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.

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 read a csv file with comma (,)
#importing csv
import csv
#opening the csv file which is in different location with read mode
with open('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']

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:

(i) 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.
For Example:
>>>f = open ("sample.txt") #open file in current directory # f is file object
>>> f =  open ('c:\\Pyprg\ch13 sample5.csv') # specifying full path
(ii) The default is reading in text mode. In this mode, while reading from the file the data would be in the format of strings.
(iii) On the other hand, binary mode returns bytes and this is the mode to be used when dealing with non-text files like image or exe files.