Python and CSV Files: Book Back Questions and Answers

Computer Science : Database concepts and MySql : Python and CSV Files

Evaluation

Part – I

Choose the best answer (1 Marks)

1.A CSV file is also known as a ….

(A) Flat File

(B) 3D File

(C) String File

(D) Random File

2.The expansion of CRLF is

(A) Control Return and Line Feed

(B) Carriage Return and Form Feed

(C) Control Router and Line Feed

(D) Carriage Return and Line Feed

3.Which of the following module is provided by Python to do several operations on the CSV files?

(A) py

(B) xls

(C) csv

(D) os

4.Which of the following mode is used when dealing with non-text files like image or exe files?

(A) Text mode

(B) Binary mode

(C) xls mode

(D) csv mode

5.The command used to skip a row in a CSV file is

(A) next()

(B) skip()

(C) omit()

(D) bounce()

6.Which of the following is a string used to terminate lines produced by writer()method of csv module?

(A) Line Terminator

(B) Enter key

(C) Form feed

(D) Data Terminator

7.What is the output of the following program? import csv d=csv.reader(open('c:\PYPRG\ch13\city.csv'))

next(d)

for row in d: print(row)

if the file called “city.csv” contain the following details

chennai,mylapore

mumbai,andheri

A) chennai,mylapore

(B) mumbai,andheri

(C) chennai

(D) chennai,mylapore 

mumba       mumbai,andheri

8.Which of the following creates an object which maps data to a dictionary?

(A) listreader()

(B) reader()

(C) tuplereader()

(D) DicReader ()

9.Making some changes in the data of the existing file or adding more data is called

(A)Editing

(B) Appending

(C) Modification

(D) Alteration

10.What will be written inside the file test.csv using the following program import csv

D = [['Exam'],['Quarterly'],['Halfyearly']]

csv.register_dialect('M',lineterminator = '\n')

with open('c:\pyprg\ch13\line2.csv', 'w') as f:

wr = csv.writer(f,dialect='M')

wr.writerows(D)

f.close()

(A) Exam Quarterly Halfyearly

(B) Exam Quarterly Halfyearly

(C)

        E

        Q

        H

(D)

          Exam,

          Quarterly,

          Halfyearly

Part – II

Answer the following questions (2 Marks)

1. What is CSV File?

Ans. A CSV file is a human readable text file where each line has a number of fields, separated by commas or some other delimiter.

2. Mention the two ways to read a CSV file using Python.

Ans. (i) CSV files have been used extensively in e-commerce applications because they are considered very easy to process.

(ii) There are two ways to read a CSV file.

(a) Use the csv modules reader function

(b) Use the DictReader class.

3. Mention the default modes of the File.

Ans. The default mode of csv file in reading and writing is text mode.

4. What is use of next() function?

Ans. next() function is used to skip the first row while sorting a CSV file or a selected column.

5. How will you sort more than one column from a csv file?Give an example statement.

Ans. To sort by more than one column you can use itemgetter with multiple indices, operator .itemgetter (1,2).

Syntax :

sortedlist = sorted(data, key=operator.itemget ter(Col_number),reverse=True)

Part – III

Answer the following questions       (3 Marks)

1. Write a note on open() function of python. What is the difference between the two methods?

Ans. Python has a built-in function open() to open a file. This function returns a file object, also called a handle, as it is used to read or modify the file accordingly.

2. Write a Python program to modify an existing file.

Ans. import csv

row = [‘3’, ‘Meena’,’Bangalore’]

with open(‘student.csv’, r’) as readFile:

reader = csv.reader(readFile)

lines = list(reader)  # list()- to store each row of data as a list

lines [3] = row

with open( student.csv’, ‘w’) as writeFile:

# returns the writer object which converts the user data with delimiter

writer = csv.writer(writeFile) #writerows()method writes multiple rows to a csv file

writer.writerows(lines)

readFile.close()

writeFile.close()

3. Write a Python program to read a CSV file with default delimiter comma (,).

Ans. import csv

csv.register_dialect('myDialect',delimiter =',',quoting=csv.QUOTE_ALL,

skipinitialspace=True)

f=open('c:\\pyprg\\quotes.csv',,r')

reader = csv.reader(f, dialect='myDialect')

for row in reader:

print(row)

4. What is the difference between the write mode and append mode.

Ans. The ‘w’ write mode creates a new file. If the file is already existing ‘w’ mode overwrites it. Where as ‘a’ append mode is used to add the data at the end of the file if the file already exists otherwise creates a new one.

