Keeping Records: The American Pastime

Size: px

Start display at page:

Download "Keeping Records: The American Pastime"

Melanie Richards
5 years ago
Views:

1 Keeping Records: The American Pastime This exercise focuses on the modular design, implementation and testing of Python programs to process data files using lists and tuples. You and a partner will implement a Python program to manage information about baseball players. You will implement it in accordance with a modular design outlined in this exercise and in documentation in a starter program that we provide. Overview 1. The program will create and manipulate a dataset containing the following information for each player: player s name (string) team identifier (string) games played (integer) at bats (integer) runs scored (integer) hits (integer) home runs (integer) batting average (real) The first seven items will be read from a data file; the program will compute the last item using the following formula: batting average = (hits) / (at bats). A player with zero at bats is defined to have a batting average of zero. The program will represent the information for a player as a tuple, and the dataset as a list of tuples. 2. The program will recognize the following commands, where the first word in each is a keyword and the second word, if any, denotes information required to execute the command: QUIT HELP INPUT filename TEAM identifier HOMERS n The program will recognize commands entered with any mix of upper and lower case letters. The program will be operated interactively: it will repeatedly prompt the user for a command and then execute the command entered by the user from the keyboard. If the user enters an invalid command, the program will display an appropriate message and prompt the user to enter another command. 3. The QUIT command will halt execution.

2 4. The HELP command will display information to the user about the commands recognized by the program. 5. The INPUT command will contain a string indicating the name of an input file. The program will read the file to create a data set consisting of a list of tuples, where each tuple contains the information for one player. This will become the current dataset for future commands until the user indicates a new input file (by entering another INPUT command). An input file contains zero or more lines. A line that starts with a # is a comment line; your program will skip over comment lines. A correctly formatted non-comment line consists of the first seven items listed in 1 and separated by semicolons. For example: Cabrera, Miguel; DET; 148; 555; 103; 193; 44 If the user enters an invalid file name, the program will display an appropriate message and prompt the user to enter another command. If a non-comment line is improperly formatted, your program will display an informative error message, ignore the data in the line, and continue processing the rest of the file. 6. The TEAM command will contain a string representing a team identifier. The program will display all information about all players on that team, in alphabetical order. The player information will be displayed in tabular form. The fields will be identified using column headers and aligned beneath the headers. The program will print just the first 15 characters of any name longer than 15 characters. It will display real values with three digits of precision following the decimal point. (But save worrying about formatting for after you have finished implementing the program logic.) If the user enters an invalid team identifier, the program will display an appropriate message and prompt the user to enter another command; the program will not display an empty table. 7. The HOMERS command will be followed by a positive integer n. The program will report all information about the top n home-run hitters or, if n is larger than the number of players in the dataset, about all players. The report will be sorted in descending home-run order, starting with the player with the most home runs. Players with the same number of home runs will be displayed in alphabetical order. The information will be displayed in tabular form as in 6. If the user does not enter a positive integer for n, the program will display an error message and prompt the user to enter another command. If the player data set is empty, the program will display an error message and prompt the user to enter another command; it will not display an empty table. 8. If the user enters an invalid command, the program will display an appropriate message and prompt the user to enter another command; the program will not display an empty report.

