Difference between revisions of "Python/C3/Dictionaries/English-timed"
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Revision as of 12:23, 28 March 2013
| Timing | Narration |
|---|---|
| 0:01 | Hello friends and Welcome to the spoken tutorial on 'dictionaries'. |
| 0:05 | At the end of this tutorial, you will be able to,
|
| 0:20 | Before beginning this tutorial,we would suggest you to complete the tutorial on "Basic datatypes and operators". |
| 0:27 | A dictionary in general, is designed to look up for meanings of words. |
| 0:35 | Similarly, Python dictionary is also designed to look up for a specific key and retrieve the corresponding value. |
| 0:43 | Dictionaries are data structures that provide key-value mappings. |
| 0:47 | Dictionaries are similar to lists except that instead of the values having integer indexes, dictionaries have keys or strings as indexes. |
| 0:58 | We start our ipython interpreter as, ipython |
| 1:07 | Let us start by creating an empty dictionary. |
| 1:12 | Type the following in your IPython interpreter,mt underscore dict = closing curly brackets |
| 1:25 | Notice that unlike lists, curly braces are used to define a dictionary |
| 1:33 | Now let us see how to create a non-empty dictionary, |
| 1:37 | so type extensions = open curly brackets in single quotes jpg colon 'JPEG Image' comma 'py' colon 'Python script' comma
'html' colon 'Html document' comma pdf colon Portable Document Format close curly brackets
|
| 2:08 | Notice that each key-value pair is separated by a comma. |
| 2:17 | and each key and value are separated using a colon. |
| 2:23 | Here, we have defined four entries in the dictionary extensions. |
| 2:29 | The keys are jpg comma py comma html comma and pdf. |
| 2:36 | Simply type,extensions in the interpreter to see the content of the dictionary. |
| 2:40 | So type extensions. |
| 2:45 | 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. |
| 2:53 | Like lists, the elements in a dictionary can be accessed using the index, here the index is the key. |
| 3:06 | We type, print extensions within closing brackets and single quotes jpg. |
| 3:25 | It printed JPEG Image. And now type print extensions within square brackets zip. |
| 3:42 | Well it gave us an error, saying that the key 'zip' is not in the dictionary. |
| 3:48 | So Pause here for some time and try few more keys. |
| 3:52 | Also try jpg in capital letters. |
| 3:58 | <continue from paused state> Well that was about creating dictionaries, now how do we add or delete items. |
| 4:09 | We can add new items into dictionaries as, |
| 4:13 | Type extensions within square brackets and single quotes cpp is equal to in single quotes C++ then code. |
| 4:36 | and delete items using the del keyword as, type del space extensions within square brackets and single quotes pdf. |
| 4:51 | Let us check the content of the dictionary now, |
| 4:54 | So type extensions. |
| 4:57 | So the changes have been made. |
| 4:59 | Now let us try one more thing, type extensions within square brackets and in single quotes cpp is equal to in single quote C++ and source code. then type again extensions. |
| 5:21 | 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. |
| 5:29 | Now let us learn how to check if a particular key is present in the dictionary. |
| 5:33 | For that we can use the method in, |
| 5:37 | So type within single quotes py in extensions. |
| 5:45 | Then type within single quotes odt in extensions. |
| 5:53 | It will return True if the key is found in the dictionary, and will return False if key is not present. |
| 6:00 | Note that we can check only for container-ship of keys in dictionaries and not values. |
| 6:07 | Now let us see how to retrieve the keys and values. |
| 6:10 | We can use the method keys() for getting a list of the keys in a particular dictionary and the method values() for getting a list of values. |
| 6:20 | Let us try them, type extensions dot keys closing brackets. |
| 6:31 | It returned the list of keys in the dictionary extensions. |
| 6:35 | And now the other one is extensions dot values and closing brackets. |
| 6:42 | It returned the list of values in the dictionary. |
| 6:45 | Pause the video here, try out the following exercise and resume the video. |
| 6:49 | Print the keys and values in the dictionary one by one. |
| 6:54 | Switch to terminal for solution. |
| 6:58 | Type for each in extensions dot keys closing brackets colon then,
print each comma within double quotes hyphen hyphen greater symbol, extensions and within closing brackets each. |
| 7:35 | This brings us to the end of this tutorial. |
| 7:39 | In this tutorial, we have learn't to, |
| 7:41 | 1. Create dictionaries namely -- - empty dictionaries - dictionaries with data. |
| 7:45 | 2. Access elements in the dictionaries using the keys. |
| 7:49 | 3. Add elements to a dictionary by assigning a key value. |
| 7:55 | 4. Delete elements from a dictionary by using the function del |
| 8:00 | 5. Retrieve the keys and values by using the methods .keys() and.values() respectively. |
| 8:06 | 6. Iterate over elements of a dictionary using a for loop. |
| 8:11 | Here are some self assessment questions for you to solve |
| 8:15 | 1. First one, Container-ship of values can be checked in a python dictionary - true or false. |
| 8:22 | 2. Second one is, Consider the python dictionary x is equal to within curly brackets 'a' colon ['a','b','c'], 'b' colon (1, 2, 3), 1 colon then again another curly braces 1 colon 'one' comma 2 colon 'two' comma 10 colon within curly brackets 10 colon 'ten', 11 colon 'eleven' and close the curly brackets. |
| 8:52 | What will the following code return? |
| 8:57 | (1, 2, 3) in x.values(). True. False |
| 9:05 | Then container-ship of values cannot be checked in dictionaries |
| 9:10 | The dictionary is invalid |
| 9:13 | So Lets look at the answers, |
| 9:16 | 1.The answer of first one, False. |
| 9:19 | Container-ship of only keys can be checked in a python dictionary. |
| 9:27 | 2. Second one is, True |
| 9:31 | Hope you have enjoyed this tutorial and found it useful. |
| 9:35 | Thank you! |
