Introduction to error handling

Introduction to Functions in Python

Hugo Bowne-Anderson

Instructor

The float() function

Screen Shot 2016-08-09 at 9.38.27 AM-4885.png

Passing an incorrect argument

float(2)

2.0

float('2.3')

2.3

float('hello')

<hr />---------------------------------------------------------------
ValueError                       Traceback (most recent call last)
<ipython-input-3-d0ce8bccc8b2> in <module>()
<hr />-> 1 float('hi')
ValueError: could not convert string to float: 'hello'

Passing valid arguments

def sqrt(x):
    """Returns the square root of a number."""
    return x ** (0.5)
sqrt(4)

2.0

sqrt(10)

3.1622776601683795

Passing invalid arguments

sqrt('hello')

------------------------------------------------------------------
TypeError                        Traceback (most recent call last)
<ipython-input-4-cfb99c64761f> in <module>()
----> 1 sqrt('hello')
<ipython-input-1-939b1a60b413> in sqrt(x)
      1 def sqrt(x):
----> 2     return x**(0.5)
TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'float'

Errors and exceptions

Exceptions - caught during execution
Catch exceptions with try-except clause
- Runs the code following try
- If there’s an exception, run the code following except

Errors and exceptions

def sqrt(x):
    """Returns the square root of a number."""
    try:
        return x ** 0.5
    except:
        print('x must be an int or float')


sqrt(4)

2.0

sqrt(10.0)

3.1622776601683795

sqrt('hi')

x must be an int or float

Errors and exceptions

def sqrt(x):
    """Returns the square root of a number."""
    try:
        return x ** 0.5
    except TypeError:
        print('x must be an int or float')

Screen Shot 2016-08-09 at 10.04.32 AM-4904.png

Errors and exceptions

sqrt(-9)

(1.8369701987210297e-16+3j)

def sqrt(x):
    """Returns the square root of a number."""
    if x < 0:
        raise ValueError('x must be non-negative')
    try:
        return x ** 0.5
    except TypeError:
        print('x must be an int or float')

Errors and exceptions

sqrt(-2)

-----------------------------------------------------------------
ValueError                      Traceback (most recent call last)
<ipython-input-2-4cf32322fa95> in <module>()
----> 1 sqrt(-2)
<ipython-input-1-a7b8126942e3> in sqrt(x)
      1 def sqrt(x):
      2     if x < 0:
----> 3         raise ValueError('x must be non-negative')
      4     try:
      5         return x**(0.5)
ValueError: x must be non-negative

Let's practice!

Introduction to Functions in Python