Python on the command line

Data Processing in Shell

Susan Sun

Data Person

Python basics

Python

comes pre-installed on MacOS, Linux
needs to be user-install for Windows instructions here
can be used with GUI interfaces (e.g Jupyter Notebook, Spyder, PyCharm, etc.)
can also be accessed directly via the command line interface

Using Python documentation

Documentation:

man python

...
-V ,  --version 
    Prints the Python version number of the executable and exits.

python --version

Python 3.5.2

Using Python documentation

Example: using native Python

which python

/usr/bin/python

The Python interactive session

To activate a Python interactive session in the terminal:

python

Python 3.5.2 (default, Nov 23 2017, 16:37:01)
[GCC 5.4.0 20160609] on linuxType "help", "copyright", "credits" or 
"license" for more information.
>>>

The Python interactive session

Inside the interactive session, only use Python syntax:

>>> print('hello world')
hello world

To exit the Python session and return to terminal:

>>> exit()
$

Python interactive session alternative

Python interactive session:

easy to activate, intuitive
not good for code reproducibility

Alternative:

save Python commands in a Python .py script
execute script by calling python + script

Python script execution on the command line

Method 1

Create a .py file using a text editor on the command line (e.g. nano, Vim, Emacs)

Screenshot of the nano text editor in a dark Terminal window

Python script execution on the command line

Method 2

Create a .py file by echo-ing the Python syntax into the hello_world.py file, instantiating the Python file in the same step.

echo "print('hello world')" > hello_world.py

Sanity check file content:

cat hello_world.py

print('hello world')

Python script execution on the command line

Make sure in the same directory as the .py file:

ls

hello_world.py

Execute .py file by preceding filename with python:

python hello_world.py

hello world

Let's practice!

Data Processing in Shell