Difference between revisions of "Python-3.4.3/C3/Sequence-datatypes/English"

Objectives

• Sequence Data types such as
  • List
  • String and
  • Tuple
• Accessing the above data types using index
• Convert list to tuple and vice-versa and
• Convert string to list and vice-versa.

System Specifications

• Ubuntu Linux 16.04 operating system
• Python 3.4.3 and
• IPython 5.1.0

Pre-requisite slide

• run basic Python commands on the ipython console

If not, see the relevant Python tutorials on this website.

Sequence data types

The elements are accessed using index numbers.

The sequence data types in Python are

• list
• string and
• tuple

Lists

List is a container that holds a number of objects in the given order.

For example: num underscore list is equal to inside square brackets 1, 2, 3, 4

A list can store data of any type.

List is most useful when storing data of identical type.

Examples:

• Name of books in a library and
• Passengers on a flight

Type, ipython3 --pylab

press Enter

Open the terminal.

Type ipython3 space hyphen hyphen pylab and press Enter.

From here onwards, remember to press the Enter key after typing every command on the terminal.

Type, num underscore list is equal to inside square brackets 1, 2, 3, 4

Highlight [1, 2, 3, 4]

Comma-separated items enclosed in square brackets constitute a list.

Type, var underscore list is equal to inside square brackets 1, 1.2, inside square brackets 1,2

Type greeting underscore string is equal to inside double quotes hello

It is now a string variable with the value hello.

k is equal to inside single quotes Single quote

Highlight the quotes

Here single, double and triple quotes are used as delimiters.

Highlight (17,"Ram",56.8)

Highlight (

Type person underscore tuple is equal to inside brackets 17, inside double quotes Ram, 56.8

This tuple contains age,name and weight of a person.

To create a tuple we use normal brackets unlike square brackets for list.

<<PAUSE>>

Type, num underscore list inside square brackets 2

Recall that, the index of the elements starts with 0 instead of 1.

Type, greeting underscore string inside square brackets 1

Highlight the outputs

We can see that the output is displayed as per the index value.

Type person underscore tuple inside square brackets 2

Highlight the outputs

The output shows the weight and age of the person as per the index value.

<<PAUSE>>

Highlight the output

Type num underscore list plus var underscore list

Addition gives a new sequence containing both the sequences.

Type a underscore string is equal to inside double quotes <space> another string

Highlight the output

We can see that both the strings are added now.

Highlight comma

Type, t2 is equal to inside brackets inside double quotes Student comma

Adding a comma after Student is important to make t2 a tuple.

Highlight student

Now we can see that Student is added to the tuple.

We use len function for that.

Type, len inside brackets num underscore list

The output shows the number of objects of the list.

Type, 3 in num underscore list

We can see that the output displays True and False accordingly.

We use max function to find the maximum value.

Type, max inside brackets num underscore list

Type, min inside brackets greeting underscore string

For string data type, ASCII value is used to get the maximum and minimum values.

Type, sum inside brackets num underscore list

<<PAUSE>>

But there are many important features in list that differ from string and tuple.

Let us see them using some examples.

Type, num underscore list inside square brackets 1 is equal to 9

Highlight the output

Here the value at index 1 is assigned to 9.

Highlight the error

The first command executes without a problem.

But there is an error in the second one.

Highlight the error

Type person underscore tuple inside square brackets 0 is equal to 23

We can see the same error again.

This is because strings and tuples share the property of being immutable.

We cannot change the value at a particular index.

But we can convert list to tuple and tuple to list.

<<PAUSE>>

Type as shown

Tuple function converts the list to tuple.

Highlight the brackets

Now the list is successfully converted to tuple.

Type as shown.

List function converts the tuple to list.

Highlight the square brackets

Now the tuple is successfully converted to list.

Let us say we have the following string.

Highlight the output

This produces a list with the string split at comma.

It joins a list to make a string.

Let us say we have the following list.

Highlight the output

Thus we get a list joined on commas.

Highlight the string

Type as shown.

Note that the list has to be a list of strings to apply join operation.

Highlight the output

We can see that the list is joined on spaces.

<<PAUSE>>

Exercise 1

Try this exercise and then resume the video.

Check if 3 is an element of the following list.

Change the third element in the list to 21.

The output is True. So the element 3 is in the list.

Highlight 21

We can see that the element 3 is changed to 21.

Exercise 2

Try this exercise and then resume the video.

Convert the string "Elizabeth is queen of england" to "Elizabeth is queen"

Highlight the output

We got the required output.

Summary slide

In this tutorial, we have learnt to,

• Use the sequence data types such as List, String and Tuple
• Split and join a list using split and join functions respectively
• Convert list to tuple and vice-versa and
• Convert string to tuple and vice-versa

Evaluation

1. What is the major difference between tuple and list?
2. Split the below string on whitespaces

Solutions

1. The major difference between tuple and list is that,

• Tuple is immutable while list is not
• Tuple is used to store data related to an item
• But list is typically used to store items of identical type

2. To split the string on whitespace, we use the split function without any argument

For more details, visit this website.

Thanks for watching.