Running and Quitting

Overview

Teaching: 15 min
Exercises: 0 min

Questions

• How can I run Python programs?

Objectives

• Launch the Python shell.

• Launch the IPython shell.

• Launch IDLE in interactive mode.

• Launch IDLE, create a Python script, and run it.

Setup

• Obtain an interactive session on the HPC cluster:

  qsub -X -I -q training -l walltime=8:00:00 -l ncpus=1 -l mem=1G
  

• Once you’re in, load the latest Python 3 environment:

  module load python/3.6.1
  

Evaluate Python statements interactively

With vanilla Python shell

• Type python to invoke the Python shell. This is also known as a “Read-Evaluate-Print Loop” or REPL.
• Type the following statements:

  print("hi there!")
  2 + 2
  exit()
  

With enhanced IPython shell

• Type ipython to invoke IPython, an ‘‘enhanced’’ interactive shell.
• Repeat the statements above.
• ipython interprets Python statements exactly the same way as the python REPL.
• It has some additional useful features, like code completion, syntax highlighting, and “magic” commands that begin with the ‘%’ character — type %magic to see a list of them.

With IDLE

• Type idle to invoke the Python Integrated Development and Learning Environment in interactive (shell) mode.
• Repeat the statements above.

Python programs are plain text files.

• They have the .py extension to let everyone (including the operating system) know it is a Python program. This is convention, not a requirement.
• It’s common to write them using a text editor but we are going to use IDLE
• IDLE is an example of an Interactive Development Environment, or IDE, that provides code completion and other helpful features.

Use IDLE for editing and running Python.

• Type idle my_script.py to invoke IDLE in edit mode.
• This will start IDLE as an editor, with my_script.py as the open file.
• Paste the same three commands into the editor.
• In the File menu, select Save (or Ctrl+S)
• In the Run menu, select Run Module (or F5)

Key Points

• python, ipython and idle commands all give an interactive Python shell (REPL).

• Python programs are plain text files.

• You can use IDLE for creating and running Python programs.