Notice that we didn’t use aprint()statement, but Jupyter Notebook wrote the result anyhow.

Jupyter Notebook will only write the result of the last line but will print anything contained in a print statement no matter where it occurs. This can be confusing at first, so let’s look at an example. In the next cell, enter:

x + yx - y
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x + yx - y

notebook showing output of x + y not being displayed

This time only-1was returned. This is because Jupyter Notebook only displays the last line. If you want to display both, you have to wrap the first one in aprint()statement.

print(x + y)x - y
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print(x + y)x - y

notebook showing x + y = 5 printing and output

Try printing both lines on your own.

Let’s work with some more complicated code. The purpose of this section is to try out some basic Jupyter Notebook features. If we use a function that you have not learned about yet, don’t worry, this section is only an example.

Let’s work with some data. We have a list of numbers:mynums = [1, 2, 3, 4, 5]

Input this list into a cell and return the output.

mynums = [1, 2, 3, 4, 5]mynums
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mynums = [1, 2, 3, 4, 5]mynums

mynums listed in a notebook cell

Now let’s try printing each item to the console.

for n in mynums:    print(n+1)
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for n in mynums:    print(n+1)

for n in mynums: print(n+1) loop displayed in a notebook cell with the output displayed below the cell

Congratulations!! You are ready to start working with data in Jupyter Notebook.

The remainder of this article will introduce debugging and accessing documentation. You don’t need to know about these to start using Jupyter Notebook on your own. However, these features will support you on your learning journey (and beyond).

Jupyter Notebook has lots of built-in tools to help you learn to code. We will explore three of them here (the help documentation with?, tab completion, and how to access the function arguments). This is just the beginning, check out this section of thePython Data Science Handbookfor more tools.

Jupyter Notebook has a generalized help function with the?character. Let’s say you want to know what object typemynumsis. You can use the?to get full documentation about it.

mynums?
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mynums?

help '?' character used on mynums in a notebook cell, shows that mynums is a list with 5 objects

Here you can see the object type, a preview of the data, and general information. You can do the same for functions such aslenorsum. Go ahead and try it in your own Notebook.

Jupyter Notebook also offers tab completion. Tab completion means that you can start typing, hit theTabkey, and Jupyter Notebook will offer suggestions about what could come next. For example, to turn our list into apandasDataFrame, we can use the.DataFrame()function. But you might forget how it is spelled (i.e., is it ‘f’ or ‘F’?). The tab function to the rescue! Let’s try it out.

First, import pandas.

import pandas as pd
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import pandas as pd

Then typeDand hit theTabbutton to see your options.

pd.D
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pd.D

tab completion showing pd.D and DataFrame, DataOffset, DatetimeIndex, and DatetimeTZDtype options

You can keep typing or selectDataFramefrom the list. Now let’s finish our function:

pd.DataFrame(mynums)
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pd.DataFrame(mynums)

That’s great, but sometimes you might know the function’s name but forget what arguments it needs.

Fortunately, Jupyter Notebook has a solution for that too. For example, you want to sort your list from largest to smallest. You know you need the.sort()function, but you forgot what arguments you need to call. Place your cursor between the( )and hit theShift+Tabkeys.

mynums.sort()
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mynums.sort()

docstring for the .sort() function, shows that .sort() takes an optional reverse=True argument

That’s right! Specify reverse = True. Go ahead and try it out. Remember to call your list at the end of the cell so you can see the output.

mynums.sort(reverse=True)mynums
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mynums.sort(reverse=True)mynums

reverse sorted list displays the mynums list sorted in reverse

Great job! As you code more, some functions will become second nature, but it can be helpful to know how to find the documentation until then.

Let’s move on to one more supportive feature in Jupyter Notebook: debugging.

Now let’s try to create an error. There is no package named ‘panda’, but it is an easy typo to make. Let’s make that typo to see how Jupyter Notebook handles errors.

import panda as pd

As expected, we got an error. Jupyter Notebook tries to be as helpful as possible. There is a lot of information in this message, let’s break it down starting at the bottom. Our bottom line says:

ModuleNotFoundError: No module named 'panda'

module not found error showing “ModuleNotFoundError: No module named 'panda'” and “----> 1 import panda as pd”

Great! This error was easy to understand - “panda” doesn’t exist. If we look above our error message, we see that Jupyter Notebook also shows where this error occurred.

----> 1 import panda as pd

Sometimes the errors are more complicated, and you may not understand what they are saying. In that case, it can be helpful to copy the last line of the error and go to the internet for help.

Let’s try another example with a “magic command.” Magic commands are a group of special commands that help with a variety of non-coding tasks. For a complete list of the IPython magic commands,check out the documentation.

First, create a more complicated error:

x = 1+1y = 1-1z = x/y
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x = 1+1y = 1-1z = x/y

You should get aZeroDivisionError.

notebook showing zero division error

We want to debug this. In the next cell, type%debug. A dialog box will appear that will let you inspect your code without creating new cells. Anything you write here willnotbe saved in your notebook.

notebook debug interface with an empty ipdb> cell

A reminder of what did not work appears below. You can start by checking on each of those variables to figure out which one is causing a zero division error. In theipdb>cell, inspectxby typingx.

debug interface with x in debug field to evaluate x

Looks likex = 2, so that isn’t the problem. Tryyon your own.

The response should be0. Great! We found our bug. Now we need to close the debug cell and get back to our program. To get out of debug mode, typeexit()in theipdb>cell.

debig interface showing exit() debug to exit

Congratulations! You are now ready to write, run, and debug your own programs in Jupyter Notebook.

This is just the beginning of the functions that Jupyter Notebook has to offer. For many more helpful tools and features, check outthe documentation, and if you want to be inspired to do more with Jupyter notebook, check outA gallery of interesting Jupyter Notebooks.

Have fun coding with Jupyter Notebook!

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