CheckList 03

Overview

The third quiz will cover the following topics:

1. File I/O

2. Data Manipulation

The quiz will consist of definitions, short answers, code evaluation, translation, and programming sections.

Below are examples of the type of questions that may be asked on the quiz. It is meant to be representative, rather than exhaustive (ie. there may be questions that show up on the quiz that are not shown below).

Definitions

Briefly define the following terms.

1. File Handle

2. Text File

3. Binary File

4. CSV

5. JSON

6. IOError

Short Answer

1. Write some Python code that does each of the following:

   1. Reads all the contents of a file into a single string.

   2. Reads all the contents of a file into a list of strings.

   3. Prints out the contents of a file line-by-line.

   4. Lists the contents of a directory.

   5. Write all the items in a list of strings to a file.

   6. Write all the items in a dictionary to a file.

2. What are the four basic operations you can perform on a file (handle)?

3. Why should you close a file after opening it?

4. What are some reasons why an open would fail?

5. What are some advantages to using the csv Python module for parsing comma-separated-values, rather than simplying doing str.split?

Code Evaluation

Given the following turtles.csv file:

Name,Color,Weapon,Species
Leonardo,blue,katana,turtle
Donatello,purple,bo,turtle
Raphael,red,sai,turtle
Michelangelo,orange,nunchucks,turtle
Splinter,brown,staff,rat
Casey Jones,white,hockey stick,human
April O'Neil,yellow,microphone,human
Shredder,purple,armor,human

What is the result of the following Python code:

c = {}
for index, line in enumerate(open('turtles.csv')):
    if not index:
        continue

    d = line.strip().split(',')
    s = d[-1]

    c[s] = c.get(s, 0) + 1

for k, v in sorted(c.items()):
    print '{:8}: {}'.format(k, v)

Translation

Given the turtles.csv files and code above, modify the code to use the csv module instead of manually parsing the csv data.

Programming: CSV

Write a Python program that lets you look up a value in a CSV file by row number and column name.

def lookup_csv_value(csv_path, row_number, column_name):
    ''' Return the value in the file `csv_path` at the `row_number` for
    the column `column_name`.
    '''

# Examples using 'turtles.csv' file above
>>> lookup_csv_value('turtles.csv', 0, 'Name')
'Leonardo'

>>> lookup_csv_value('turtles.csv', 3, 'Weapon')
'staff'

Programming: JSON

Given the following URL:

http://xavier.h4x0r.space:9097/services.json

Using requests to fetch the JSON data and examine the data to count all the different opsys values from the services listed in the catalog:

def count_opsys(url):
    ''' Return a dictionary containing the counts of all the different
    `opsys` in the JSON data '''

>>> count_opsys('http://xavier.h4x0r.space:9097/services.json')
{u'Linux': 4}

Note: If the URL above does not work, try http://www3.nd.edu/~pbui/teaching/cdt.30010.fa16/static/json/services.json.