Pravin1389: Created page with '{| border=1 !Visual Cue !Narration |- | Show Slide 1 Containing title, name of the production team along with the logo of MHRD | Hello friends and Welcome to the spoken tutori…'

2012-12-02T10:16:25Z

Created page with '{| border=1 !Visual Cue !Narration |- | Show Slide 1 Containing title, name of the production team along with the logo of MHRD | Hello friends and Welcome to the spoken tutori…'

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{| border=1
!Visual Cue
!Narration
|-
| Show Slide 1

Containing title, name of the production team along with the logo of MHRD
| Hello friends and Welcome to the spoken tutorial on 'dictionaries'.

|-
| Show Slide 2

Learning objectives
| At the end of this tutorial, you will be able to,

# Create dictionaries.
# Add and delete data from dictionaries.
# Retrieve data from dictionaries.
# Check for container-ship of keys.
# Iterate over elements.

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| Show Slide 3

Pre-requisite slide
| Before beginning this tutorial,we would suggest you to complete the tutorial on "Basic datatypes and operators".

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| Show Slide 4

Overview of dictionaries
| A dictionary in general, is designed to look up for meanings of words. Similarly, Python dictionary is also designed to look up for a specific key and retrieve the corresponding value. Dictionaries are data structures that provide key-value mappings. Dictionaries are similar to lists except that instead of the values having integer indexes, dictionaries have keys or strings as indexes.

|-
| Open the terminal

ipython
| We start our ipython interpreter as,

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| mt_dict = {}
| Let us start by creating an empty dictionary. Type the following in your IPython interpreter.

|-
| move the mouse over curly braces
| Notice that unlike lists, curly braces are used to define a <tt>dictionary</tt>.

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| extensions = {'jpg' : 'JPEG Image', 'py' : 'Python script',
'html' : 'Html document', 'pdf' : 'Portable Document Format'}
| Now let us see how to create a non-empty dictionary,

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| Move the mouse over the commas
| Notice that each key-value pair is separated by a comma.

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| Move the mouse over the colon one by one
| and each key and value are separated using a colon.

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| extensions
| Here, we have defined four entries in the dictionary extensions. The keys are

jpg, py, html, and pdf.

Simply type,extensions in the interpreter to see the content of the dictionary.

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| Show Slide 5

Accessing elements
| Notice that, in dictionaries, the order cannot be predicted and you can see that the values are not in the order that we entered in.

|-
| Switch to terminal

<nowiki>print extensions['jpg']</nowiki>
| Like in lists, the elements in a dictionary can be accessed using the index, here the index is the key. We type,

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| <nowiki>print extensions['zip']</nowiki>
| It printed JPEG Image. And now try,

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| <nowiki>extensions['cpp'] = 'C++ code'</nowiki>
| Well it gave us an error, saying that the key 'zip' is not in the dictionary.

<nowiki>Pause here for some time and try few more keys. Also try jpg in capital letters. <continue from paused state> Well that was about creating dictionaries, now how do we add or delete items. We can add new items into dictionaries as,</nowiki>

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| <nowiki>del extensions['pdf']</nowiki>
| and delete items using the <tt>del</tt> keyword as,

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| extensions
| Let us check the content of the dictionary now,

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| <nowiki>extensions['cpp'] = 'C++ source code'</nowiki>
extensions
| So the changes have been made. Now let us try one more thing,

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| 'py' in extensions
'odt' in extensions
| As you can see, it neither added a new thing nor gave an error, but it simply replaced the existing value with the new one.

Now let us learn how to check if a particular key is present in the dictionary. For that we can use the method <tt>in</tt>,

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| Show Slide 6

Retrieve keys and values
| It will return <tt>True</tt> if the key is found in the dictionary, and will return <tt>False</tt> if key is not present. Note that we can check only for container-ship of keys in dictionaries and not values.

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|
| Now let us see how to retrieve the keys and values. We can use the method <tt>keys()</tt> for getting a list of the keys in a particular dictionary and the method <tt>values()</tt> for getting a list of values.

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| Switch to terminal

extensions.keys()
| Let us try them,

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| extensions.values()
| It returned the <tt>list</tt> of keys in the dictionary extensions. And now the other one,

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|
| It returned the <tt>list</tt> of values in the dictionary.

Pause the video here, try out the following exercise and resume the video.

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| Show Slide 7

Assignment 1
| Print the keys and values in the dictionary one by one.

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| Continue from paused state Switch to the terminal

for each in extensions.keys():
<nowiki>print each, "-->", extensions[each]</nowiki>
| Switch to terminal for solution.

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| Show Slide 8

Summary slide
| This brings us to the end of this tutorial. In this tutorial, we have learnt to,

# Create dictionaries namely -- - empty dictionaries - dictionaries with data.
# Access elements in the dictionaries using the keys.
# Add elements to a dictionary by assigning a value to a key.
# Delete elements from a dictionary by using the function <tt>del</tt>.
# Retrieve the keys and values by using the methods <tt>.keys()</tt> and <tt>.values()</tt> respectively.
# Iterate over elements of a dictionary using a <tt>for</tt> loop.

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| Show Slide 9

Self assessment questions slide
| Here are some self assessment questions for you to solve

# Container-ship of values can be checked in a python dictionary
** True
** False
# Consider the python dictionary <tt>x = {'a' : <nowiki>['a','b','c'], 'b' : (1, 2, 3), 1 : {1 : 'one', 2 : 'two'}, 10 : {10 : 'ten', 11 : </nowiki>'eleven'}}</tt>. What will the following code return?<br/> Unexpected indentation.<br/> <tt>(1, 2, 3) in x.values()</tt>.
** True
** False
** Container-ship of values cannot be checked in dictionaries
** The dictionary is invalid

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| Show Slide 10

Solution of self assessment questions on slide
| And the answers,

# False. Container-ship of only keys can be checked in a python dictionary.
# True

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| Show Slide 11

Acknowledgment slide
| Hope you have enjoyed this tutorial and found it useful. Thank you!

|}

Python/C3/Dictionaries/English - Revision history

Pravin1389: Created page with '{| border=1 !Visual Cue !Narration |- | Show Slide 1 Containing title, name of the production team along with the logo of MHRD | Hello friends and Welcome to the spoken tutori…'