04 Functional Programming in Python

Python workshop by Ebad ullah Qureshi
Instructor: Ebad ullah Qureshi
Email: ebadullah.qureshi@rutgers.edu
N2E Coding Club
Python Workshop
Functional
Programming

Time Conversion – Problem
2
Given a time in 12-hour AM/PM format, convert it to military (24-hour) time.
Note: Midnight is 12:00:00AM on a 12-hour clock, and 00:00:00 on a 24-hour clock. Noon is
12:00:00PM on a 12-hour clock, and 12:00:00 on a 24-hour clock.
Input Format
A single string containing a time in 12-hour clock format (i.e.: hh:mm:ssAM or hh:mm:ssPM),
where 01≤hh≤12 and 00≤mm,ss≤59.
Constraints
All input times are valid, example, 07:05:45PM.
Output Format
Convert and print the given time in -hour format, where 00≤hh≤23, example, 19:05:45.
Testing
Test your program for 07:05:45AM, 12:05:45AM, 07:05:45PM, and 12:05:45PM.

Python workshop by Ebad ullah Qureshi 3
Time Conversion – Starting out
# Getting input
time12 = input("Enter time in hh:mm:ssAM or hh:mm:ssPM “)
# time12 and time24 have common minutes and seconds [:mm:ss]
time24 = time12[2:8]
# str12 format: hh:mm:ssAM or hh:mm:ssPM
am_or_pm = time12[8]
# Slicing hours
hour = time12[0:2]

Time Conversion – Conditional Block
if am_or_pm == 'A':
# for str12 01:00AM to 11:59AM
if hour != '12':
time24 = hour + time24
# for str12 12:00AM to 12:59AM
else:
time24 = "00" + time24
else:
# for str12 01:00PM to 11:59PM
if hour != '12':
hr = int(hour) + 12
time24 = str(hr) + time24
# for str12 12:00PM to 12:59PM
else:

Time Conversion – Program Output
5
print('Time in 24-hour clock format:', time24)
› Enter time in hh:mm:ssAM or hh:mm:ssPM 07:05:45AM
› Time in 24-hour clock format: 07:05:45
› Enter time in hh:mm:ssAM or hh:mm:ssPM 07:05:45PM
› Enter time in hh:mm:ssAM or hh:mm:ssPM 12:05:45AM
› Enter time in hh:mm:ssAM or hh:mm:ssPM 12:05:45PM

Introducing Functions I
• In the previous problem, the program ran 4 times to test 4 inputs and it was dependent upon
the user’s valid input
• A time_conversion function would be very helpful here
• The user’s input can be validated separately from the function so that the function always
receives a valid input and the function can be reused as many times to test various inputs
• A function is a block of organized, reusable code that is used to perform a single, related action
• Functions provide better modularity for your application and a high degree of code reusing

Introducing Functions II
# Previous Examples of functions you’ve already seen
print('Hello world')
range(5, 17, 2)
len('python')
• The words in front of the parentheses are function names
• The values inside the parenthesis are function arguments

Defining and Calling a Function
8
# defining a function
def hello():
print('hello world')
# calling the function
hello()
› hello world

Arguments and Return Statement
9
def add(num1, num2): # num1 and num 2 are arguments
return num1 + num2 # result is returned
# Function Calling
total = add(7, 9)
print(total)
› 16
Function returning the sum of 2 numbers

Flexible Number of Arguments
10
def add_numbers(*args):
total = 0
for num in args:
total += num
return total
print(add_numbers(5, 6, 8, 4, 2))
print(add_numbers(234, 543))
print(add_numbers(34, 56, 78, 5, 5.67, 2.45, 5*4))
› 25
› 777
› 201.11999999999998
Function to return the sum of numbers passed as argument

More about arguments
11
def cool_function(a, b=4, c=10):
# b and c are default value arguments
print('a is', a, 'b is', b, 'c is', c)
cool_function(38, 49) # a&b are passed c takes its default value
cool_function(54, c=74) # c is keyword argument, b is default argument
cool_function(c=72, a=23)# a&c are keyword arguments, b is default argument
data = [45, 35, 67] # a = data[0], b = data[1], c = data[2]
cool_function(*data) # * unpacks the list and passes it to the function
› a is 38 b is 49 c is 10
› a is 54 b is 4 c is 74
› a is 23 b is 4 c is 72
› a is 45 b is 35 c is 67

Time Conversion – Function
def time_conversion(time12):
time24 = time12[2:8]
am_or_pm = time12[8]
hour = time12[0:2]
if am_or_pm == 'A':
if hour != '12':
else:
time24 = "00" + time24
else:
if hour != '12':
hr = int(hour) + 12
time24 = str(hr) + time24
else:
return time24

Time Conversion – Testing the Function
13
# calling the function
print(time_conversion('07:05:45AM'))
print(time_conversion('12:05:45AM'))
print(time_conversion('07:05:45PM'))
print(time_conversion('12:05:45PM'))
› 07:05:45
› 00:05:45
› 19:05:45
› 12:05:45

Python Modules
14
There are 3 main types of modules;
1. Those you write yourself
2. Those you install from external resources
3. Those that are preinstalled with Python
The last type is called the standard library and has many useful functions

Python Standard Library
15
• Python’s extensive standard library is one of its main strengths as a language
• Some useful modules are;
 string
 re
 datetime
 math
 random
 os
 socket
 email
 json
 sys
 and much more

Modules in Python Standard library
16
• Some of the Python Modules in the standard library are written in Python, and some are
written in C
• Most are available on all platforms, but some are windows or Unix specific
• Many third-party Python modules are stored on the Python Package Index (PyPI)
• Modules are installed using a program called pip
• To install, go to the command line (command prompt on windows) and enter
> pip install library_name
• An alternate way to install is through the Project Interpreter on Pycharm
• Some modules have prebuilt binaries that are normal executable files for Windows and let
you install them with a GUI in the same way you would install other programs.
• Use the modules in your program using the import keyword

Gift Card Winners – Problem
17
import random
# random.randint(a,b) generates a random number N such that a <= N <= b
print(random.randint(1, 10))
› 7
As a General manager, you are responsible to give away a Gift Card to a raffle winner among your
top 10 performers. Write a python script to generate a random number that would correspond to
the winner of this week’s prize.

Gift Card Winners – Alternate Solution
18
from random import randint
# randint(a,b) generates a random number N such that a <= N <= b
print(randint(1, 10))
› 4
• In the previous solution, the whole module was imported when we only required the randint()
function
• There is an alternate syntax for only importing functions that are required in the program

Average of 10 random numbers – Problem
19
from statistics import mean as avg
import random as r
numbers = []
for _ in range(10):
numbers.append(r.randint(1, 50))
print(numbers)
print(avg(numbers))
› [47, 26, 34, 3, 8, 4, 43, 34, 44, 11]
› 25.4
Generate a list of 10 random numbers between 1 and 50 inclusive and calculate its average.
Achieve this by importing the random module and the mean function in the statistics module.
Rename the random module r and the mean function avg

Lambdas
20
# function to convert temperature in Kelvin to temperatures in degree
celsius
def kelvin_to_celsius(temperature):
return temperature – 273
print(kelvin_to_celsius(298))
# lambda function
result = (lambda temperature: temperature - 273)(250)
print(result)
› 25
› -23
• Alternate way of creating functions – lambda syntax
• Functions created this way are known as anonymous and most commonly used when passing
a simple function to another function

map() and filter() function
21
• The built-in functions map and filter are very useful higher order functions that operate on list
(or other iterables
• The function map takes a function and an iterable as arguments, and returns a new iterable
with the function applied to each argument
• The function filter filters an iterable by removing items that don’t match a predicate (function
that returns a Boolean)

map() and filter() function
22
kelvin_temperatures = [298, 278, 305, 245, 0, 100, 300, 400]
# convert all the temperatures in the above list into celsius
celsius_temperatures = list(map(kelvin_to_celsius, kelvin_temperatures))
print(celsius_temperatures)
# filtering out temperatures below freezing point
temp_below_zero = list(filter(lambda x: x < 0, celsius_temperatures))
print(temp_below_zero)
› [25, 5, 32, -28, -273, -173, 27, 127]
› [-28, -273, -173]

Instructor: Ebad ullah Qureshi
Email: ebadullah.qureshi@rutgers.edu
N2E Coding Club
Python Workshop
Thank You!
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04 Functional Programming in Python

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