5. What is the difference between reader() and DictReader() function?

Ans. The main difference between the csv.reader() and DictReader() is in simple terms csv.reader and csv.writer work with list/tuple, while csv. DictReader and csv.DictWriter work with dictionary. 

Part – IV

Answer the following questions       (5 Marks)

1. Differentiate Excel file and CSV file.

Ans.

Excel

• Excel is a binary file that holds information about all the worksheets in a file, including both content and formatting

• XLS files can only be read by applications that have been especially written to read their format, and can only be written in the same way.

• Excel is a spreadsheet that saves files into its own proprietary format viz. xls or xlsx

• Excel consumes more memory while importing data

CSV

• CSV format is a plain text format with a series of values separated by commas.

• CSV can be opened with any text editor in Windows like notepad, MS Excel, OpenOffice, etc.

• CSV is a format for saving tabular information into a delimited text file with extension. CSV

• Importing CSV files can be much faster, and it also consumes less memory

2. Tabulate the different mode with its meaning.

Ans.

Mode : Description

r'    : Open a file for reading, (default)

'w'  : Open a file for writing. Creates a new file if it does not exist or truncates the file if it exists.

‘x’ : Open a file for exclusive creation. If the file already exists, the operation fails.

‘a'  :  Open for appending at the end of the file without truncating it. Creates a new file if it does not exist.

't’ :  Opren in text mode, (default)

’b’ : Open in binary mode.

‘+’ : Open a file for updating (reading and writing)

3. Write the different methods to read a File in Python.

Ans. Read a CSV File Lsing Python :

There are two ways to read a CSV file.

(i) Use the csv modules reader function

(ii)  Use the DictReader class.

CSV Module’s Reader Function:

(i) You can read the contents of CSV file with the help of csv.reader() method. The reader function is designed to take each line of the file and make a list of all columns.

(ii) Then, you just choose the column you want the variable data for. Using this method one can read data from csv files of different formats like quotes (""), pipe (|) and comma (,).

The syntax for csv.readerf) is

 csv.reader(fileobject,delimiter,fmtparams) where

(iii) file object : passes the path and the mode of the file

(iv) delimiter:an optional parameter containing the standard dilects like , | etc can be omitted.

(v) fmtparams : optional parameter which help to override the default values of the dialects like skipinitialspace,quoting etc. can be omitted.

* CSV file - data with default delimiter comma (,)

* CSV file - data with Space at the beginning

* CSV file - data with quotes

* CSV file - data with custom Delimiters

CSV file with default delimiter comma (,): The following program read a file called “sample 1. csv” with default delimiter comma (,) and print row by row.

Program:

#importing csv

import csv

#opening the csv file which is in different location with read mode

with open('c:\\pyprg\\samplel.csv', 'r') as F:

#other way to open the file is f= ('c:\\pyprg\\sample1.csv', 'r')

reader = csv.reader(F)

# printing each line of the Data row by row print(row)

F.close()

Output:

['SNO', 'NAME', 'CITY']

['12101', 'RAM', 'CHENNAI']

['12102', 'LAVANYA', 'TIRUCHY']

['12103', 'LAKSHMAN', 'MADURAI']

Reading CSV File Into A Dictionary:

(i) To read a CSV file into a dictionary can be done by using DictReader class of csv module which works similar to the reader() class but creates an object which maps data to a dictionary.

(ii) The keys are given by the fieldnames as parameter. DictReader works by reading the first line of the CSV and using each comma separated value in this line as a dictionary key.

