python data file reading and writing

CSV Format reading and writing

Comma separated values are sometimes referred to as character separated values because the separated characters can also be non commas. Separated files are called csv and separated files are called tsv

One thing to note: separator

import csv 

data=[]
with open(r'data.csv',) as csvfile:
    file_list = csv.reader(csvfile,'mydialect')
    for line in file_list:
        data.append(line)
print(data)

If the file is a different separator, such as \ n, you need to pass in the separator type.

import csv 

data=[]
with open(r'data.csv',) as csvfile:
    file_list = csv.reader(csvfile,delimiter='\t')
    for line in file_list:
        data.append(line)
print(data)

read

List mode read

import csv

with open('data.csv','r',encoding='utf-8') as csvfile:
    reader = csv.reader(csvfile)
    for row in reader:
        # The contents read out are in list format
        print(row,type(row),row[1])

Dictionary reading

import csv

with open('data.csv','r',encoding='utf-8') as csvfile:
    reader = csv.DictReader(csvfile)
    for row in reader:
        # The read content is in dictionary format
        print(row['last_name'])

Write in

List mode write

import csv

with open('data.csv','a+',encoding='utf-8',newline='') as csvfile:
    writer = csv.writer(csvfile)

    # Write to a row 
    writer.writerow(['1','2','3','4','5','5','6'])

    # Write multiple rows
    writer.writerows([[0, 1, 3], [1, 2, 3], [2, 3, 4]])

Dictionary mode write

import csv
with open('data.csv','a+',encoding='utf-8',newline='') as csvfile:
    filename = ['first_name','last_name']
    # Write as column title
    writer = csv.DictWriter(csvfile,fieldnames=filename)
    writer.writeheader()
    writer.writerow({'first_name':'wl','last_name':'wtx'})
    writer.writerow({'first_name': 'Lovely', 'last_name': 'Spam'})
    writer.writerow({'first_name': 'Wonderful', 'last_name': 'Spam'})

json Format reading and writing

python's built-in json package provides four functions: dumps, dump, loads, and load. Responsible for the conversion of files and dictionaries without s. With s responsible for string and dictionary conversion.

Dictionary to string json.dumps(dict)

import json

test_str = json.dumps({'name' : "cat"})

String to dictionary dict json.loads(string)

import json

test_dict = json.loads("{'name' : "cat"}")

Dictionary to JSON file json.dump(dict, file)

import json

with open("test.json","w") as f:
    json.dump({'name' : "cat"}, f)

JSON file to dictionary dict json.load(file)

import json

with open("test.json",'r') as f:
    test_dict = json.load(f)

Posted by ethridgt on Sun, 01 Dec 2019 12:56:10 -0800

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