Working with code cells

In this notebook you'll get some experience working with code cells.

First, run the cell below. As I mentioned before, you can run the cell by selecting it the click the "run cell" button above. However, it's easier to run it by pressing Shift + Enter so you don't have to take your hands away from the keyboard.

Shift + Enter runs the cell then selects the next cell or creates a new one if necessary. You can run a cell without changing the selected cell by pressing Control + Enter.

The output shows up below the cell. It's printing out the result just like in a normal Python shell. Only the very last result in a cell will be printed though. Otherwise, you'll need to use print() print out any variables.

Exercise: Run the next two cells to test this out. Think about what you expect to happen, then try it.

Now try assigning a value to a variable.

There is no output, 'growth' has been assigned to the variable mindset. All variables, functions, and classes created in a cell are available in every other cell in the notebook.

What do you think the output will be when you run the next cell? Feel free to play around with this a bit to get used to how it works.

Code completion

When you're writing code, you'll often be using a variable or function often and can save time by using code completion. That is, you only need to type part of the name, then press tab.

Exercise: Place the cursor at the end of mind in the next cell and press tab

Here, completing mind writes out the full variable name mindset. If there are multiple names that start the same, you'll get a menu, see below.

Remember that variables assigned in one cell are available in all cells. This includes cells that you've previously run and cells that are above where the variable was assigned. Try doing the code completion on the cell third up from here.

Code completion also comes in handy if you're using a module but don't quite remember which function you're looking for or what the available functions are. I'll show you how this works with the random module. This module provides functions for generating random numbers, often useful for making fake data or picking random items from lists.

Exercise: In the cell below, place the cursor after random. then press tab to bring up the code completion menu for the module. Choose random.randint from the list, you can move through the menu with the up and down arrow keys.

Above you should have seen all the functions available from the random module. Maybe you're looking to draw random numbers from a Gaussian distribution, also known as the normal distribution or the "bell curve".

Tooltips

You see there is the function random.gauss but how do you use it? You could check out the documentation, or just look up the documentation in the notebook itself.

Exercise: In the cell below, place the cursor after random.gauss the press shift + tab to bring up the tooltip.

You should have seen some simple documentation like this:

Signature: random.gauss(mu, sigma)
Docstring:
Gaussian distribution.

The function takes two arguments, mu and sigma. These are the standard symbols for the mean and the standard deviation, respectively, of the Gaussian distribution. Maybe you're not familiar with this though, and you need to know what the parameters actually mean. This will happen often, you'll find some function, but you need more information. You can show more information by pressing shift + tab twice.

Exercise: In the cell below, show the full help documentation by pressing shift + tab twice.

You should see more help text like this:

mu is the mean, and sigma is the standard deviation.  This is
slightly faster than the normalvariate() function.