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Working with Lists in Python
Selecting List Elements I

Chris is interviewing candidates for a job. He will call each candidate in order, represented by a Python list:

calls = ['Ali', 'Bob', 'Cam', 'Doug', 'Ellie']

First, he’ll call 'Ali', then 'Bob', etc.

In Python, we call the order of an element in a list its index.

Python lists are zero-indexed. This means that the first element in a list has index 0, rather than 1.

Here are the index numbers for that list:

Element Index
'Ali' 0
'Bob' 1
'Cam' 2
'Doug' 3
'Ellie' 4

In this example, the element with index 2 is 'Cam'.

We can select a single element from a list by using square brackets ([]) and the index of the list item. For example, if we wanted to select the third element from the list, we’d use calls[2]:

>>> print(calls[2]) 'Cam'

Note that when accessing elements of an array, you must use an int as the index. If you use a float, you will get an error. This can be especially tricky when using division. For example print(calls[4/2]) will result in an error, because 4/2 gets evaluated to the float 2.0.

To solve this problem, you can force the result of your division to be an int by using the int() function. int() takes a number and cuts off the decimal point. For example, int(5.9) and int(5.0) will both become 5. Therefore, calls[int(4/2)] will result in the same value as calls[2], whereas calls[4/2] will result in an error.

Instructions

1.

Use square brackets ([ and ]) to select the element with index 4 from the list employees. Save it to the variable index4.

2.

Use print and len to display how many items are in employees.

3.

Paste the following code into script.py:

print(employees[8])

What happens? Why?

4.

Selecting an element that does not exist produces an IndexError.

In the line of code that you pasted, change 8 to a different number so that you don’t get an IndexError.

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