Section 10: Debugging, Raising Exceptions, and Doctest

Question 1

What are the steps for a Doctest?

Answer 1

Steps:

1. import doctest in program
2. Call doctest.testmod()

If fails ⇒ show what the expected result should be

Ex:

```python
def add(x, y):
‘’’ (num, num) -> num Returns the sum of x and y
sum of x and y
»> add(2,2)
4
»> add(-2, 3)
1
»> add(1.2, 3.5)
4.7
‘’’

summation = x*y
return summation 

import doctest
doctest.testmod()
~~~

Question 2

What does doctest.testmod() do?What does

Answer 2

What does doctest.testmod() do?

• Executes each line in docstring that begins with ‘>>>’
• Compare the results obtains with predicted valueIf they do not mach: print that test has failed and whyIf match: nothing is displayed

Question 3

Define

Software bug:

Answer 3

<aside>
💡 Software bug: error or fault in program thatproduces incorrest or unexpected results

</aside>

• Debugging refers to the process of removing bugs or errors from a program

Question 4

Types of Errors:

Answer 4

1. Stylistic Errors:Functionality of your code is not affected.
   Hard to read
2. Syntax Errors:Problems with syntax
3. Runtime Errors:Problems with code is executed (if there were no syntax errors)
4. Logical Errors:No syntax or runtime errors, but not the required result

Question 5

What happens once an exception is raised?

Answer 5

When exception is raised: Python prints traceback which contains lots useful info used to debug programs

Question 6

What are Logical Errors?

Answer 6

• Refers to mistakes in the logic of the code → unexpected output
• Cannot automatically warm us
• Solve: break program down into simpler components

Two Main ways of debugging:

1. The print statement (lazy man’s debugger)
2. The debugger
3. Rubber DuckingExplaining the problem to someone else might help find a solution

Question 7

Define

Exceptions:

Answer 7

• An exception is when an event which occurs during the execution of the program and disrupts the normal flow of the program’s instructions
• When asked to do something that does not make sense

IndexError, TypeError, ValueError

Question 8

Exceptions:

IndexError

Answer 8

```python
s = ‘Monday’
c = s[10]
~~~

Trying to access the character that does not exists

Question 9

Exception

TypeError

Answer 9

TypeError:

```python
s = ‘Monday’
for c in s:
if c > 0 …

~~~

Comparing a string to an integer

Question 10

Exceptions

ValueError

Answer 10

ValueError

```python
def is_prime(n)
if n <=1:
~~~

Primality is not defined for numbers smaller than 2

Question 11

How to raise an exception?

Answer 11

When want to communicate to a user that some error occurred during execution, decide deliberately stop execution of your code by raising exception

Generally:

```python
raise<some_exception>(message)
~~~</some_exception>

• message optional: highly recommended
• Type of exception: NameError, TypeError, ValueError, IndexError, ZeroDivisionError