Python-3.4.3/C3/Manipulating-strings/English-timed
From Script | Spoken-Tutorial
| Time | Narration |
| 00:01 | Welcome to the spoken tutorial on Manipulating Strings. |
| 00:06 | In this tutorial, we will learn to
Slice a string and get substrings out of them Reverse a string Replace characters in a string Convert a string to upper or lowercase and Join list elements to form a string |
| 00:27 | To record this tutorial, I am using
Ubuntu Linux 16.04 operating system Python 3.4.3 and IPython 5.1.0 |
| 00:43 | To practise this tutorial, you should know how to use
basic datatypes, operators, strings and lists If not, see the relevant Python tutorials on this website. |
| 00:59 | First let us see about string slicing. |
| 01:03 | String slicing allows us to obtain substrings. |
| 01:08 | The syntax for the string slicing is:
string_name inside square brackets start colon stop or string_name inside square brackets start colon stop colon step |
| 01:24 | Let us start ipython. Open the terminal. |
| 01:29 | Type ipython3 and press Enter. From here onwards, remember to press the Enter key after typing every command on the terminal. |
| 01:40 | Let us understand the string slicing with an example. Type, data is equal to inside double quotes python |
| 01:51 | Type, print inside brackets data inside square brackets 0 colon 3 |
| 01:59 | We get the sliced substring as pyt. |
| 02:03 | Note that, we are slicing the string from the index 0 to 3. |
| 02:09 | By doing so, the string elements from index 3 are not included. |
| 02:15 | Let us create a list, week underscore name which has names of the days of the week. |
| 02:21 | Type as shown. Type, s is equal to inside double quotes saturday |
| 02:31 | We need to check if the first three characters of the given string exists in the list week underscore name. |
| 02:39 | Strings can be sliced into substrings. |
| 02:43 | To get the first three characters of the string s, type, s inside square brackets 0 colon 3 |
| 02:52 | As you can see, the character at last index ie 3 is not included in the sliced output. |
| 03:00 | We will check if the substring of s is present in the list week underscore name. |
| 03:06 | Type s inside square brackets 0 colon 3 in week underscore name |
| 03:14 | We get the output as True which indicates that the substring is present in the list. |
| 03:20 | Pause the video. Try this exercise and then resume the video. |
| 03:26 | Obtain the substring excluding the first and last characters from the string s. |
| 03:32 | Switch back to terminal for the solution. |
| 03:36 | Type, s inside square brackets 1 colon -1 |
| 03:42 | As we already know, the last element of the string can be accessed using the index -1.
|
| 03:49 | Next let us learn to check if a given string is a palindrome or not. |
| 03:55 | A palindromic string is a string that is same as its reverse. |
| 04:01 | Type, s1 is equal to inside double quotes dad |
| 04:07 | Now, we need to compare this string with its reverse. |
| 04:11 | For reversing s1, we stride the string from the first to last character. |
| 04:17 | It is done by keeping the start and stop values as empty and step as -1. |
| 04:24 | That is s1 inside square brackets colon colon -1 |
| 04:30 | Now, we will check if the string s1 is a palindrome or not. |
| 04:35 | Type, s1 is double equal to s1 inside square brackets colon colon -1 |
| 04:44 | The output True indicates that it is a palindrome. |
| 04:49 | If the given string has capital D in dad instead of small d, the comparison would return False. |
| 04:57 | So, we have to convert the string to all lowercase or uppercase, before comparison. |
| 05:04 | Python provides the string methods lower and upper to achieve this. |
| 05:10 | Let's try it out. Type, s2 is equal to inside double quotes capital D ad |
| 05:19 | Type s2.upper open and close parentheses We get all the characters in uppercase. |
| 05:29 | Type s2 As you can see, s2 has not changed. |
| 05:36 | It is because, method upper returns a new string. It doesn't change the original string. |
| 05:43 | Let us compare the original and reversed string in lowercase.
Type as shown. As expected the output is True. |
| 05:56 | Pause the video. Try this exercise and then resume the video. |
| 06:02 | Check if each element in the following list is present in the list week underscore name. |
| 06:09 | Switch back to terminal for the solution. |
| 06:13 | Type as shown. It returns False for python as it is not there in the list week underscore name. |
| 06:24 | Next let us learn to use replace method. |
| 06:28 | Type, email is equal to inside double quotes info[at]fossee[dot]in |
| 06:36 | We often encounter email addresses which have @ symbol and periods replaced with text as shown. |
| 06:44 | Let us learn how to get back proper email addresses. |
| 06:49 | Now, we will first replace the [at] with the @ symbol, using the replace method. |
| 06:55 | Type as shown. You can see that the @ symbol is properly replaced now. |
| 07:05 | Pause the video. Try this exercise and then resume the video. |
| 07:11 | Replace the [dot] with '.' symbol in the given email. |
| 07:16 | Switch back to terminal for the solution. |
| 07:20 | Type as shown. |
| 07:24 | Now the variable email underscore proper has the email in the proper form. |
| 07:30 | Next, we will look at another interesting problem. |
| 07:34 | Let us say, we have a list of email addresses in the variable email underscore list as shown. |
| 07:41 | We will obtain one long string of email addresses, separated by commas or semicolons. |
| 07:48 | We will use the string method join for joining the list items into a single string. |
| 07:55 | Type as shown. Comma followed by a space will give the string with the same formatting. |
| 08:04 | Type, print inside parentheses email underscore str You can see that all the email addresses joined into a single string. |
| 08:16 | Pause the video. Try this exercise and then resume the video. |
| 08:22 | From the email underscore str, change the separator to semicolon instead of comma. |
| 08:29 | Switch back to terminal for the solution. |
| 08:33 | Type as shown. We see that the email addresses are joined by a semicolon followed by a space. |
| 08:43 | This brings us to the end of this tutorial. Let us summarize. |
| 08:49 | In this tutorial, we have learnt to,
Obtain substrings Reverse strings by using the index numbers |
| 08:58 | Use the following methods
upper() lower() replace() and join() |
| 09:05 | Here are some self assessment questions for you to solve
1. Given a string s = "this was a string”, how will you change it to "this wasn't a list"? 2. The string s is assigned as shown, change the string to "friends" |
| 09:25 | And the answers,
1. We will use the replace method to accomplish this. Here string and was in the statement will be replaced by list and wasn't respectively. |
| 09:39 | 2. In order to remove dots and to get substring we stride the string s. |
| 09:45 | To change the string to lowercase, we use the string method lower(). |
| 09:51 | Please post your timed queries in this forum. |
| 09:55 | Please post your general queries on Python in this forum. |
| 10:00 | FOSSEE team coordinates the TBC project. (16.45) |
| 10:04 | Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India. For more details, visit this website. |
| 10:14 | This is Priya from IIT Bombay signing off. Thanks for joining. |