(iii) The columns in each subsequent row then behave like dictionary values and can be accessed with the appropriate key (i.e. fieldname).

(iv) If the first row of your CSV does not contain your column names, you can pass a fieldnames parameter into the DictReader s constructor to assign the dictionary keys manually.

(v) The main difference between the csv. reader() and DictReader() is in simple terms csv.reader and csv.writer work with list/tuple, while csv.DictReader and csv. DictWriter work with dictionary, csv. DictReader and csv. DictWriter take additional argument fieldnames that are used as dictionary keys.

(vi) For Example Reading “sample8.csv” file into a dictionary

Program:

import csv

filename = c:\\pyprg\\sample8.csv’

input_file =csv.DictReader(open(filename,’r’)) for row in input_file:

print(dict(row) ) #dict() to print data

Output:

{‘ItemName ‘: ‘Keyboard ‘, ‘Quantity’: ‘48’}

{‘ItemName ‘: ‘Monitor’ ‘Quantity’: ‘52’}

{‘ItemName ‘: ‘Mouse ‘, ‘Quantity’: ‘20’}

In the above program, DictReader() is used to read “sample8.csv” file and map into a dictionary. Then, the function dict() is used to print the data in dictionary format without order. Remove the dict() function from the above program and use print(row).Check you are getting the following output

OrderedDict([(‘ItemName ‘, ‘Keyboard ‘), (‘Quantity’, ‘48’)])

OrderedDict([(‘ItemName ‘, ‘Monitor’), (‘Quantity’, ‘52’)])

OrderedDict( [(‘ItemName ‘, ‘Mouse ‘), (‘Quantity’, ‘20’)])

4. Write a Python program to write a CSV File with custom quotes.

Ans. import csv

info = [[‘SNO’, ‘Person, ‘DOB’],

[T’,‘Madhu’,‘18/12/2001’],

[‘2’, ‘Sowmya’,’19/2/1998’],

[‘3’, ‘Sangeetha’,’20/3/1999’],

[‘4’, ‘Eshwar’, ‘21/4/2000’],

[‘5’, ‘Anand’, ‘22/5/2001’]]

csv.register_dialect(‘myDialect’,quoting=csv.QUOTE_ALL)

with open(‘c:\\pyprg\\chl3\\person.csv’, ‘w’) as f:

writer - csv.writer(f, dialect=’myDialect’)

for row in info:

writer, writero w( row)

f.close()

5. Write the rules to be followed to format the data in a CSV file.

Ans. Rules to be followed to format data in a CSV file:

(i) Each record (row of data) is to be located on a separate line, delimited by a line break by pressing enter key.

Example: ←^|

xxx,yyy ←^|

←^| denotes enter Key to be pressed

(ii) The last record in the file may or may not have an ending line break.

Example:

ppp, qqq←^|

 yyy, xxx

(iii) There may be an optional header line appearing as the first line of the file with the same format as normal record lines. The header will contain names corresponding to the fields in the file and should contain the same number of fields as the records in the rest of the file.

Example:

field_namel,field_name2,field_name3←^|

aaa,bbb,ccc ←^|

zzz,yyy,xxx CRLF(Carriage Return and Line Feed)

(iv) Within the header and each record, there may be one or more fields, separated by commas. Spaces are considered part of a field and should not be ignored. The last field in the record must not be followed by a comma. For example: Red , Blue

(v) Each field may or may not be enclosed in double quotes. If fields are not enclosed with double quotes, then double quotes may not appear inside the fields.

Example:

"Red","Blue","Green"←^|     #Field data with double quotes

Black,White,Yellow  #Field data without double quotes

(vi) Fields containing line breaks (CRLF), double quotes, and commas should be enclosed in double-quotes.

Example:

Red, “,”, Blue CRLF # comma itself is a field value.so it is enclosed with double quotes Red, Blue, Green

(vii) If double-quotes are used to enclose fields, then a double-quote appearing inside a field must be preceded with another double quote.

Example:

“Red, ” “Blue”, “Green”, # since double quotes is a field value it is enclosed with another double quotes ,, White