Intro to Python: Labs

Welcome to the Python lab! Work through this sheet in pairs, making sure that you understand each bit of code before you move on.

If you get something wrong, let us know! Other people may have done the same thing; maybe you can help them.

1: Basics

Try the following in the Python REPL. What do they do?

• print "hello"
• print 'hello'
• print hello

Let's do some maths!

• 4 + 5
• 8 * 3
• 4 / 3
• 4.0 / 3
• 3 + 5 * 9

Adding Strings?

• "abc" + "def"
• "hello" + " " + "world"
• "123" + "5"

Variables!

• first = "hello"
• second = "world"
• first + " " + second
• type(first)

User input?

• name = raw_input("What is your name?")
• type(name)
• age = int(raw_input("What is your age?"))
• type(age)

2: Functions

In a file called person.py:

• Write a function called get_age that asks the user for their age, and returns it as an int
• Write another function called get_name, which does the same but for the users age
• Call both these functions and tell the user what you know about them!

##3: Loops In a file called loops.py:

• Write the following code: i = 0 while(i < 10): i = i + 1 print i

1: Counting

In the file counting.py, write a function called count that returns the numbers from 1 to 5 in a list. Call your function from __main__() and print the results to make sure it's doing the right thing

Remember to write a docstring for your module!

2: More counting!

In the file counting_arrays.py, write another function called count that takes a numerical argument n and returns the numbers from 1 to n in a list. The list should include the n. Again, write code in __main()__ to test your new count.

3: Evens

In the file evens.py, write a function called evens that takes a list of numbers and returns the sum of all the even numbers.

4: Tuples

In the file tuples.py, write two functions:

• partition should take a number and return a 2-tuple, with the number on the left if it's even, and on the right if it's odd. The other slot should be filled with the constant None
• partition_list, which takes a list of numbers and returns a 2-tuple of lists. It should use your partition function to split the input list into the odd numbers and the even numbers.

Stretch

Well done if you've come so far. Below are some harder labs that will take more time. Everyone should hopefully get at least this far :)

Stretch: Complex numbers

Investigate the complex numeric type. In a file called mandelbrot.py, write a function called mandelbrot that takes a number n and prints out the Mandelbrot Set using ascii characters in an n x n matrix.

Stretch: tic-tac-toe

Write a tic-tac-toe game. Firstly, it should print out an empty grid, then wait for input. Players take turns entering coordinates in the form (x, y). The game adds a O or an X in the right square, then prints out the grid again.

Make good use of functions to split up your code. For example, you could write a function print_grid which takes the grid state as an argument and prints it to the console.

Stretch: Write a single-player game where the computer plays against you. Are you better at Python than you are at tic-tac-toe? :)

Testing

In the shell, in the labs directory, execute python tests.py. If you've followed all the instructions and done well in the labs, all the tests should pass. If you get test failures, the output will show you where you've gone wrong.

Testing is an important part of any software development process. "Testing" code using __main__() methods is brittle, because you need to execute them manually - meaning you might forget and check in buggy code.

In the next labs, we'll ask you to write your own tests before you even start writing code. This helps you think about the problem, and is a really great professional practice.

Finally

If you've been working in pairs, you'll both want a copy of the code. The other person should also take a fork of the codeabase and should accept a pull request for the changes, so that everyone has working labs.