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.
For example:↲
xxx,yyy↲
↲denotes enter Key to be pressed
(ii) The last record in the file mayor may not have an ending line break.
For 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.
For example:
field_name 1, field_name 2, field_name 3↲
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 mayor may not be enclosed in double quotes. If fields are not enclosed with double quotes, then double quotes may not appear inside the fields
For example:
"Red","Blue","Green"↲  
Black, White, Yellow 
(vi) Fields containing line breaks (CRLF), double quotes, and commas should be enclosed in double-quotes.
For example:
Red, ",", Blue CRLF 
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.
For example:
"Red, " "Blue", "Green",
White

We can write the csv file with quotes, by registering new dialects using csv.register_dialect() class of csv module.
Program:
import csv
info = [['SNO: 'Person: 'DOB'],
['1', '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\\ch13\\person.csv', 'w') as f:
writer = csv.writer(f, dialect='myDialect')
for row in info:
writer. writerow(row)
f.close()
Output
file: "Person.csv"
"SNO","Person", "DOB", "1", "Madhu", "18/12/2001"
"2, "Sowmya", "19/2/1998", "3", "Sangeetha",
"20/3/1999", "4", "Eshwar", "21/4/2000"
"5", "Anand", "22/5/2001".

1. CSV file - data with default delimiter comma(,)
2. CSV file - data with space at the beginning.
3. CSV file - data with quotes
4. CSV file - data with custom Delimiters
1. CSV file - data with default delimiter comma(,):
The following program read a file called "Sample1.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 opent('c.\\pyprg\\sample1.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']
2. CSV files - data with spaces at the beginning:
Consider the following file "Sample2.csv containing the following data when opened through notepad.

Program:
import csv
csv.register_dialect ['my Dialect', delimiters=', 'Skipinitialspace= True).
F = open ('c:\\Pyprgl\sample2.csv', 'r')
reader = CSV.reader (F, dialect = 'myDialect')
for row in reader:
print (row)
F.close()
Output:
['Topic 1', 'Topic 2', 'Topic 3']
['One', 'two', 'three']
['Example 1', 'Example 2', 'Example 3']
We can see in "Sample 2.csv" there are spaces after the delimiter due to which the output is also displayed with spaces.
These whitespaces can be removed, by registering new dialects using csv. register _dialect( ) class of csv module. A dialect describes the format of the csv file that is to be read. In dialects the Parameter "skipinitialspace" is used for removing whitespaces after the delimiter.
3. CSV File - Data with Quotes:
We can read the csv files with quotes, by registering new dialects using csv. register_dialect( ) class of csv module.
SNO,                   Quotes
1,  "The Secret to getting ahead is getting started".
2, "Excellence is a continuous process and not an accident."
3,  "Work hard dream big never give up and believe Yourself"
4, "Failure is the opportunity to begin again more intelligently".
5, "The successful warrior is the average man, with laser-like focus."
Program:
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)
Output:
['SNO, 'Quotes']
['1', 'The secret to getting ahead is getting started'.]
['2', 'Excellence is a continuous process and not an accident'.]
['3', 'Work hard dream big never give up and believe yourself'.]
['4', 'Failure is the opportunity to begin again more intelligently':]
['5', 'The successful warrior is the average man with laser- like focus':]
4. CSV files with custom Delimiters:
We can read csv file having custom the delimiter by registering a new dialect with the help of csv.register_dialect( ).
In the following file called "sample4.csv", each column is separated with |(Pipe Symbol)

Program:
import csv
Csv. register_dialect('myDialect', delimiter= '|')
with open (c:\\pyprg\sample 4.csv', 'r') as f:
reader = csv.reader (f, dialect = "my dialect")
for row is reader:
print (row)
f.close()
Output:
['Roll no', 'Name', 'City]
['12101', 'Arun', 'Chennai']
['12102', 'Meena', 'Kovai']
['12103', 'Ram', 'Nellai']