Syntax

List Vs Array

Python uses lists not arrays. However a lot of the GCSE and GCE exams will make reference to arrays. It is important that you understand the difference. The key differences are –

1. Arrays have a fixed size while lists are variable
2. Arrays do not have any built in functions they can use while lists do.
3. Lists can store many different data types while arrays can only store a single data type.

The sample code is taken from the video.

#  index   0  1 2 3  4  5  6  7  8  9 10 11 12 13 14
scores = [40,20,1,49,34,41,35,37,46,32,5,3, 1, 6, 54]
# square brackets allow access to the array
x = 0
scores[2] = 15
scores[12] = 17
runningTotal = 0
while x < len(scores):
	print scores[x], "index ", x
	scores[x] = scores[x] * 2
	print scores[x], "doubled at index ", x
	x = x + 1
print runningTotal / len(scores)

Key term

Array – Can store a set of values of the same datatype. The size of the array is fixed on creation.

List – A dynamic data structure which can grow and shrink over time. It can store any combination of data types.

Helpful links

Pwnict – introduction to python  arrays

Functions to use with lists

Further information on arrays

Test your skill

1. Take the code shown above and change it so it will display and store the square value of all of the numbers in the list.

#  index   0  1 2 3  4  5  6  7  8  9 10 11 12 13 14
scores = [40,20,1,49,34,41,35,37,46,32,5,3, 1, 6, 54]
# square brackets allow access to the array
x = 0
scores[2] = 15
scores[12] = 17
runningTotal = 0
while x < len(scores):
	print scores[x], "index ", x
	scores[x] = scores[x] * scores[x]
	print scores[x], "squared at index ", x
	x = x + 1
print runningTotal / len(scores)

2. Alter your code from task two so it caclualtes the square sum of all of the numbers in the array.

#  index   0  1 2 3  4  5  6  7  8  9 10 11 12 13 14
scores = [40,20,1,49,34,41,35,37,46,32,5,3, 1, 6, 54]
# square brackets allow access to the array
x = 0
scores[2] = 15
scores[12] = 17
runningTotal = 0
while x < len(scores):
	scores[x] = scores[x] * scores[x]
	runningTotal = runningTotal + scores[x]
	x = x + 1
print runningTotal

3. Attempt the peek a boo task