task1.md

Task 1

tomhodson.github.io/command_line_slides/task1

Making a simple python project

Decide where you'd like to put the project

First navigate somewhere we can make a temporary project, I suggest either your home directory or a subdirectory of it:

cd ~
# or
cd ~/Documents

Make a folder to hold it

We're going to write a script to print the size of files, so let's call it filesize

pwd #check you're in the right place
mkdir filesize #make a folder here called filesize

Make README.md and requirements.txt files

These files are a de facto standard to have in your python project. README.md describes your project as in written in MarkDown, which is also what this document is written in.

nano README.md

In nano, # FileSize and then CTRL-O and then ENTER to save and CTRL-X to exit.

I'll show you a differnt trick to quickly make a one line file:

echo "numpy" > requirements.txt

This uses two things I haven't told you about, echo outputs whatever you give it and > saves the output of a command to file.

Check the files contain what you think:

cat requirements.txt
cat README.md

If not you can use nano to edit them. You can also use your own text editor to do this.

Make a python script

At this point pwd should print something like /home/user/filesize/ and ls should print requirements.txt and README.md

It's a convention for python project that the actual source code goes in project_name/project_name/source_code.py So make a second folder called filesize inside the first.

Now make a python file called "filesize.py" inside it so that it ends up at filesize/filesize/filesize.py

Arrange that it contains:

import os, sys
arguments = sys.argv[1:] # The first argument is actually the name of the script
if len(arguments) == 1: print(os.path.getsize(arguments[0]))
else: print(f'filesize requires exactly one argument! Got {len(arguments)}')

Try it out

To run a python script as a command you can use

python filesize/filesize.py

To give it an argument, let's try README.md, run:

python filesize/filesize.py README.md

A recording of me doing the above, mistakes and all