>A Byte of Python

List

A list is a data structure that holds an ordered collection of items i.e. you can store a sequence of items in a list. This is easy to imagine if you can think of a shopping list where you have a list of items you want to buy, except that you probably have each item on a separate line in your shopping list whereas in Python you put commas in between them.

The list of items should be enclosed in square brackets so that Python understands that you are specifying a list. You can add, remove or search for items in a list.

The variable shoplist is a shopping list for someone who is going to the market. Here, I am storing just strings in the list but remember that you can add anything to the list i.e. you can add any object to the list - even numbers or other lists.

We have also used the for..in loop to go through the items of the list. By now, you should have realised that a list is also an example of a sequence. The speciality of sequences will be discussed in detail later.

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 gets the job done.

Next, we add an item to the list using the append method of the list object, as discussed before. Then, we check that the item has been indeed added to the list by printing the contents of the list. Note that the print statement automatically prints the list in a neat manner for us.

Then, we sort the list by using the sort method of the list object. Remember that this method affects the list itself and does not return a changed list - this is different from strings. 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 using the del statement. Here, we mention which item of the list we want to remove and the del statement removes it from the list for us. Then, we just print the list to check that it has been indeed removed from the list.

We can access members of the list by using their position as shown above. Remember that Python starts counting from 0. Therefore, if you want to access the first item in a list then you can use mylist[0] to get the first item in the list.

If you want to know all the methods defined by the list object, see help(list) for complete details.