读写CSV 文件

第三方库CSV中提供了2个类来写CSV文件

• csv.writer class

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)

• csv.DictWriter class

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(): writerows method simply writes all the rows but in each row, it writes only the values(not keys).
Syntax:
writerows()

同样，在读CSV文件时，也可以用 csv.DictReader() class和csv.reader()来读

import csv
def WriterCSV():
    fields = ['Name', 'Branch', 'Year', 'CGPA']
    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']]
    filename = "test1.csv"
    with open(filename, 'w', newline='') as csvfile:
        # 在以这种方法写CSV时，需要加newline=''，否则读CSV时，会有多个空列表，原因待确定
        # creating a csv writer object
        csvwriter = csv.writer(csvfile)
        # writing the fields
        csvwriter.writerow(fields)
        # writing the data rows
        csvwriter.writerows(rows)

def writerSCVDict():
    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'}]

    fields = ['name', 'branch', 'year', 'cgpa']
    filename = "test2.csv"
    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)


def ReadingCSV():
    import csv
    # opening the CSV file
    with open('test1.csv', mode='r')as file:
        # reading the CSV file
        csvFile = csv.reader(file)
        # displaying the contents of the CSV file
        for lines in csvFile:
            # if lines != '\n':
                print(lines)


def DictReaderCSV():
    import csv
    # opening the CSV file
    with open('test2.csv', mode='r') as file:
        # reading the CSV file
        csvFile = csv.DictReader(file)
        # displaying the contents of the CSV file
        for lines in csvFile:
            print(lines)

参考博客：
https://www.geeksforgeeks.org/reading-csv-files-in-python/?ref=lbp
https://www.geeksforgeeks.org/writing-csv-files-in-python/?ref=lbp