Today we learn about lists!
Remember arrays from C++ ? 😀 If not, no worries – just think of any ‘To do’ list or ‘shopping list’! A list is a collection of variables – and there is no limit in the number of variables! You can have a list of two items to a thousand items and beyond!
Also, a list can have any type of variables in it – an integer list, a string list or even mix and match lists (lists containing different variable type). Because you do not have to explicitly define variables in Python like many other language – making lists is very easy – just throw in whatever variables you need to directly in your new list!
- Let’s create some lists. Type and run:
list1 = [3,2,1]
print(list1)
PPG = [ ‘Sugar’, ‘Spice’, ‘Everything Nice’]
print(PPG)
MR = [‘Mushfiqur Rahman’, ‘Bangladeshi’, 33, 36.31]
print (MR)
2. We can add more items to an already created list using ‘append()’
PPG.append(‘Chemical X’)
print(PPG)
list1.append(“Let’s go!”)
print(list1)
This fancy ‘thing1.thing2()’ system is a cool stuff in Python where thing 1 is called an ‘object’ or ‘class’ and thing2 is called a method. So the general format is object.method(). We use ‘methods’ to modify an ‘object’. We will learn more about these later.
3. We can also create a list the following way. This may look cumbersome – but this is for the times you do not know what are the items that are going to be in a list from the beginning. So you start with an empty list and you just add data as you go.
chaptersCompleted = []
chaptersCompleted.append(‘print’)
chaptersCompleted.append(‘variables’)
chaptersCompleted.append(‘strings’)
print(‘I completed the following topics in first week: %s’ %chaptersCompleted)
4. How do we extract an item from the list? We specify the index in square brackets! Please note that indexing starts form 0. So first item in a list is positioned at index 0, second item at index 1, third item at index 2 and so on.
secondNumber = list1[1]
print(secondNumber)
Print(‘The age of Mushfiqur Rahim is %d’ %(MR[2]))
5. Try accessing an index that is bigger that a list’s size.
print(PPG[10])
What happens?
This is one of the most common problems because we often have an n-size list and then use list[n] to extract the last item and get an out-of-range error. But the last item is actually at n-1!
6. To get the size of your list ( number of items in your list) you can use the function len().
print(len(PPG))
print(PPG)
Note that len() is a function (has the capacity to take in arguments) , not a method ( methods come after a ‘dot’ and takes no arguments). We will do functions later.
Exercise
Make a list of four or five or six shows you plan to watch and print the following .
I’ve prepared a list of {# of items in your list} shows to watch and am very excited to start with {first item in your list}!