0))
except NameError:
    print(-2)

1
Divided by 0!

try:
    print(simple_div_5(2,'a'))
except NameError:
    print(-2)

1
-1

try:
    print(simple_div_5(2,a))
except NameError:
    print(-2)

1
-2