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diff --git a/basic_python/list_tuples.rst b/basic_python/list_tuples.rst index f02bd13..58e263c 100644 --- a/basic_python/list_tuples.rst +++ b/basic_python/list_tuples.rst @@ -36,7 +36,6 @@ using negative indices.:: It is important to note here that the last element of the *List* has an index of -1. - ~~~~~~~~~~~~~ Concatenating ~~~~~~~~~~~~~ @@ -376,28 +375,6 @@ a sorted copy of the list. However the original list is left intact:: [5, 1, 3, 7, 4] -List Comprehensions -~~~~~~~~~~~~~~~~~~~ - -List Comprehension is a convenvience utility provided by Python. It is a -syntatic sugar to create *Lists*. Using *List Comprehensions* one can create -*Lists* from other type of sequential data structures or other *Lists* itself. -The syntax of *List Comprehensions* consists of a square brackets to indicate -the result is a *List* within which we include at least one **for** clause and -multiple **if** clauses. It will be more clear with an example:: - - >>> num = [1, 2, 3] - >>> sq = [x*x for x in num] - >>> sq - [1, 4, 9] - >>> all_num = [1, 2, 3, 4, 5, 6, 7, 8, 9] - >>> even = [x for x in all_num if x%2 == 0] - -The syntax used here is very clear from the way it is written. It can be -translated into english as, "for each element x in the list all_num, -if remainder of x divided by 2 is 0, add x to the list." - - Tuples ------ @@ -495,12 +472,55 @@ functions. They are also returned by some built-in functions and methods. And also there are some use cases like co-ordinate among other things. So *Tuples* are helpful. +Additional Syntax +----------------- + +The following additional syntax are introduced to make it easier to operate on +*Lists*. + +range() +~~~~~~~ + +The *range* function takes at least one argument and 2 additional optional +arguments. If two or more arguments are specified, the range function returns +a list of natural numbers starting from the first argument passed to it to the +second argument. The third argument, if specified is used as a step. Suppose +only one argument is specified, then *range* function returns a list of natural +numbers starting from 0 upto the argument specified:: + + >>> range(5, 10, 2) + [5, 7, 9] + >>> range(2, 15) + [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14] + >>> range(12) + [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11] + +for +~~~ + +The **for** keyword is used as a part of the looping construct. Unlike for loops +in other languages, Python's for is used to iterate through the elements of +sequences like *Lists*, *Tuples*, *Dictionaries*, etc. The syntax of the for loop +consists of **for**, followed by a variable to hold the individual or the current +element of the list during iteration and **in**, followed by the sequence and a +semicolon(':') The next line which is part of the **for** loop, i.e the statements +that are part of the loop should start with a new intend:: + + >>> names = ['Guido', 'Alex', 'Tim'] + >>> for name in names: + ... print "Name =", name + ... + Name = Guido + Name = Alex + Name = Tim + Conclusion ---------- This section on *Lists* and *Tuples* introduces almost all the necessary machinary required to work on *Lists* and *Tuples*. Topics like how to -iterate through these data structures will be introduced in the later -sections. +use these data structures in bigger more useful programs will be introduced +in the subsequent chapters. + |