Data read / write: Python reads / writes CSV files

1. Read CSV file

csv.reader()

The effect of this method is equivalent to that of ',' Division csv Formatted data , And store the segmented data in the list , It also removes the space at the end of the data generated by the final segmentation of each row 、 A newline 、 Tabs and so on .

import csv
with open('data.csv',mode='r',encoding='utf-8-sig',newline='') as File:
# Use csv.reader() Read each line of data in the file into a list 
reader = csv.reader(File, delimiter=',', quotechar=',', quoting=csv.QUOTE_MINIMAL)
# Traverse the list to output data in rows 
for row in reader:
print(row)

Directly through Indexes To access the column elements of each row of data

for row in reader:
print(row[0])

csv.DictReader()

This method saves each line of data in the file in OrderedDict in , This data type is similar to a list nested with tuples , The first element in each tuple is the key , The second element is the value , The key in the tuple comes from CSV Header information in data .

import csv
results = []
with open('data.csv',mode='r',encoding='utf-8-sig',newline='') as File:
reader = csv.DictReader(File)
for row in reader:
print(row)

Read some information through key value

 for row in reader:
print(row['MakeSpan'],row['WaitTime'])

About DictReader() More content of has not been learned yet , Please refer to other articles if necessary ：CSV.DictReader() Method

2. write in CSV file

1. First, you need to import read / write csv Need a bag ：

import csv

1. Use open() Function to open a file ,open() Common parameters of functions ：

   file： File path 、 file name

   mode： Turn on mode ,r( read-only ),w( Just write ),a( Append mode )

   newline： Whether there is an empty line between each line , There are blank lines by default ,' '： There is no vacancy .

myFile = open('example2.csv', 'w', newline='')

1. csv.writer modular , Used to write data to CSV：

   csvfile： this can It's with write() Method .
   dialect=‘excel’： An optional parameter , Used to define specific CSV A set of parameters for .
   fmtparam： Optional parameters , Can be used to overwrite existing formatting parameters .

writer = csv.writer(myFile)

1. Use writerow() and writerows() Writes data to CSV In file ：

   writerow()： Save the data to csv In a line in the file , Each element occupies one cell

   writerows()： Save each list in the data to CSV In a line in the file , Each element in the list occupies one cell

myData1 = [[" this ", " yes ", "writerow", " Of ", " effect ", " fruit "],
[" this ", " yes ", "writerow", " Of ", " effect ", " fruit "],
[" this ", " yes ", "writerow", " Of ", " effect ", " fruit "]]
myData2 = [[" this ", " yes ", "writerows", " Of ", " effect ", " fruit "],
[" this ", " yes ", "writerows", " Of ", " effect ", " fruit "],
[" this ", " yes ", "writerows", " Of ", " effect ", " fruit "]]
myFile = open('example2.csv', 'w', newline='')
with myFile:
writer = csv.writer(myFile)
writer.writerow(myData1)
writer.writerows(myData2)

The effect of writing a file is as follows ：