\r and \n are the line terminator accepted by Python CSV module.

(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.

If an exception occurs when you are performing some operation with the file, the code exits without closing the file. The best way to do this is using the "with" statement. This ensures that the file is closed when the block inside with is exited.

To sort by more than one column you can use itemgetter with multiple indices:
operator.itemgetter 
Example:
sortedlist = sorted (data, key = operator. itemgetter(1))

The default is reading in text mode. In this mode, while reading from the file the data would be in the format of strings.

Import csv
csvData = [['Student, 'Age'], [Dhanush', '17'], ['Kalyani', '18'], ['Ram', '15']]
with open('c:\\pyprg\\ch13\\Pupil.csv', 'w') as CF:
writer = csv.writer(CF) # CF is the file object
writer.writerows(csvData) # csvData is the List name
CF.close( )

(i) Creating A New Normal CSV File
(ii) Modifying An Existing File
(iii) Writing on a CSV File with Quotes
(iv) Writing on a CSV File with Custom Delimiters
(v) Writing on a CSV File with Lineterminator
(vi) Writing on a CSV File with Quotechars
(vii) Writing CSV File Into A Dictionary
(viii) Getting Data At Runtime And Writing In a File

To create a CSV file using Microsoft Excel, launch Excel and then open the file you want to save in CSV format. For example. below is the data contained in our sample Excel worksheet:

Once the data is entered in the worksheet, select File ⟶ Save As option, and for the "Save as type option" select CSV (Comma delimited) or type the file name along with extension .csv.

Write mode:
Open a file for writing. Creates a new file if it does not exist or truncates the file if it exists.
Append mode:
Open for appending at the end of the file without truncating it. Creates a new file if it does not exist.

Program: To modify an existing file
import csv
row = ['3: 'Meena','Bangalore']
with open('Student.csv', 'r') as read file:
reader = csv.reader (read File)
lines = list (reader) 
lines [3] = row
with open ('Student.csv', 'w') as write file:
# 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()
Output:

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

The following program do the task mentioned above using operator.itemgetter(col_no)
Example:
# Program to sort the entire row by using a specified column.
# declaring multiple header files
import csv, operator
#One more way to read the file
data = csv.reader(open('c:\\PYPRG\ \sample8.csv'))
next(data) #(to omit the header)
#using operator module for sorting multiple columns
sortedlist = sorted (data, key=operator.
itemgetter(1) # 1 specifies we want to sort
# according to second column for row in sortedlist:
print(row)
Output:
['Mouse', '20']
['Keyboard', '48']
['Monitor', '52']

Import csv
#opening the csv file which is in different location with read mode
f=open("c:\\pyprg\\ch13ample5.csv",'r')
#reading the File with the help of csv.reader( )
readFile=csv.reader(f)
#printing the selected column
for col in readFile:
print col[0],col[3]
f.close ( )
Sample5.csv File in Excel

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