Running and Quitting

Overview

Teaching: 15 min
Exercises: 0 min
Questions
  • How can I run Python programs?

Objectives
  • Launch the Jupyter Notebook, create new notebooks, and exit the Notebook.

  • Create Markdown cells in a notebook.

  • Create and run Python cells in a notebook.

Python programs are plain text files.

Use the Jupyter Notebook for editing and running Python.

Example Jupyter Notebook
Screenshot of a Jupyter Notebook on quantum mechanics by Robert Johansson

How It’s Stored

  • The notebook file is stored in a format called JSON.
  • Just like a webpage, what’s saved looks different from what you see in your browser.
  • But this format allows Jupyter to mix software (in several languages) with documentation and graphics, all in one file.

The Notebook has Command and Edit modes.

Code vs. Text

We often use the term “code” to mean “the source code of software written in a language such as Python”. A “code cell” in a Notebook is a cell that contains software; a “text cell” is one that contains ordinary prose written for human beings.

Command Vs. Edit

In the Jupyter notebook page are you currently in command or edit mode?
Switch between the modes. Use the shortcuts to generate a new cell. Use the shortcuts to delete a cell

Solution

Command mode has a grey boarder and Edit mode has a green border. Use “esc” and “Enter” to switch between modes. You need to be in command mode (Hit “esc” if your cell is green). Type “B” or “A”. You need to be in command mode (Hit “esc” if your cell is green). Type “X”.

Use the keyboard and mouse to select and edit cells.

The Notebook will turn Markdown into pretty-printed documentation.

Markdown does most of what HTML does.

*   Use asterisks
*   to create
*   bullet lists.
  • Use asterisks
  • to create
  • bullet lists.
1.  Use numbers
1.  to create
1.  numbered lists.
  1. Use numbers
  2. to create
  3. numbered lists.
*  You can use indents
	*  To create sublists 
	*  of the same type
*  Or sublists
	1. Of different
	1. types
  • You can use indents
    • To create sublists
    • of the same type
  • Or sublists
    1. Of different
    2. types
# A Level-1 Heading

A Level-1 Heading

## A Level-2 Heading (etc.)

A Level-2 Heading (etc.)

Line breaks
don't matter.

But blank lines
create new paragraphs.

Line breaks don’t matter.

But blank lines create new paragraphs.

[Create links](http://software-carpentry.org) with `[...](...)`.
Or use [named links][data_carpentry].

[data_carpentry]: http://datacarpentry.org

Create links with [...](...). Or use named links.

Creating Lists in Markdown

Create a nested list in a Markdown cell in a notebook that looks like this:

  1. Get funding.
  2. Do work.
    • Design experiment.
    • Collect data.
    • Analyze.
  3. Write up.
  4. Publish.

Solution

This challenge integrates both the numbered list and bullet list. Note that the bullet list is indented 2 spaces so that it is inline with the items of the numbered list.

1.  Get funding.
2.  Do work.
    *   Design experiment.
    *   Collect data.
    *   Analyze.
3.  Write up.
4.  Publish.

More Math

What is displayed when a Python cell in a notebook that contains several calculations is executed? For example, what happens when this cell is executed?

7 * 3
2 + 1

Solution

Python returns the output of the last calculation.

3

Change an Existing Cell from Code to Markdown

What happens if you write some Python in a code cell and then you switch it to a Markdown cell? For example, put the following in a code cell:

x = 6 * 7 + 12
print(x)

And then run it with shift+return to be sure that it works as a code cell. Now go back to the cell and use escape+M to switch the cell to Markdown and “run” it with shift+return. What happened and how might this be useful?

Solution

The Python code gets treated like markdown text. The lines appear as if they are part of one contiguous paragraph. This could be useful to temporarily turn on and off cells in notebooks that get used for multiple purposes.

x = 6 * 7 + 12 print(x)

Equations

Standard Markdown (such as we’re using for these notes) won’t render equations, but the Notebook will. Create a new Markdown cell and enter the following:

$\sum_{i=1}^{N} 2^{-i} \approx 1$

(It’s probably easier to copy and paste.) What does it display? What do you think the underscore, _, circumflex, ^, and dollar sign, $, do?

Solution

The notebook shows the equation as it would be rendered from latex equation syntax. The dollar sign, $, is used to tell markdown that the text in between is a latex equation. If you’re not familiar with latex, underscore, _, is used for subscripts and circumflex, ^, is used for superscripts. A pair of curly braces, { and }, is used to group text together so that the statement i=1 becomes the the subscript and N becomes the superscript. Similarly, -i is in curly braces to make the whole statement the superscript for 2. \sum and \approx are latex commands for “sum over” and “approximate” symbols.

Key Points

  • Python programs are plain text files.

  • Use the Jupyter Notebook for editing and running Python.

  • The Notebook has Command and Edit modes.

  • Use the keyboard and mouse to select and edit cells.

  • The Notebook will turn Markdown into pretty-printed documentation.

  • Markdown does most of what HTML does.