Learning Python: Functions

What is a Function

A function takes a set of inputs and produces an output. Eg:

>>>type(32)
<class 'init'>

Here type is a function that takes 32 as an input and produces its class.

Some Built-in functions

• max : gives the “largest character” in the string

  >>>max('Hello world')
  'w'
  

• min : gives the “smallest character” in the string

  >>>min('Hello world')
  ' '
  

• len : gives the number of characters in the string

  >>>len('Hello world')
  11
  

• Type conversion functions

  • int : takes any value and converts it to an integer, if it can, or complains otherwise

    >>>int('32')
    32
    >>>int('Hello')
    ValueError: invalid literal for int() with base 10: 'Hello'
    >>>int(3.99999)
    3
    >>> int(-2.3)
    -2
    

  • float : takes integers and strings, and converts them to floating-point numbers

    >>> float(32)
    32.0
    >>> float('3.14159')
    3.14159
    

  • str : converts its argument to a string

    >>> str(32)
    '32'
    >>> str(3.14159)
    '3.14159'
    

• Math Functions

  • Need to import it with the import math command.
  • log_10 : logarithm in base 10

    >>> ratio = signal_power / noise_power
    >>> decibels = 10 * math.log10(ratio)
    

  • pi

    >>> degrees = 45
    >>> radians = degrees / 360.0 * 2 * math.pi
    

  • sin

    >>> math.sin(radians)
    0.7071067811865476
    

  • sqrt

    >>> math.sqrt(2) / 2.0
    0.7071067811865476
    

• Random numbers

  • The random module provides functions that generate pseudorandom numbers

    import random
    
    for i in range(10):
      x = random.random()
      print(x)
    

    

  • randint : takes two inputs and produces a random integer in the range

    >>> random.randint(5,10)
    7
    >>> random.randint(5,10)
    10
    

  • choice : chooses an element from a sequence at random

    >>> t = [1, 2, 3]
    >>> random.choice(t)
    2
    >>> random.choice(t)
    3
    

Defining functions

The defining feature of programming languages is their ability to have user defined functions.

In python we define functions in the following way:

To call the above function you just type

>>> print_lyrics()
I'm a lumberjack, and I'm okay.
I sleep all night and I work all day.

If you have defined a function A already in your code, you can use it inside a function B as long as function B comes after function A in the flow of execution.

To return a result from a function, we use the return statement in our function

def addtwo(a, b):
    added = a + b
    return added

x = addtwo(3, 5)
print(x)

# Code: http://www.py4e.com/code3/addtwo.py

void function: A function that does not return a value.

>>> print(print_lyrics())
None
>>> print(type(None))
<class 'NoneType'>

Why functions

• name a group of statements; program easier to read, understand, and debug
• eliminates repetitive code; changes in one place
• debug the parts one at a time and then assemble them into a working whole
• well-designed functions are useful for many programs; write and debug once; reuse it

Exercise

Solutions

Exercise 4

inpHours = input('Enter Hours: ')

try:
    hour = float(inpHours)
except:
    print('Error, please enter numeric input')
    exit(0)

inpRate = input('Enter Rate: ')

try:
    rate = float(inpRate)
except:
    print('Error, please enter numeric input')
    exit(0)

def computepay(h, r):
    if h <= 40 :
        pay = r * h
    else:
        pay = (r * 40) + (1.5*r*(h-40))
    print('Pay:', pay)

computepay(hour, rate)

Exercise 5

inp = input('Enter score: ' )
try:
    s = float(inp)
except :
    print('Bad Score')
    quit()

def computegrade(score):
    if score > 1:
        return 'Bad score'
    elif score >= 0.9:
        return 'A'
    elif score >= 0.8:
        return 'B'
    elif score >= 0.7:
        return 'C'
    elif score >= 0.6:
        return 'D'
    elif score >= 0:
        return 'F'
    else:
        return 'Bad score'

grade = computegrade(s)

print(grade)