Script Files
Until now we have just entered commands into interpreter
To write a longer program need to write a program file or script
- Text file with Python commands that is run through the interpreter
- Extension is 'py', as in 'filename.py'
We will look at a few ways of writing and running scripts
Note: The method of running scripts is very platform specific
- This lecture is based on Python within Linux
- But still worth a quick read if you're using Windows or Mac
- If you are using Windows:
- For Python(x,y), see the documentation or Google for help
- These videos might be useful
Writing a Program
Here is a demo with Geany (because it's simple)
Let's open Geany:
Now I write my script/program in Geany
And save it as test.py in my home directory, called /home/john
(Will look different on Windows/Mac)
Notice that Geany now knows its a Python file because of the .py extension
Geany applies syntax highlighting
We've now created a file containing Python commands, stored on the hard disk
The next step is to run it
Running Scripts from the Command Line
One method is to run it from the command line (or shell in UNIX/Linux)
- Windows users can probably skip this section
Here I'm running it on Ubuntu Linux, through the shell
Better to use the -i flag to stay in Python when it finishes
- So variables are not lost
Generally, the command line method is not the best one for scientific programming
Let's look at some other ways
Running Scripts with IDLE
A very easy way to run scripts is with IDLE
- Fine to start, probably came together with your Python installation
- If you can't find it, try a search of your hard disk
- But not very high quality
- Eventually you should learn to use IPython (see below)
After starting IDLE, the first window is the Python shell (interpreter)
Go to the file menu
Yes, I know the fonts are ugly...
Select "New Window" to get a window like this:
This window serves as a text editor where we can write our program:
- Make sure you reproduce it exactly
Before running the file we need to save it
Select "Save As" from the "File" menu
You should get a dialogue box like this (Might look different on Windows/Mac)
Make sure you save it somewhere sensible, where you can find it again
Now that it's saved we can run it
Select "Run Module" from the "Run" menu
- Or just press F5
The output is sent to the Python Shell
Running Scripts with IPython
After you get comfortable, switch to IPython
- An enhanced interface to the Python interpreter
- Requires text editor to write the file (plus IPython to run it)
- Needs to be installed separately
Videos on installing and using IPython can be found here
Here's a very quick tutorial using screenshots from my Linux machine
First we fire up IPython
The next step is to run our file test.py in /home/john
The output is displayed in IPython
The only problem you might have is that test.py is not in IPython's current working directory
Error message looks like this
Let's check what directory we are in
'pwd' stands for "present working directory"
- This is a UNIX command
- Might be different according to your OS
- Might need to prepend with % as in '%pwd'
- Depends on whether 'automagic' is on or off
We are in /tmp, and the file is in /home/john
So I change to /home/john
'cd' stands for "change directory"
- See comments for 'pwd'
Now it runs okay
Things will be different with Windows or Mac
- I leave the details to you
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