Session 2 - Data Structures: List & Tuples

Today we will work with data structures in python. You will by the end of these sessions be able to use Lists and Tuples, read and Write to Files and work with the for and while loop.

List and tuples are two of the build-in datastructures in python.

Learning goals

After this week you will be able to:

  • Work with lists, tuples

  • Loop over sequences with a for, foreach & while loops.

  • Sort sequences using the build in sorted function and use its key parameter to perform custom sorting.

  • Read from files and write to files using the build in “open” function.

Materials

Exercises

Ex 0.1: Slicing

Solution

By using the slicing syntax change the following collections.

After slicing:

1['Hello', 'World', 'Huston', 'we', 'are', 'here'] should become -> ['World', 'Huston', 'we', 'are']
2['Hello', 'World', 'Huston', 'we', 'are', 'here'] -> ['Hello', 'World']
3['Hello', 'World', 'Huston', 'we', 'are', 'here'] -> ['are', 'here']
4['Hello', 'World', 'Huston', 'we', 'are', 'here'] -> ['are']
5['Hello', 'World', 'Huston', 'we', 'are', 'here'] -> ['Hello', 'Huston', 'are']
6['Hello', 'World', 'Huston', 'we', 'are', 'here'] -> ['here', 'are', 'we', 'Huston', 'World', 'Hello']
7('Hello', 'World', 'Huston', 'we', 'are', 'here') should become -> ['World', 'Huston', 'we', 'are']
8'Hello World Huston we are here' -> 'World Huston we'

Figure out more on your own and practice this a lot!

Ex 1: Build-in functions on lists

Create a list like this: names = ['George', 'Bejamin', 'Thomas', 'John']
Look at this list of pythons build in functions.
Try all of these (on a list you create). e.g len(names)
Not all will work on lists, but try it out, read the documentation, and see what works.

Ex 1.1: Is it a tuple or a list?

Solution

The following data should be presented as either a list or a tuple, or as a combination of both.
Your job is to choose the right one.
Hint: A list is a collection of the same type of data, a tuple is a record (e.g. in a database a record is called a row)

  1. Claus, 51, male, clbo@kea.dk, 31011970-1313

  2. Bmw, Toyota, Hyundai, Skoda, Fiat, Volvo

  3. Claus, Henning, Torben, Carl, Tine

  4. ‘Hello’, ‘World’, ‘Huston’, ‘we’, ‘are’, ‘here’

  5. Rolling Stones, Goats Head Soup, 31 August 1973, 46:56

  6. 40.730610, -73.935242, New York City, NY, USA; 31.739847, 65.755920, Kandahar, Kandahar Province, Afghanistan;

Ex 2: Sort a Text

Solution

  1. Create a function that takes a string as a parameter and returns a list.

  2. The function should remove all vowels and sort the consonants in alphabetic order, and the return the result.

Ex 3: Sort a list

Solution

  1. Create a list of strings with names in it. (l = [‘Claus’, ‘Ib’, ‘Per’])

  2. Sort this list by using the sorted() build in function.

  3. Sort the list in reversed order.

  4. Sort the list on the lenght of the name.

  5. Sort the list based on the last letter in the name.

  6. Sort the list in a way that the names that has an ‘a’ in it should be sorted first (still alphabetically).

Ex 4: Text editor plugin simulation

Solution

s = 'This is just a sample text that could have been a million times longer.\n\nYours Johnny'

  1. Count the number of characters including blank spaces.

  2. Count the number of characters excluding blank spaces.

  3. Count the number of words.

Ex 4: Files

Solution

  1. Create a file and call it lyrics.txt (it does not need to have any content)

  2. Create a new file and call it songs.docx and in this file write 3 lines of text to it.

  3. open and read the content and write it to your terminal window. * you should use both the read(), readline(), and readlines() methods for this. (so 3 times the same output).

Ex 5: Sort a list of tuples

Solution

1. Based on this list of tuples: [(1,2),(2,2),(3,2),(2,1),(2,2),(1,5), (10,4), (10, 1), (3, 1)]

2. Sort the list so the result looks like this: [(2, 1), (3, 1), (10, 1), (1, 2), (2, 2), (2, 2), (3, 2), (10, 4), (1, 5)]

Note

This is first sorted by the last element in the tuple and then the first element in the tuple.
You should do this in 1 step, but it might help you to try it out in 2 steps first.

List & Tuples exercises

Solution

quizes