5. Python Script#
A Python script is essentially a list of statements entered into a text file that will be executed by the Python interpreter in the order in which they are written in the file. A key benefit of using a script is to define variables and not having to type them out every time that you want to perform a series of tasks to create a desired output in a notebook environment.
It is relatively easy to use some Python scripting to ease various tasks, including map making. During this section we will see how you can turn a notebook file into a script to make it easier to reproduce the desired output with less effort than opening a notebook file and running all of the cells.
5.1. Hello World Script#
Let’s start very simply by creating a simple Python script that prints the statement ‘Hello World!’!
Open a new file using vi by typing the following in a new terminal window:
kgoebber@bergeron:~> vi script1.py
Now add the following code to your script, save the output, and quit the file.
# Print the following statement to standard output
print('Hello World')
Once you are back at the terminal prompt we now want to run our script. To run a python script we want to run our file through the Python interpreter which we can do by typing the following in the terminal:
kgoebber@bergeron:~> python script1.py
The output should be:
Hello World!
And that’s it! You just wrote and ran your first Python script!
Now let’s develop a bit more into a simple script.
5.2. Building a full Python script#
Open a new text file from the terminal window (or the terminal from the
Jupyter Lab Launcher window) using vi (or any other text editing tool you
might know) and call it my_script.py. Once the new file is open the
first thing you will want to add some lines that describe the script and
what it does. This is called a comment block. Recall that a comment in Python
code begins with the pound (hashtag) sign (#). You may add something like
the following for your initial comment block:
############################################################
# my_script.py
# By: Kevin Goebbert
#
# This is a simple test script. It uses basic
# Python datetime commands to do a few simple
# tasks.
#
# Modifications:
#
############################################################
All of the previous is just for your information, so that you can quickly understand what you were trying to do with this particular script. Now let’s add something to the script to make it do something!
from datetime import datetime
# This is a comment and not executed
print("Hello, this is my first script.")
# Get current time from computer
now = datetime.now()
print(f"The current time is {now}")
# Get current time in UTC from computer
now_utc = datetime.utcnow()
print(f"The current time in UTC is {now_utc}")
print(f"The current month is {now_utc:%B}")
print("All done")
After you enter all of the above, write the file and quit to get back to your command prompt.
Note
Be careful with all of these quote marks. Be sure to have balance single/double quotes. If in one of the print statements we need to use nested quote marks. It doesn’t matter which is used where, just that you use different ones within the nest from what was used on the outer quote marks.
Again, recall that in order to execute a Python script, type the following on your terminal window at the command prompt
kgoebber@bergeron:~> python <yourfile>
where <yourfile> in this name that you gave to your script file (e.g.,
example_script.py). Go ahead and run the file.
What happened? Run it again, did anything change?