Using Lists

Example 9.1. Using lists
#!/usr/bin/python
# Filename: using_list.py
# This is my shopping list
shoplist = ['apple', 'mango', 'carrot', 'banana']

print 'I have', len(shoplist), 'items to purchase.'
print 'These items are:', # Notice the comma at end of the line
for item in shoplist:
print item,
print '\nI also have to buy rice.'
shoplist.append('rice')
print 'My shopping list is now', shoplist
print 'I will sort my list now'
shoplist.sort()
print 'Sorted shopping list is', shoplist
print 'The first item I will buy is', shoplist[0]
olditem = shoplist[0]
del shoplist[0]
print 'I bought the', olditem
print 'My shopping list is now', shoplist
Output
$ python using_list.py
I have 4 items to purchase.
These items are: apple mango carrot banana
I also have to buy rice.
My shopping list is now ['apple', 'mango', 'carrot', 'banana', 'rice']
I will sort my list now
Sorted shopping list is ['apple', 'banana', 'carrot', 'mango', 'rice']
The first item I will buy is apple
I bought the apple
My shopping list is now ['banana', 'carrot', 'mango', 'rice']
How It Works
The variable shoplist is a shopping list for someone who is going to the market. In shoplist, we
only store strings of the names of the items to buy but remember you can add any kind of object to a list
including numbers and even other lists.
We have also used the for..in loop to iterate through the items of the list. By now, you must have
realised that a list is also a sequence. The speciality of sequences will be discussed in a later section
Notice that we use a comma at the end of the print statement to suppress the automatic printing of a
line break after every print statement. This is a bit of an ugly way of doing it, but it is simple and gets
the job done.
Next, we add an item to the list using the append method of the list object, as already discussed before.
Then, we check that the item has been indeed added to the list by printing the contents of the list by
simply passing the list to the print statement which prints it in a neat manner for us.
Then, we sort the list by using the sort method of the list. Understand that this method affects the list

itself and does not return a modified list - this is different from the way strings work. This is what we
mean by saying that lists are mutable and that strings are immutable.
Next, when we finish buying an item in the market, we want to remove it from the list. We achieve this
by using the del statement. Here, we mention which item of the list we want to remove and the del
statement removes it fromt he list for us. We specify that we want to remove the first item from the list
and hence we use del shoplist[0] (remember that Python starts counting from 0).
If you want to know all the methods defined by the list object, see help(list) for complete details.