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Objectives

1. invoke the IPython interpreter.
2. quit the IPython interpreter.
3. navigate the IPython session history.
4. use tab-completion within IPython.
5. look up documentation in IPython.
6. interrupt incomplete or incorrect commands.

System Specifications

• Ubuntu Linux 14.04 operating system
• Python 3.5.2
• IPython 5.1.0

What is IPython

• IPython is an enhanced interactive Python interpreter.
• It provides features like tab-completion, and easier access to help.

Type ipython >> press Enter

First open the terminal by pressing Ctrl+Alt+T keys simultaneously on the keyboard.

Type ipython3 at the prompt and press Enter.

If IPython is not installed, please refer to the Instruction sheet.

Point to the version information with mouse.

The versions of Python and IPython that are installed, are shown on the terminal.

Type Ctrl+D

Press Ctrl+D keys.

Type y for yes and quit IPython.

Note that y is given in square brackets so it is default.

We could also press Enter and it will exit.

Else type n for no if you don't want to quit IPython.

Type y >> press Enter.

We have quit IPython interpreter and are back at the terminal prompt.

Type ipython >> press Enter

Type ipython3 in the terminal and press Enter.

Let us start with the simplest operation - addition.

1+2

Point at the Out[1] prompt

We press Enter to execute the python command. Please do so after typing every command.

IPython promptly displays the output as 3.

Notice that the output is shown with an Out square brackets 1 indication.

5 – 3

7 * 4

5 minus 3,

7 multiplied by 4,

Each time we press Enter and see the output on the IPython console window.

Instead of typing the whole command, we can recall the command 1 plus 2 we typed earlier.

Use the up arrow key to go back to the command 1+2.

Use left arrow to navigate to start of line

Type print (>> press space) and press Enter.

We have changed the command to print (1 plus 2). Now press Enter.

Highlight the result line.

Point at the Output

Notice that this time, the indication Out square brackets is not displayed.

Press up-arrow key

We use the up arrow key to navigate to the previous command print (1 plus 2).

Change print (1+2) to print (10*2)

As with any programming language, asterix is used for multiplication operator.

Highlight output

<<PAUSE>>

Let us consider an example.

pri<tab>

For this we just type pri at the prompt and press the tab key.

This feature of IPython is called the tab-completion.

p<tab>

Just type p and then press the tab.

This is because, there are more than one command beginning with p.

Therefore, it just lists out all the possible tab-completions of p.

Exercise 1

Pause the video, solve the problem and resume the video.

1. find out the commands starting with "ab".
2. list out the commands starting with "a".

ab<tab>

a<tab>

a tab displays a list of all the commands starting with a.

We will use the help feature of IPython to find out this.

The IPython interpreter will show the documentation for the function.

Type abs? >> press Enter

abs(-19)

abs(19)

On the console, type a b s minus 19 and then a b s 19.

We get 19, as expected, in both the cases.

abs(-10.5)

Let us try a b s minus 10.5.

We get 10.5 as the result.

Exercise 2

round?

Try out the following exercise and resume the video.

Look-up the documentation of round and see how to use it.

Type round?

Highlight the definition of round

You can look up the documentation of the function round by typing round question mark.

It says here that the function round, rounds a number to a given precision.

Highlight the syntax of ndigits

Notice, there are extra square brackets around ndigits.

This means that ndigits is optional and 0 is the default value.

Optional parameters are shown in square brackets in Python documentation.

Exercise 3

Try out the following exercise and resume the video.

Check the output of

round 2.48 round 2.48 comma 1 round 2.484 round 2.484 comma 2

Solution 3

round 2.48 is equal to 2.0 round 2.48 comma 1 is 2.5 round 2.484 is 2.0 round 2.484 comma 2 is 2.48

which are what we expect.

round(2.484

Press Enter

Let us make a typing error deliberately.

Type round open parenthesis 2.484 and press Enter, without closing the parenthesis.

Point at the prompt with three dots

This prompt is the continuation prompt of IPython.

It appears when the previous line is incomplete.

We get the expected output, that is 2.

round(1a >> press Enter

press Ctrl+C

In such case, we can press Ctrl+C keys, to interrupt the command and get back to the IPython prompt.

E.g, round takes only numbers as input. Type round(1a

Do not close the parenthesis and press Enter.

We gave alpha-numeric value '1 a' as input.

Press Ctrl+C to interrupt the execution.

Exercise 4

Try out the following exercise and resume the video.

1. Type round 2.484, without closing the parenthesis and press Enter.
2. Then cancel the command using Ctrl+C.
3. Type the command round 2.484 comma 2

round(2.484

Ctrl+C

round(2.484, 2)

Summary

In this tutorial,we have learnt to,

1. invoke the IPython interpreter by typing ipython in the terminal.
2. quit the IPython interpreter by using Ctrl+D.
3. navigate the IPython session history by using the arrow keys.
4. use the tab-completion to work faster.
5. see the documentation of functions using question mark.
6. interrupt commands using Ctrl+C when we make an error.

Assignment

1. IPython is a programming language similar to Python.True or False
   
2. Which key combination quits IPython?
   • Ctrl + C
   • Ctrl + D
   • Alt + C
   • Alt + D
     
3. Which character is used at the end of a command, in IPython to display the documentation?
   • under score
   • question mark
   • exclamation mark
   • ampersand
     

Solutions

1. False. IPython is not a new programming language. It is just an enhanced interactive Python interpreter.
2. We use Ctrl + D to quit IPython interpreter.
3. We use ? at the end of the command to display its documentation.

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