CSV (Comma Separated Values) is a simple file format used to store tabular data, such as a spreadsheet or database. CSV file stores tabular data (numbers and text) in plain text. Each line of the file is a data record. Each record consists of one or more fields, separated by commas. The use of the comma as a field separator is the source of the name for this file format.
Python provides an in-built module called csv to work with CSV files. There are various classes provided by this module for writing to CSV:
- Using csv.writer class
- Using csv.DictWriter class
Using csv.writer class
csv.writer class is used to insert data to the CSV file. This class returns a writer object which is responsible for converting the user’s data into a delimited string. A csvfile object should be opened with newline='' otherwise newline characters inside the quoted fields will not be interpreted correctly.
Syntax: csv.writer(csvfile, dialect=’excel’, **fmtparams)
Parameters:
csvfile: A file object with write() method.
dialect (optional): Name of the dialect to be used.
fmtparams (optional): Formatting parameters that will overwrite those specified in the dialect.
csv.writer class provides two methods for writing to CSV. They are writerow() and writerows().
- writerow(): This method writes a single row at a time. Field row can be written using this method.
Syntax:
writerow(fields)
- writerows(): This method is used to write multiple rows at a time. This can be used to write rows list.
Syntax:
Writing CSV files in Python writerows(rows)
Example:
# Python program to demonstrate# writing to CSV import csv # field names fields = ['Name', 'Branch', 'Year', 'CGPA'] # data rows of csv file rows = [ ['Nikhil', 'COE', '2', '9.0'], ['Sanchit', 'COE', '2', '9.1'], ['Aditya', 'IT', '2', '9.3'], ['Sagar', 'SE', '1', '9.5'], ['Prateek', 'MCE', '3', '7.8'], ['Sahil', 'EP', '2', '9.1']] # name of csv file filename = "university_records.csv" # writing to csv file with open(filename, 'w') as csvfile: # creating a csv writer object csvwriter = csv.writer(csvfile) # writing the fields csvwriter.writerow(fields) # writing the data rows csvwriter.writerows(rows) |
Output:
Using csv.DictWriter class
This class returns a writer object which maps dictionaries onto output rows.
Syntax: csv.DictWriter(csvfile, fieldnames, restval=”, extrasaction=’raise’, dialect=’excel’, *args, **kwds)
Parameters:
csvfile: A file object with write() method.
fieldnames: A sequence of keys that identify the order in which values in the dictionary should be passed.
restval (optional): Specifies the value to be written if the dictionary is missing a key in fieldnames.
extrasaction (optional): If a key not found in fieldnames, the optional extrasaction parameter indicates what action to take. If it is set to raise a ValueError will be raised.
dialect (optional): Name of the dialect to be used.
csv.DictWriter provides two methods for writing to CSV. They are:
- writeheader():
writeheader()method simply writes the first row of your csv file using the pre-specified fieldnames.Syntax:
writeheader()
writerows():writerowsmethod simply writes all the rows but in each row, it writes only the values(not keys).Syntax:
writerows(mydict)
Example:
# importing the csv module import csv # my data rows as dictionary objects mydict =[{'branch': 'COE', 'cgpa': '9.0', 'name': 'Nikhil', 'year': '2'}, {'branch': 'COE', 'cgpa': '9.1', 'name': 'Sanchit', 'year': '2'}, {'branch': 'IT', 'cgpa': '9.3', 'name': 'Aditya', 'year': '2'}, {'branch': 'SE', 'cgpa': '9.5', 'name': 'Sagar', 'year': '1'}, {'branch': 'MCE', 'cgpa': '7.8', 'name': 'Prateek', 'year': '3'}, {'branch': 'EP', 'cgpa': '9.1', 'name': 'Sahil', 'year': '2'}] # field names fields = ['name', 'branch', 'year', 'cgpa'] # name of csv file filename = "university_records.csv" # writing to csv file with open(filename, 'w') as csvfile: # creating a csv dict writer object writer = csv.DictWriter(csvfile, fieldnames = fields) # writing headers (field names) writer.writeheader() # writing data rows writer.writerows(mydict) |
Output:
