05-functions.md

Python 05

1. Functions
2. Exercises
3. Project: Baby names NY

Project: Baby names NY

functions

A function is a group of connected statements (code) that perform a specific task.

A function usually looks like this:

def function_name( input_variables ):
   something happens
   if something is True:
       then something else
   else:
       then stuff here
   maybe even another thing
   return output_variables

• Functions help break our code into smaller and modular parts.
• Functions make larger codes more organized and manageable
• A function does not necessarily return something
• When called, the content of the function is executed sequentially.

Let's write a function which tells us if today is Monday. We will use the datetime package (provided with python), open your python shell:

• date refers to a "class" from the datetime package, which contains a function, today(), that returns today's date. Try it:

>>> from datetime import date
>>> date.today()
datetime.date(2019, 1, 28)

• datetime also provides a function which finds the day of the week for a specific date (https://docs.python.org/3/library/datetime.html#datetime.date.weekday):

>>> from datetime import date
>>> today = date.today()
>>> isitmonday = today.weekday()
>>> isitmonday
>>> 0 #Because I executed this on a Monday 

Now that we're able to determine if today is a Monday or not, let's write our function:

• Our function will take the date as an input_variable
• It will return a certain message if it is Monday and a different one if it isn't

from datetime import date

def monday_check(specimen_date):
    if specimen_date.weekday() == 0:
        message = "Monday again ... Go away Monday!"
    else:
        message = "Today is not a Monday!"
    return message

Let's now call our function in our script (to execute a script python3 script.py):

#IMPORTS
from datetime import date

#FUNCTIONS
def monday_check(specimen_date):
    if specimen_date.weekday() == 0:
        message = "Monday again ... Go away Monday!"
    else:
        message = "Today is not a Monday!"
    return message

#SCRIPT
print("This program will tell you if it is already the worst day of the week.")
today = date.today()
print( monday_check(today) )

Try this code: https://github.com/pythonclubmtl/learning_python3 -> ex_mondaycheck.py

Exercises

Perfect numbers

In number theory, a perfect number is a positive integer that is equal to the sum of its proper positive divisors, that is, the sum of its positive divisors excluding the number itself. Equivalently, a perfect number is a number that is half the sum of all of its positive divisors (including itself). The first perfect number is 6, because 1, 2, and 3 are its proper positive divisors, and 1 + 2 + 3 = 6. Equivalently, the number 6 is equal to half the sum of all its positive divisors: ( 1 + 2 + 3 + 6 ) / 2 = 6.

• Your function should input a number (any integer number)
• Your function should return the boolean value False or True

Hint: message = False affects the boolean value False to message. Not "false", False. False is not a string, not an integer, it is a boolean.

More exercises

• Go through: https://www.practicepython.org/exercise/2014/01/29/01-character-input.html
• Then this one: https://www.practicepython.org/exercise/2014/02/05/02-odd-or-even.html
• Next: https://www.practicepython.org/exercise/2014/03/05/05-list-overlap.html

Project: Baby names NY

The dataset Popular_Baby_Names_NY.csv presents a list of the most popular baby names for the city of New York between 2011-2016. As you might notice after exploring the dataset, a count and rank are provided per baby name, per ethnicity, per year, per sex. You can easily find the most popular baby name for a certain year and a certain ethnicity, but determining the most popular baby name for the year 2012, regardless of the ethnicity or sex is quite complicated.

For this project, you will have 3 tasks:

1. Create a function (get_csv_data) that inputs a path (as a string) and returns the content of a CSV file as a list which itself contains each column as a list (without the header): [[column_1], [column_2], ... , [column_n]]
2. Write a script that provides (use your get_csv_data function in it):

• The most popular female name for each year
• The most popular hispanic name for males between 2011-2016
• The most popular female name for any ethnicity between 2012-2015

string.lower() # Converts given string into lowercase and returns it
max(list) # Returns maximum value from a list
set(list) # Returns a list without any duplicates

A detailed solution for the first task (without using functions though, you will have to take care of that) is provided here.

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>>> You should now move on to the next session. <<< Feel like you need to review a few things in the previous session ?