Python CSV Files Exercises With Answers

What does csv.DictReader return for each row?

1. A single string
2. An integer index
3. A list of every column
4. A dictionary keyed by the headercorrect

Answer: A dictionary keyed by the header

Why: The first row supplies field names, and each later row becomes a mapping.

What does writer.writerow do?

1. Writes one row and a line terminatorcorrect
2. Closes the file
3. Sorts all rows
4. Reads one row

Answer: Writes one row and a line terminator

Why: Each call writes one record to the output stream.

What does quoting=csv.QUOTE_ALL do?

1. Sorts the fields
2. Quotes only numbers
3. Quotes every fieldcorrect
4. Removes all quotes

Answer: Quotes every field

Why: QUOTE_ALL wraps every field in quotes, even when it does not contain a delimiter.

What does this code print?

import csv
from io import StringIO
rows = list(csv.reader(StringIO("a,b\n1,2\n")))
print(rows[1][1])

1. a
2. 2correct
3. 1
4. b

Answer: 2

Why: The second row is ['1', '2'], so index 1 is the string 2.

Complete the module import.

import ____
from io import StringIO

Answer: csv

Why: The csv module provides readers and writers.

Complete the reader that uses header names.

import csv
from io import StringIO
rows = list(csv.____(StringIO("name,score\nAda,92\n")))

Answer: DictReader

Why: DictReader maps each row to a dictionary.

Complete the method that writes one row.

import csv
from io import StringIO
buffer = StringIO()
writer = csv.writer(buffer)
writer.____(["a", "b"])

Answer: writerow

Why: writerow writes a single record.

Complete the quoting mode that quotes every field.

import csv
from io import StringIO
buffer = StringIO()
writer = csv.writer(buffer, quoting=csv.____)

Answer: QUOTE_ALL

Why: QUOTE_ALL is the all-fields quoting constant.

What does the program output?

import csv
from io import StringIO
print(next(csv.reader(StringIO("a,b\n1,2\n"))))

Answer: ['a', 'b']

Why: The first row is the list of two header strings.

What appears on the screen?

import csv
from io import StringIO
rows = list(csv.DictReader(StringIO("name,score\nAda,92\n")))
print(rows[0]["score"])

Answer: 92

Why: The score field for Ada is the string 92.

What is printed?

import csv
from io import StringIO
buffer = StringIO()
writer = csv.writer(buffer, quoting=csv.QUOTE_ALL)
writer.writerow(["a,b", "c"])
print(buffer.getvalue().strip())

Answer: "a,b","c"

Why: QUOTE_ALL wraps both fields, including the one with a comma.

What is the output?

import csv
from io import StringIO
buffer = StringIO()
writer = csv.writer(buffer)
writer.writerow(["a", "b"])
print(buffer.getvalue().strip())

Answer: a,b

Why: writerow writes the two fields separated by a comma.