Computer Science 101

1. Computer Science 101 Lists in Python

2. The need for lists • Often we need many different variables that play a similar role in the program • For example, suppose we have a temperature reading for each day of the year and need to manipulate these values several times within a program. • With simple variables, • We would need to use 365 variables. • We would not be able to loop over these variables.

3. Lists • A list is a numbered collection of variables. • The variables in a list share the same name and are distinguished from one another by their numbers or subscripts. • We can loop through the variables of a list by using a variable for the subscript. • The subscripts are always 0,1,…, size-1

4. temperature 75 82 68 58 67 79 70 65 63 61 temperature[4] Referencing List Elements • Suppose we have a list, temperature, for the temperature readings for the year. • The subscripts would be 0,1,…,364. • To refer to the reading for a given day, we use the name of the list with the subscript in brackets: temperature[4] for the fifth day.

5. Python Session

6. Python Session

7. Appending to a List • If we have a list, say scores, we can add a value, say num, to the list byscores.append(num)

8. “… and all the children are above average”

9. “… and all the children are above average”

10. Random numbers • For testing purposes or for simulations, it is convenient to let the computer generate random data for us. • In Python there is a library, random, that has a lot of tools for working with random numbers.

11. Randrange • random.randrange • random.randrange(num)gives a random number in range 0,…,(num-1) • random.randrange(num1,num2)gives random number in range num1,…,(num2-1)

12. Randrange

13. Random Lists • To build a random list of values, we can • Start with an empty list, [] • Then append random values to the list

14. Find Largest Example

15. Find Largest Example

16. Is there easier way to loop the list?