3 9. You may not use any global variables in your program. All communication between the functions will be done using arguments, return values, and the constants defined at the beginning of the program. Get Ready: Download the following files into the same working directory: mlb.py a Python program containing some constant definitions and function stubs, which you will implement and use in your solution. mlb.2013.txt a sample input file containing information about players on the teams in Major League Baseball (MLB) in mlb.test.txt a smaller file containing information about some players and also containing some incorrectly formatted lines; this file will be useful for initial development and testing. The first 8 lines of that file are: # small data file to use in testing De Aza, Alejandro; CWS; 153; 607; 84; 160; 17 Hunter, Torii; DET; 144; 606; 90; 184; 17 Hamilton, Josh; LAA; 151; 576; 73; 144; 21 # the next line is missing the team ID Choo, Shin-Soo; 154; 569; 107; 162; 21 Upton, Justin; ATL; 149; 558; 94; 147; 27 Cabrera, Miguel; DET; 148; 555; 103; 193; 44 Before you do any coding, read the full documentation in mlb.py. Your program will implement the design described in the comments and docstrings. It will also use the symbolic constants defined at the start of the file in place of integer literals when indexing into playerinformation tuples. Implementation Strategy: We have started you out with a main code section that implements the QUIT and HELP commands. The starter program also recognizes an INPUT command, but just executes a print stub. Begin coding by deleting the last comment (# REPLACE) and extending the if-elif statement so that the program also recognizes if a TEAM command is entered, if a HOMERS command is entered, or if none of the five command keywords is entered. Use print stubs to print the command entered. Run the program and test that the logic to repeatedly prompt for commands is implemented correctly before proceeding further.

4 Next implement the read_file function. If the file cannot be opened for reading, the read_file function will return an empty list. 1 Otherwise, it will build the list of player information tuples to return as it processes each line of the file (in a for loop): Starting with an empty list (created before entering the for loop), in each iteration of the loop, it will calculate the tuple for a player from the information in the line and append the tuple to the list. To test the read_file function, run the program and enter quit. Then evaluate read_file( mlb.test.txt ) directly in the console. Check that it prints appropriate error messages for the two incorrectly formatted lines and that it returns a list containing a player information tuple for each correctly formatted line. Check several of the player information tuples the items should be of the specified types and in the same order as in the file. They should also contain a correct batting average (a float) as the final item. Also test calling read_file with a bad file name. It should print an error message and return an empty list. Next replace the print stub for the INPUT command with code implementing the command. This code will call read_file with the file name that the user entered in the command line. It will assign the return value to player_ds. To test your implementation of the INPUT command, run the program, enter INPUT mlb.test.txt at the first command prompt and enter quit at the second. Then evaluate player_ds in the console and check that it returns the expected list of player-information tuples. Run another test but with a bad file name this time. Continue in this fashion to implement the functions one-by-one and test them in the console. Then implement the commands that use the functions and test these commands. To simplify testing functions in the console, we recommend that you add an assignment after the while statement in the main code section such as ds = read_file( mlb.test.txt ) This will allow you to pass ds in for the roster parameter when you call a function in the console (e.g., to test get_team, you can evaluate get_team(ds, Det ) in the console). You will still need to quit the loop first. But it will save you having to retype the file name each time you want to test a function in the console. (When you are done testing your complete program, delete or comment out this assignment.) When you are satisfied that your code is correct, finally wrap the top-level code after all the function definitions in a main function definition and add a call to main at the end of your program. Test your program a final time. 1 Note that read_file does not repeatedly prompt for a file that it can open; instead, if the user enters a bad file name, it returns the empty list.

