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This page guides you how to use Python and Jupyter Notebook using the example, Celsius and Fahrenheit converter.

When you want to convert the unit from Fahrenheit to Celsius, the formula is:

$T[^{\circ}C] = (T[^{\circ}F] - 32) \times 5/9$

From Celsius to Fahrenheit, the formula is:

$T(^{\circ}F) = (T[^{\circ}C] \times 9/5) + 32$

Python

To start Python, you can type python in the terminal.

$ python

Then you may see that the prompt has been changed as

Python 3.6.3 |Anaconda, Inc.| (default, Oct  6 2017, 12:04:38)
[GCC 4.2.1 Compatible Clang 4.0.1 (tags/RELEASE_401/final)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>

Ask for the input in Celsius:

>>> TinC = int(input("Enter a temperature in Celsius: "))

Then you can see the next line asking a temperature in Celsius.

Enter a temperature in Celsius:

We can say 30, although you can give any number. Then TinC carries 30. Next is to convert temperature from Celsius to Fahrenheit using the formula.

>>> TinF = 9.0/5.0 * TinC + 32

It is time to print out the answer.

>>> print("Temperature:", TinC, "degC = ", TinF, "degF")

This should give you

Temperature: 30 degC =  86.0 degF

Once you are done, you can exit Python by typing quit()

>>> quit()

Make the unit converter from Fahrenheit to Celsius by yourself.

IPython

Interactive Python (IPython) gives you more functionality by providing a wider range of commands than python. To launch IPython, simply type

$ ipython

This will give you

Python 3.6.3 |Anaconda, Inc.| (default, Oct  6 2017, 12:04:38)
Type 'copyright', 'credits' or 'license' for more information
IPython 6.1.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]:

Here, you can follow the same procedure as in python to have the program of the unit converter.

In [1]: TinC = int(input("Enter a temperature in Celsius: "))
Enter a temperature in Celsius: 30

In [2]: TinF = 9.0/5.0 * TinC + 32

In [3]: print("Temperature:", TinC, "degC = ", TinF, "degF")
Temperature: 30 degC =  86.0 degF

As already mentioned above, IPython provides useful functions. For example, if you want to know about the command input, you can type

In [4]: input?

If you want to know what variables are defined, type

In [5]: whos
Variable   Type     Data/Info
-----------------------------
TinC       int      30
TinF       float    86.0

IPython also provides many magic functions. The built-in magics include:

Functions that work with code: %run, %edit, %save, %macro, %recall, etc.
Functions which affect the shell: %colors, %xmode, %autoindent, %automagic, etc.
Other functions such as %reset, %timeit, %%writefile, %load, or %paste.

You can always call them using the % prefix, and if you’re calling a line magic on a line by itself, you can omit %. For more information about built-in magic commands, please refer to IPython webpage

To exit IPython, you can do either quit or exit.

Python script

If the job requires more than a few lines of python codes, then typing commands can be overwhelming. Also, it is likely that you make mistakes. In this case, writing all python commands in a python script and running this script to get the result is the way to go.

The first thing to do is create a python script file using text editors. If you use vim, you can easily create a file by typing vim filename.py.

$ vim ctof.py

Then write all python codes there.

# This script converts temperature in Celsius to temperature in Fahrenheit.
#
# 2018.9.13

TinC = int(input("Enter a temperature in Celsius: "))

TinF = 9.0/5.0 * TinC + 32
print("Temperature:", TinC, "degC = ", TinF, "degF")

In this example, the first three lines start with #. Whenever a line starts with #, python just skips it. So it is useful to add an explanation of your code in the script file.

You can execute this script in a few different ways.

1. In Python

After launching python, you can execute your python script as follows.

>>> exec(open('ctof.py').read())

If you input temperature in Celsius when it asks temperature, you can get the result.

Enter a temperature in Celsius: 30
Temperature: 30 degC =  86.0 degF

If you think that this is not a really convenient way to run the program, there are alternative ways.

2. In IPython

Running a python script in IPython is much easier than in Python. After launching IPython with ipython, you can just type

In [1]: %run ctof.py

to get the same result as in python. You can even drop the file extension.

In [2]: %run ctof

even just run ctof.py or run ctof will do the job!

Another way to run the script, copy whole lines and paste them in IPython. To paste copied lines in IPython, you can use a magic function %paste.

In [3]: %paste

Then IPython shows the copied lines below. This is particularly useful if you need to run a few lines of your python script.

IPython allows you to open the text file with an exclamation mark (!) while you are in IPython.

In [5]: !vim ctof.py

This makes %paste really useful because you can open your script and get the necessary lines without leaving IPython.

3. Using Python in the terminal

You do not launch python to execute python scripts. In the terminal, you can run your script by

$ python ctof.py

4. As stand-alone in the terminal

If your script starts with

#!/usr/bin/env python3

you can run this script without typing python in the terminal. When you save the script, make sure to change file modes to be executable.

$ chmod 755 ctof.py

To run this executable file,

$ ./ctof.py

Jupyter Notebook

You can use Jupyter Notebook for running python commands or a script. First, launch Jupyter Notebook.

$ jupyter notebook

Then you get to have a new window in your web browser showing the file system in the working directory. To start python, click new in the upper right corner and select Python 3. This will open a new tab that just looks like IPython.

Jupyter Notebook consists of cells. It is your choice how to compose the cell with your commands. You can add all the lines in one cell, or a simple line for each cell.

Let’s first copy all the lines in a single cell. Jupyter Notebook provides a help page, and it says that you can hit control key and enter key together to run the cell. When you run the cell, you are asked to give temperature in Celsius as before.

If we decide to use cells for each line, you will be asked to give temperature after run the cell with TinC = int(input("Enter a temperature in Celsius: ")).

Once you are done, you can save the Jupyter Notebook file in the web browser.

To finish Jupyter Notebook, you can come back to the terminal where you typed jupyter notebook and hit ^C TWICE!

In the class, we can explore what Jupyter Notebook offers extensively.

Launch Jupyter Notebook remotely

In some cases, you need to use a remote server for Jupyter Notebook. In the remote server,

$ jupyter notebook --no-browser --port=8889

This launches Jupyter Notebook without opening web browser. Then on your local machine,

$ ssh -N -f -L localhost:8899:localhost:8889 [accountname]@[servername]

and open the browser and go to http://localhost:8899 The web browser ask for the key, and you can find it in the terminal where you launch Jupyter Notebook.