07.1 / Intro: What are lists?Lists are variables that can hold multiple values. A list can contain any type of variable (eg. integer, float, string, etc.) but typically a list will hold items of a single type (eg. all integers or strings).Variables Lists- has only one value -has multiple values- can be of any of the built in - can be composed of any type, types in Python but usually all of the same type- may have some useful methods, - has a bunch of useful methods eg. strings have methods, that you will want to usebut integers don’tLists use the square brackets - [ and ] for creation and accessing elements. When accessing elements you may use a single integer to obtain a single value. The index value starts at zero with the fist element. >>> albums = [] # this is an empty list>>> albums[]>>> type(albums)<type 'list'>>>> albums = [ "Some Cities", "The Koln Concert", "Stereolab","Brazil Classics 2"] # a list of 4 album names, each is a string>>> albums[0]'Some Cities'>>> albums[1]'The Koln Concert'>>> albums[2]'Stereolab'>>> albums[3]'Brazil Classics 2'A Basic ListLists are zero indexed. That is you start counting the first element of the list from 0. Slicing ListsYou can access a sub-section of a list using two indexes seperated by a colon - “:” Using two integers allows you to slice the list and create smaller list which just contains the elements from 0 up to (but not including) the index 3 element.For example:>>> albums = [ "Some Cities", "The Koln Concert", "Stereolab","Brazil Classics 2"]>>> albums[0:2]['Some Cities', 'The Koln Concert']The result is a list itself. The list will contain all of the elements from the first index up to but not including the element of the second index.>>> albums[1:3]['The Koln Concert', 'Stereolab']>>> albums[1:4]['The Koln Concert', 'Stereolab', 'Brazil Classics 2']Usually if you want a part of the list from some element to the end you simply leave off the second index.>>> albums[1:]['The Koln Concert', 'Stereolab', 'Brazil Classics 2']You can do the same type of thing with the first index.>>> albums[:2]['Some Cities', 'The Koln Concert']You can use negative numbers as index - the negatives numbers will move backwards from the end of the list - so index -1 will be the last element, -2 the second last, etc.>>> albums[-1]'Brazil Classics 2'>>> albums[-3]'The Koln Concert'>>> albums[-3:-1]['The Koln Concert', 'Stereolab']>>> albums[-1:-3][]Remember that [] is simple an empty list. Finding The Length of a ListIn [7]: albums = [ "Some Cities", "The Koln Concert", "Stereolab","Brazil Classics 2"]In [8]: len(albums)Out[8]: 4Note: this interpreter session is using iPython - which is part of your portable Python. I recommend you start using it if only for the tab completion.Exercises: 07.1Q1. Create a list with exactly the following, each as a string exactly as shown (imagine these are some marks form a test):758492628287Call this list marks. Not mark. Not markz. Just marks.Q2. Using the list from Q1 - print out the following (in this order):- the length of the list
- the first item
- the fifth item
- the second last item (using a negative index)
- the second last item (using the len function)
Q3. Using the list from Q1 - print out - the slice (sub-list) of the second to fourth items
- the last 3 items
Q4. Add the following items to your glossary: |
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