5 Suggestions for get_top_hitters: This is the most challenging function to implement because of the need to sort on two fields: the first (number of home runs) in descending order and the second (player names) in ascending order. Python provides both a sorted function and a sort method for lists. Both use lexicographic ordering when the items in a list are collections (e.g., tuples, lists, or strings). So if you were to sort the list passed in for roster, player information tuples would be sorted by player name, and then by team ID, and then by number of games played, etc. But you want to sort first by homeruns, not player names. One strategy for sorting the roster is outlined below. For concreteness, consider an example. Let s say the following list is passed in for roster. [('aname', 'cws', 153, 607, 84, 160, 17, ), ('fname', 'det', 144, 606, 90, 184, 17, ), ('bname', 'laa', 151, 576, 73, 144, 21, 0.25), ('ename', 'atl', 149, 558, 94, 147, 21, ), ('cname', 'det', 148, 555, 103, 193, 44, ), ('dname', 'col', 57, 165, 22, 40, 21, ), ('gname', 'cws', 1, 2, 0, 0, 0, 0.0)] From this list, you can create an intermediate list of two-tuples, where each tuple in the intermediate list contains the number of homeruns followed by the player information tuple: [(17, ('aname', 'cws', 153, 607, 84, 160, 17, )), (17, ('fname', 'det', 144, 606, 90, 184, 17, )), (21, ('bname', 'laa', 151, 576, 73, 144, 21, 0.25)), (21, ('ename', 'atl', 149, 558, 94, 147, 21, )), (44, ('cname', 'det', 148, 555, 103, 193, 44, )), (21, ('dname', 'col', 57, 165, 22, 40, 21, )), (0, ('gname', 'cws', 1, 2, 0, 0, 0, 0.0))] Calling the Python sorted function to sort this intermediate list produces: [(0, ('gname', 'cws', 1, 2, 0, 0, 0, 0.0)), (17, ('aname', 'cws', 153, 607, 84, 160, 17, )), (17, ('fname', 'det', 144, 606, 90, 184, 17, )), (21, ('bname', 'laa', 151, 576, 73, 144, 21, 0.25)), (21, ('dname', 'col', 57, 165, 22, 40, 21, )), (21, ('ename', 'atl', 149, 558, 94, 147, 21, )), (44, ('cname', 'det', 148, 555, 103, 193, 44, ))] But you want the home runs in descending order. So you can reverse this list to get another intermediate list: [(44, ('cname', 'det', 148, 555, 103, 193, 44, )), (21, ('ename', 'atl', 149, 558, 94, 147, 21, )), (21, ('dname', 'col', 57, 165, 22, 40, 21, )), (21, ('bname', 'laa', 151, 576, 73, 144, 21, 0.25)),

6 (17, ('fname', 'det', 144, 606, 90, 184, 17, )), (17, ('aname', 'cws', 153, 607, 84, 160, 17, )), (0, ('gname', 'cws', 1, 2, 0, 0, 0, 0.0))] You next want to collect the player information tuples from this intermediate list, but not exactly in the above order player information tuples with the same number of home runs need to be sorted in ascending order by the player name (they are currently in descending order). This can be done using nested while loops. Starting with an empty result list, each iteration of the outer loop can extend the result list with the list of properly sorted player information tuples for the next home run value. It can use a nested loop to build this latter list. Continuing with above example, the outer loop body will be executed four times. The first iteration will create a list of all player information tuples whose home run value is 44; it will then sort this list by player name, and extend the result list with the sorted list. The second iteration will create a list of all player information tuples whose home run value is 21, sort this list by player name, and extend the result list with the sorted list. And so on. Thus, after the first iteration of the outer loop, the result list will be: [('cname', 'det', 148, 555, 103, 193, 44, ))] After the second, it will be: [('cname', 'det', 148, 555, 103, 193, 44, )), ('bname', 'laa', 151, 576, 73, 144, 21, 0.25)), ('dname', 'col', 57, 165, 22, 40, 21, )), ('ename', 'atl', 149, 558, 94, 147, 21, ))] After the third, it will be: [('cname', 'det', 148, 555, 103, 193, 44, )), ('bname', 'laa', 151, 576, 73, 144, 21, 0.25)), ('dname', 'col', 57, 165, 22, 40, 21, )), ('ename', 'atl', 149, 558, 94, 147, 21, )), ('aname', 'cws', 153, 607, 84, 160, 17, )), ('fname', 'det', 144, 606, 90, 184, 17, ))] After the fourth, it will be: [('cname', 'det', 148, 555, 103, 193, 44, )), ('bname', 'laa', 151, 576, 73, 144, 21, 0.25)), ('dname', 'col', 57, 165, 22, 40, 21, )), ('ename', 'atl', 149, 558, 94, 147, 21, )), ('aname', 'cws', 153, 607, 84, 160, 17, )), ('fname', 'det', 144, 606, 90, 184, 17, )), ('gname', 'cws', 1, 2, 0, 0, 0, 0.0))] The function will then return this final result list.

CE151 ASSIGNMENT

CE151 ASSIGNMENT Set by: Mike Sanderson Credit: 20% of total module mark Deadline: 11.59.59, Monday 8 December Submission of this assignment will be via the online submission system; your programs may be tested during