• Practice building functions that use iteration and controlling their return values
• Practice manipulating lists (adding elements, removing elements, etc.)

• Interpreter: a program that executes other programs. Python programs require the Python interpreter to be installed on your computer so that they can be run.
• Python Shell: an interactive interpreter that can be accessed from the command line.
• Data Type: a specific kind of data. The Python interpreter uses these types to determine which actions can be performed on different data items.
• Exception: a type of error that can be predicted and handled without causing a program to crash.
• Code Block: a collection of code that is interpreted together. Python groups code blocks by indentation level.
• Function: a named code block that performs a sequence of actions when it is called.
• Scope: the area in your program where a specific variable can be called.

To get started, run pipenv install to create your virtual environment and pipenv shell to enter the virtual environment. Then run pytest -x to run your tests. Use these instructions and pytest's error messages to complete your work in the lib/ folder.

The local deli is putting in a new computerized queue to keep track of their customers and improve productivity. At the beginning of the day, the deli is empty so the queue should be represented by an empty list:

katz_deli = []

Write all of your code in lib/deli_counter.py

Build the line() function that shows everyone their current place in the line. If there is nobody in line, it should say "The line is currently empty.".

Build a function that a new customer will use when entering the deli. The take_a_number() function should accept two arguments, the list for the current line of people (katz_deli), and a string containing the name of the person joining the end of the line. The function should call out (i.e., print) the person's name along with their position in line.

Top-Tip: Remember that people like to count from 1, not from 0 like computers.

Build the now_serving() function which should call out (print) the next person in line and then remove them from the front. If there is nobody in line, it should call out (print) that "There is nobody waiting to be served!".

Example usage:

katz_deli = []

take_a_number(katz_deli, "Ada") #=> Welcome, Ada. You are number 1 in line.
take_a_number(katz_deli, "Grace") #=> Welcome, Grace. You are number 2 in line.
take_a_number(katz_deli, "Kent") #=> Welcome, Kent. You are number 3 in line.

line(katz_deli) #=> "The line is currently: 1. Ada 2. Grace 3. Kent"

now_serving(katz_deli) #=> "Currently serving Ada."

line(katz_deli) #=> "The line is currently: 1. Grace 2. Kent"

take_a_number(katz_deli, "Matz") #=> Welcome, Matz. You are number 3 in line.

line(katz_deli) #=> "The line is currently: 1. Grace 2. Kent 3. Matz"

now_serving(katz_deli) #=> "Currently serving Grace."

line(katz_deli) #=> "The line is currently: 1. Kent 2. Matz"

Hint: Review how to add and remove list elements as well as how to iterate with index numbers.

• W3Schools: Add List Items
• W3Schools: Remove a List Item
• How to Iterate a Python List With Index