Class 10 – Wednesday, September 15
Listing
Lest we go forward — Without knowing about lists — We would be wanting
Look both ways
Agenda
- Make loops right
- Provide you more background on list basics
Important survey
- Please take this voluntary survey
For the fun of it
- Reveal one of your super power(s).
Alert
- Anyone who asks me today about built-in function
sum()
earns negative ducks.
To do list
- Review class artifacts.
- Review epistles
- Complete homework
- Tell me about lists
- Tell me more about lists
Downloads
- Program wowzers.py
- Loop through and analyze lists
- Program on_average.py
- Determine average word length
- Program all_int.py
- Converts a list of integer inputs in to a list of integers.
- Program summing.py
- Accumulate a sum of values
Program wowzers.py
-
Task
- Loop through a string, list of words, and a list of numbers
- Analyze a list using built-in functions
-
Possible program run
Enter your favorite color: teal
Enter some names: willy evander aurelius ann
color = teal
names = ['willy', 'evander', 'aurelius', 'ann' ]
numbers = [12, 7, -11, -12, 59]
T
E
A
L
Willy
Evander
Aurelius
Ann
-12
-7
11
12
-59
t e a l
['willy', 'evander', 'aurelius', 'ann' ]
[5, 7, 8, 3]
length of longest name: 8
first alphabetically = ann
Accumulation
- Many times problem solving requires we analyze some sequence (e.g, string or list) to determine a property or build a new sequence. The determination can require each element in the sequence, contribute (accumulate) to the answer. For example, from text determine average word length or from numbers determine their absolute values or from a string determine its reverse.
- If the answer requires the items in list contribute to a total, then an accumulation is needed of the individual terms — the accumulator is updated by repeatedly adding to it. For this to work out, the accumulator needs to be initialized before the list is processed. For totaling, the accumulator is initialized to zero.
- Data processing can require a list be built out of some input data. Here, the accumulator needs to be initialized to the empty list [].
- Sometimes data processing can require the product of some numeric data. Here, the accumulator needs to be initialized to 1.
- Data processing can require a string be built character by character. For this to work out, a string accumulator needs to be intialized to the empty string ''.
Program on_average.py
-
Problem
- Examines a list of user-supplied words and reports determine average word length.
-
Realizations
- Because the number of words is not know when the program is being written, a loop is needed to process the words.
- To compute the average word length, need to know the number of words and the sum of the word lengths.
- The loop needs to two things for each word: compute its length and add its length to a running total.
- The running total needs to be initialized before the loop.
-
Algorithm
- Prompt and get text (i.e., a bunch of words).
- Split input into a word list.
- Echo word list to user.
- Compute the length of the list.
- Initialize running total of word lengths to 0.
- Process each word in the word list:
- Compute length of the current word of interest.
- Add that length to running total of the word lengths.
- Compute average from the word lengths total and the number of words.
- Print average.
-
Two program runs
Enter text: over the hill and through the dale
words = ['over', 'the', 'hill', 'and', 'through', 'the', 'dale']
Average word length: 4.0
Enter text: row row row your boat
words = ['row', 'row', 'row', 'your', 'boat']
Average word length: 3.4
List accumulation — program all_int.py
-
Task
- Produce a list of integers from user-supplied data.
-
Realizations
- Function
int()
can only be applied to one string at a time.
- List of integers will need to be accumulated by processing the numeric strings one at a time.
- For each numeric string it will need to be converted to an integer and added to the list of integers being built
- The list of integers needs to be initalized to an empty list.
-
Algorithm
- Prompt and get text (i.e., a list of integers).
- Split input into a list of numeric strings.
- Echo list of numeric strings.
- Initialize running list of integers to empty list
- Process each string in the numeric strings list:
- Get integer representation of the string.
- Add integer to the list accumulation
- Print accumulation.
-
Some program runs
Enter integers: 3 1 4 1 5 9
nbr_strings: ['3', '1', '4', '1', '5', '9']
numbers: [3]
numbers: [3, 1]
numbers: [3, 1, 4]
numbers: [3, 1, 4, 1]
numbers: [3, 1, 4, 1, 5]
numbers: [3, 1, 4, 1, 5, 9]
Enter integers: 58 2 37 16 99 1 9 23
nbr_strings: ['58', '2', '37', '16', '99', '1', '9', '23']
numbers: [58]
numbers: [58, 2]
numbers: [58, 2, 37]
numbers: [58, 2, 37, 16]
numbers: [58, 2, 37, 16, 99]
numbers: [58, 2, 37, 16, 99, 1]
numbers: [58, 2, 37, 16, 99, 1, 9]
numbers: [58, 2, 37, 16, 99, 1, 9, 23]
-
Code
# get input
reply = input( 'Enter integers: ' )
print()
# split reply into list of numeric strings
nbr_strings = reply.split()
# see what we got
print( 'nbr_strings:', nbr_strings )
print()
# convert numeric text into list of numbers
# begin with setting up the accumulator
numbers = [] # initialize holder to prepare for adding elements
# process the strings of nbr_strings one-by-one
for ns in nbr_strings :
# process the current numeric string
nbr = int( ns ) # get numeric equivalent of ns
numbers.append( nbr ) # add equivalent to list of numbers
print( 'numbers:', numbers ) # print the updated list of numbers
Host of Flying Monkey Manor
Willy Mays
Marcus Aurelius
Evander of Pallantium