diff -r 88a01948450d -r d33698326409 manipulating-strings/script.rst --- a/manipulating-strings/script.rst Wed Nov 17 23:24:57 2010 +0530 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,255 +0,0 @@ -.. Objectives -.. ---------- - -.. By the end of this tutorial, you will be able to - -.. 1. Slice strings and get sub-strings out of them -.. #. Reverse strings -.. #. Replace characters in strings. -.. #. Convert strings to upper or lower case -.. #. joining a list of strings - -.. Prerequisites -.. ------------- - -.. 1. getting started with strings -.. #. getting started with lists -.. #. basic datatypes - -.. Author : Puneeth - Internal Reviewer : Amit - External Reviewer : - Language Reviewer : Bhanukiran - Checklist OK? : <08-11-2010, Anand, OK> [2010-10-05] - -Script ------- - -{{{ Show the slide containing title }}} - -Hello Friends. Welcome to this tutorial on manipulating strings. - -{{{ show the slide with outline }}} - -In this tutorial we shall learn to manipulate strings, specifically -slicing and reversing them, or replacing characters, converting from -upper to lower case and vice-versa and joining a list of strings. - -We have an ``ipython`` shell open, in which we are going to work, -through out this session. - -Let us consider a simple problem, and learn how to slice strings and -get sub-strings. - -Let's say the variable ``week`` has the list of the names of the days -of the week. - -:: - - week = ["sun", "mon", "tue", "wed", "thu", "fri", "sat"] - - -Now given a string ``s``, we should be able to check if the string is a -valid name of a day of the week or not. - -:: - - s = saturday - - -``s`` could be in any of the forms --- sat, saturday, Sat, Saturday, -SAT, SATURDAY. For now, shall now be solving the problem only for the forms, -sat and saturday. We shall solve it for the other forms, at the end of -the tutorial. - -{{{ show these forms in a slide }}} - -So, we need to check if the first three characters of the given string -exists in the variable ``week``. - -As, with any of the sequence data-types, strings can be sliced into -sub-strings. To get the first three characters of s, we say, - -:: - - s[0:3] - -Note that, we are slicing the string from the index 0 to index 3, 3 -not included. - -As we already know, the last element of the string can be accessed -using ``s[-1]``. - -Following is an exercise that you must do. - -%%1%% Obtain the sub-string excluding the first and last characters -from the string s. - -Please, pause the video here. Do the exercise(s) and then continue. - -:: - - s[1:-1] - -gives the substring of s, without the first and the last -characters of s. - -:: - - s = saturday - s[:3] - -Now, we just check if that substring is present in the variable -``week``. - -:: - - s[:3] in week - -Let us now consider the problem of finding out if a given string is -palindromic or not. First of all, a palindromic string is a string -that remains same even when it has been reversed. - -Let the string given be ``malayalam``. - -:: - - s = "malayalam" - -Now, we need to compare this string with it's reverse. - -Again, we will use a technique common to all sequence data-types, -[::-1] - -So, we obtain the reverse of s, by simply saying, - -:: - - s[::-1] - -Now, to check if the string is ``s`` is palindromic, we say -:: - - s == s[::-1] - -As, expected, we get ``True``. - -Now, if the string we are given is ``Malayalam`` instead of -``malayalam``, the above comparison would return a False. So, we will -have to convert the string to all lower case or all upper case, before -comparing. Python provides methods, ``s.lower`` and ``s.upper`` to -achieve this. - -Let's try it out. -:: - - s = "Malayalam" - - s.upper() - - s - -As you can see, s has not changed. It is because, ``upper`` returns a -new string. It doesn't change the original string. - -:: - - s.lower() - - s.lower() == s.lower()[::-1] - -Following is an exercise that you must do. - -%%2%% Check if ``s`` is a valid name of a day of the week. Change the -solution to this problem, to include forms like, SAT, SATURDAY, -Saturday and Sat. - -Please, pause the video here. Do the exercise and then continue. - -:: - - s in week - - s.lower()[:3] in week - - -So, as you can see, now we can check for presence of ``s`` in -``week``, in whichever format it is present -- capitalized, or all -caps, full name or short form. - -We just convert any input string to lower case and then check if it is -present in the list ``week``. - -Now, let us consider another problem. We often encounter e-mail id's -which have @ and periods replaced with text, something like -info[at]fossee[dot]in. We now wish to get back proper e-mail -addresses. - -Let's say the variable email has the email address. -:: - - email = "info[at]fossee[dot]in" - -Now, we first replace the ``[at]`` with the ``@``, using the replace -method of strings. -:: - - email = email.replace("[at]", "@") - print email - -Following is an exercise that you must do. - -%%3%% Replace the ``[dot]`` with ``.`` in ``email`` - -Please, pause the video here. Do the exercise and then continue. - -:: - - email = email.replace("[dot]", ".") - print email - -Now, let's look at another interesting problem where we have a list of -e-mail addresses and we wish to obtain one long string of e-mail -addresses separated by commas or semi-colons. - -:: - - email_list = ["info@fossee.in", "enquiries@fossee.in", "help@fossee.in"] - - -Now, if we wish to obtain one long string, separating each of the -email id by a comma, we use the join operator on ``,``. - -:: - - email_str = ", ".join(email_list) - print email_str - -Notice that the email ids are joined by a comma followed by a space. - -Following is an exercise that you must do. - -%%3%% From the email_str that we generated, change the separator to be -a semicolon instead of a comma. - -Please, pause the video here. Do the exercise and then continue. - -:: - - email_str = email_str.replace(",", ";") - -That brings us to the end of the tutorial. - -{{{ show summary slide }}} - -In this tutorial, we have learnt how to get substrings, reverse -strings and a few useful methods, namely upper, lower, replace and -join. - -{{{ Show the "sponsored by FOSSEE" slide }}} - -This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India - -Hope you have enjoyed and found it useful. -Thank you! -