1. Engineering Computing
Week 3

2. Lists Often we want to store multiple values.
Record how many students show up to class each day
Record the grades of students gets on their assignments
Lists contain 0 or more objects
Elements in the loop are separated by commas and contained within square brackets []
Ex.
# Number of whales seen per day
[6, 2, 4, 7, 3, 6, 64, 23, 5, 3, 7, 3, 8]

3. Lists >>>whales = [6, 2, 4, 7, 3, 6, 64, 23, 5, 3, 7, 3, 8]
How do we access individual elements? 1 2 3 4 5 6 7 8 9 10 11 12
whales 6 2 4 7 3 6 64 23 5 3 7 3 8

4. Accessing List Elements
>>>whales = [6, 2, 4, 7, 3, 6, 64, 23, 5, 3, 7, 3, 8] 1 2 3 4 5 6 7 8 9 10 11 12
whales 6 2 4 7 3 6 64 23 5 3 7 3 8
>>>whales[0]
>>>whales[12] 6 8
>>>whales[4]
>>>whales[103] 3
IndexError: list index out of range
>>>whales[8] 5

5. Accessing List Elements
>>>whales = [6, 2, 4, 7, 3, 6, 64, 23, 5, 3, 7, 3, 8] 1 2 3 4 5 6 7 8 9 10 11 12
whales 6 2 4 7 3 6 64 23 5 3 7 3 8
>>>whales[-1]
>>>whales[-4] 8
>>>whales[-2]
>>>whales[-13] 3 6
>>>whales[-3] 7

6. Slicing Lists
>>>whales = [6, 2, 4, 7, 3, 6, 64, 23, 5, 3, 7, 3, 8] 1 2 3 4 5 6 7 8 9 10 11 12
whales 6 2 4 7 3 6 64 23 5 3 7 3 8
>>>whales[1 : 4]
>>>whales[:]
[2,4,7]
[6, 2, 4, 7, 3, 6, 64, 23, 5, 3, 7, 3, 8]
>>>whales[ : 7]
>>>whales[1:-1]
[6,2,4,7,3,6,64]
[2, 4, 7, 3, 6, 64, 23, 5, 3, 7, 3]
>>>whales[2 : ]
[4, 7, 3, 6, 64, 23, 5, 3, 7, 3, 8]

7. Empty List emptyList= [] >>>emptyList[0]
The length of the empty list is 0
There are no legal indices in the emtpy list and there is no data to access
>>>emptyList[0]
IndexError: list index out of range
>>>emptyList[10]

8. Heterogeneity The elements in the list don’t just have to be numbers
>>> vowels = [`a’, `e’, `i’, `o’, `u’, `y’]
[`a’, `e’, `i’, `o’, `u’, `y’]
>>>vowels[0]
‘a’
>>>vowels[4]
‘u’
You can also mix and max elements
>>>stuff= [`a’, 1, ’hello’, -5.0]
[`a’, 1, ’hello’, -5.0]
>>>stuff[3]
-5.0
>>>stuff[0]
‘a’

9. Modifying List
We can use the same notation that we use to access lists to modify lists
>>> nobles = [‘helium’, ‘none’, ‘argon’, ’krypton’, ‘xenon’, ‘radon’]
>>>nobles[1]
‘none’
>>>nobles[1] = ‘neon’
>>>nobles
[‘helium’, ‘neon’, ‘argon’, ’krypton’, ‘xenon’, ‘radon’]

10. Built in List Functions
>>>numbers = [1, 5, 6, 3, 8, 2, 9, 20, 12, 20]
>>>len(numbers) #Length of the list 10
>>>max(numbers) #Maximum value in the list 20
>>> min(numbers) #Minimum number in the list 1
>>>sum(numbers) #Sum of the numbers in the list 86

11. Processing List Items 1 ‘a’ third 4
In Python, for loops are used to iterate over elements of a list.
They have a very familiar syntax.
for variable in list:
block
Example
list = [‘1’, 1, ‘a’, ‘third’, 4]
for i in list:
print i 1
‘a’
third 4

12. Common For Loops >>> list = [1,2,3,4,5]
>>>for i in list:
… print i*2 2 4 6 8 10
>>>for i in range(1,6,1) : … print I

13. Other Common For Loops
>>>for i in “abcdefg”: …. print i a b c d e f g >>>outer = [‘Li’, ‘Na’, ‘K’] >>>inner =[‘F’, ‘Cl’, ‘Br’]
#Nested For Loop for metal in outer: for gas in inner: print metal + gas LiF LiCl LiBr NaF NaCl NaBr KF KCl KBr

14. List Functions >>>list = [‘abc’, ’def’, ‘jkl’, ‘mno’, ‘pqr’]
>>>list.append(‘stu’); print list # append(v) appends v To End of List
[‘abc’, ’def’, ‘jkl’, ‘mno’, ‘pqr’, ‘stu’]
>>>list.insert(1,‘ghi’); print list #insert(i,v) inserts value v at index i
[‘abc’, ‘ghi’, ’def’, ‘jkl’, ‘mno’, ‘pqr’, ‘stu’]
>>>list.remove(‘abc’); print list #remove(v) removes first instance of v
[‘ghi’, ’def’, ‘jkl’, ‘mno’, ‘pqr’, ‘stu’]
>>>list.reverse(); print list
[‘stu’, ’pqr’, ’mno’, ’jkl’, ’def’, ’ghi’]

15. More List Functions
>>>list.sort(); print list #Sorts alphabetically or lo->hi
[’def’, ’ghi’, ‘jkl’, ‘mno’, ‘pqr’, ‘stu’]
>>>list.pop(); print list #Removes and returns last element
[’def’, ’ghi’, ‘jkl’, ‘mno’, ‘pqr’]