python數據文件讀寫

CSV格式讀寫

Comma-Separated Values 有時也稱為字元分隔值，因為分隔字元也可以不是逗號。以,分隔的文件叫csv，以\t分隔的叫tsv

需要註意的一點：分隔符

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)

如果文件是其他分隔符，如\n，則需要傳入分隔符類型。

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)

讀取

列表方式讀取

import csv

with open('data.csv','r',encoding='utf-8') as csvfile:
    reader = csv.reader(csvfile)
    for row in reader:
        # 讀取出的內容是列表格式的
        print(row,type(row),row[1])

字典方式讀取

import csv

with open('data.csv','r',encoding='utf-8') as csvfile:
    reader = csv.DictReader(csvfile)
    for row in reader:
        # 讀取的內容是字典格式的
        print(row['last_name'])

寫入

列表方式寫入

import csv

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

    # 寫入一行 
    writer.writerow(['1','2','3','4','5','5','6'])

    # 寫入多行
    writer.writerows([[0, 1, 3], [1, 2, 3], [2, 3, 4]])

字典方式寫入

import csv
with open('data.csv','a+',encoding='utf-8',newline='') as csvfile:
    filename = ['first_name','last_name']
    # 寫入列標題
    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格式讀寫

python內置json包提供了四個函數：dumps、dump、loads、load。不帶s的負責文件與字典的轉換。帶s的負責字元串和字典的轉換。

字典到字元串 string json.dumps(dict)

import json

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

字元串到字典 dict json.loads(string)

import json

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

字典到json文件 json.dump(dict, file)

import json

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

json文件到字典 dict json.load(file)

import json

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