Python-3.4.3/C3/Dictionaries/English-timed

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Time Narration
00:01 Welcome to the spoken tutorial on Dictionaries.
00:05 In this tutorial, we will learn to,

Create dictionaries

Add and delete data from dictionaries

Retrieve data from dictionaries

Check for presence of keys and

Iterate over elements.

00:25 To record this tutorial, I am using

Ubuntu Linux 16.04 operating system

Python 3.4.3 and

IPython 5.1.0

00:40 To practise this tutorial, you should know how to

use basic data types and operators

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

00:54 First we will learn about dictionaries.
00:58 Dictionary is an unordered collection of items which has key:value pairs.

Dictionary is used to look up for a specific key and retrieve the corresponding value.

01:12 Keys are unique within a dictionary while values may not be.
01:18 The values of a dictionary can be of any data type.
01:23 But the keys must be of immutable data type such as strings, numbers or tuples.
01:31 Let us start ipython. Open the terminal.
01:37 Type ipython3 and press Enter. From here onwards, remember to press the Enter key after typing every command on the terminal.
01:50 Let us start by creating an empty dictionary.
01:54 Type, empty is equal to open and close curly braces Note that unlike lists, curly braces are used to define a dictionary.
02:06 Now let us see how to create a non empty dictionary.
02:11 Type as shown. Note that,

Each key:value pair is separated by a comma,

Each key is separated from its value by a colon, and

The whole thing is enclosed in curly braces.

02:29 Here, we have defined four entries in the dictionary student. The keys are name, age, gender, class.
02:44 Type, student to see its content.
02:50 Next let us learn to access the dictionary elements.
02:55 The value of a dictionary can be accessed using the corresponding key.
03:01 The syntax is: dictionary underscore name inside square brackets key
03:07 Now let us access the value for the key ‘name’.
03:12 Type, print inside brackets student inside square brackets inside single quotes name
03:21 As expected it printed the output as raj.
03:26 Now we will retrieve the value for the key ‘class’
03:31 Type, print inside brackets student inside square brackets inside single quotes class

It displays the output as 10.

03:43 If we try to access a value with a wrong key, we get an error.
03:49 Type, student inside square brackets inside single quotes height
03:56 The interpreter gave us the KeyError: 'height' This is because, key 'height' is not present in the student dictionary.
04:05 This is about creating dictionaries.
04:09 Next, let us see how to add or delete items in a dictionary.
04:15 First let us add an element height to the dictionary student.

Type, student inside square brackets inside single quotes height is equal to 6.2

04:29 Let us now check the content of the dictionary.

Type, student You can see that key-value 'height': 6.2 is added to the dictionary student.

04:42 Next let us modify the element class of the dictionary student.

Type, student inside square brackets inside single quotes class is equal to 11

04:56 Now, to check the content of the dictionary, type, student
05:02 As you can see, the value for class key is changed to 11 .
05:06 Next let us learn to delete age from the dictionary student.

Type, del student inside square brackets inside single quotes age

05:20 Type, student You can see that now key-value 'age': 16 is deleted from student.
05:29 Next let us see how to check whether a key is present in a dictionary.

For that we can use the method in.

05:39 The method in will return True if the key is found in the dictionary. It will return False if key is not present.
05:48 Note that we can check only for the presence of the keys in dictionaries and not values.
05:55 Keys of a dictionary are not ordered. Hence, slicing and striding are not valid on dictionaries.
06:03 Let us try it with an example.
06:06 Type, inside single quotes school in student We get False, since the key 'school' is not present in student.
06:17 Type, inside single quotes name in student We get True, as expected.
06:25 Next let us see how to retrieve keys and values of a dictionary.

Method keys() is used for getting a list of keys

Method values() is used for getting a list of values.

06:40 Now let us try the above methods with examples. Type, student dot keys open and close brackets It returns the list of keys of the dictionary student.
06:56 Type, student dot values open and close brackets

It returns the list of values of the dictionary student.

07:07 Next let us see the items method.

Type, student dot items open and close brackets

07:16 It returns a list of tuples of key-value pairs of the dictionary student.
07:22 The order of items of the list returned by keys(), values() and items() cannot be predicted.
07:30 In dictionaries, they are not in the order in which we inserted them.
07:35 Pause the video. Try this exercise and then resume the video.
07:41 Print the keys and values of the dictionary student one by one. Hint: use the method items and for loop.
07:50 Switch back to the terminal for the solution.
07:54 Type as shown. It displays the keys and values one by one.
08:02 This brings us to the end of this tutorial. Let us summarize.
08:08 In this tutorial, we have learnt to,

Create dictionaries

Access elements of a dictionary using keys

Add elements to a dictionary by assigning a value to a key

08:22 Delete elements from a dictionary by using the function del

Retrieve the keys and values by using the methods keys() and values() respectively

08:34 and Iterate over elements of a dictionary using a for loop.
08:39 Here are some self assessment questions for you to solve

Dictionary d is defined as shown:

How do you retrieve the value 'b'?

Delete value 'b' from the dictionary d

08:55 And the answers,

d inside square brackets 2 gives the value 'b'

del d inside square brackets 2 deletes the value ‘b’

09:10 Please post your timed queries in this forum.
09:14 Please post your general queries on Python in this forum.
09:19 FOSSEE team coordinates the TBC project.
09:23 Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India. For more details, visit this website.
09:34 This is Priya from IIT Bombay, signing off. Thanks for watching.

Contributors and Content Editors

Pratik kamble