csv、json 文件读取

1、CSV 文件存储

1.1 写入

简单示例

import csv

with open('data.csv', 'a') as csvfile:
    writer = csv.writer(csvfile)       # 初始化写入对象，传入文件句柄
    writer.writerow(['id', 'name', 'age'])      # 调用 writerow() 方法传入每行的数据
    writer.writerow(['1', 'rose', '18'])
    writer.writerow(['2', 'john', '19'])

以文本方式打开，分隔符默认为逗号（,）：

id,name,age

1,rose,18

2,john,19

修改默认分隔符：

writer = csv.writer(csvfile, delimiter=' ')   	# 以空格为分隔符

同时写入多行：

# 此时参数为二维列表
writer.writerow([['1', 'rose', '18'], ['2', 'john', '19']])

避免出现空行，可以在写入时加 newline=''：

with open("test.csv", "a+", newline='') as csvfile:

---

如果数据源是字典

import csv

with open('data1.csv', 'a') as csvfile:
    fieldnames = ['id', 'name', 'age']      # 定义表头
    writer = csv.DictWriter(csvfile, fieldnames=fieldnames)         # 初始化一个字典，将文件句柄和表头传入
    writer.writeheader()        # 写入表头
    writer.writerow({'id': '1', 'name': 'rose', 'age': 18})     # 写入表格中具体内容

编码问题，需要指定 open() 函数编码格式：

open('data.csv', 'a', encoding='utf-8')

另外 pandas 库的 DataFrame 对象的 to_csv() 方法也可以将数据写入 csv 中。

1.2 读取

import csv

with open('data1.csv', 'r') as csvfile:
    reader = csv.reader(csvfile)
    for row in reader:
        print(row)

结果如下：

['id', 'name', 'age']
['1', 'rose', '18']

Tips：如果有中文需要指定文件编码

---

pandas 库的 read_csv() 方法

import pandas as pd

df = pd.read_csv('data.csv')
print(df)

运行结果如下：

   id  name  age
0   1  rose   18
1   2  john   19

1.3 避免重复插入表头

#newline的作用是防止每次插入都有空行    
with open("test.csv", "a+", newline='') as csvfile:		# 必须使用 a+，追加方式
        writer = csv.writer(csvfile)
        #以读的方式打开csv 用csv.reader方式判断是否存在标题。
        with open("test.csv", "r", newline="") as f:
            reader = csv.reader(f)
            if not [row for row in reader]:
                writer.writerow(["型号", "分类"])
                writer.writerows([[keyword, miaoshu]])
            else:
                writer.writerows([[keyword, miaoshu]])

示例

爬取一下该网站的所有评论：https://www.bestbuy.ca/en-ca/product/hp-hp-officejet-pro-6968-all-in-one-inkjet-printer-with-fax-6968/10441056/review

import requests
import time
import csv

headers = {
        "User-Agent": "Mozilla/5.0 (iPhone; CPU iPhone OS 11_0 like Mac OS X) AppleWebKit/604.1.38 (KHTML, like Gecko) "
                      "Version/11.0 Mobile/15A372 Safari/604.1",
        "Referer": "https://www.bestbuy.ca/en-ca/product/hp-hp-officejet-pro-6968-all-in-one-inkjet-printer-with-fax-"
                   "6968/10441056/review"
    }


def get_content(url):
    """爬取数据"""
    res = requests.get(url=url, headers=headers)
    # print(res.status_code)
    return res.json()


def parse_res(res):
    """解析数据"""
    csv_data = {}
    # print(res, type(res))
    data = res["reviews"]
    for i in data:
        csv_data["title"] = i["title"]
        csv_data["comment"] = i["comment"]
        csv_data["publish"] = i["reviewerName"]
        csv_data["publish_time"] = i["submissionTime"]
        print(csv_data)
        save_data(csv_data)


def save_data(csv_data):
    """存储数据"""
    with open('data.csv', 'a+', newline='') as csvfile:
        # 以读的方式打开 csv，判断表格是否有数据
        with open('data.csv', 'r', newline='') as f:
            reader = csv.reader(f)
            fieldnames = ['title', 'comment', 'publish', 'publish_time']
            writer = csv.DictWriter(csvfile, fieldnames=fieldnames)		# DictWriter： 字典
            if not [row for row in reader]:
                writer.writeheader()
                writer.writerow(csv_data)
            else:
                writer.writerow(csv_data)

if __name__ == '__main__':
    for i in range(1, 11):
        url = 'https://www.bestbuy.ca/api/v2/json/reviews/10441056?source=all&lang=en-CA&pageSize=10&page=%s' 
              '&sortBy=date&sortDir=desc' % i
        res = get_content(url)
        time.sleep(2)
        parse_res(res)

参考文章：https://blog.csdn.net/qq_41817302/article/details/88680886

2. JSON 文件存储

2.1 读取 JSON

import json

s = '''
    [{
        "name": "rose",
        "gender": "female",
        "age": "18"
    }]
'''

data = json.loads(s)
print(data)
print(type(data))

运行结果如下：

[{'name': 'rose', 'gender': 'female', 'age': '18'}]
<class 'list'>			# 因为最外层是列表

读取 JSON 文件

with open('data.json', 'r') as f:
    s = f.read()
    data = json.loads(s)
    print(data)

2.2 输出 JSON

import json

data = [{
        "name": "rose",
        "gender": "female",
        "age": "18"
    }]


with open('data.json', 'a') as f:
    f.write(json.dumps(data))

缩进 2 个字符，这样结构更清晰：

with open('data.json', 'a') as f:
    f.write(json.dumps(data, indent=2))

运行结果如下：

[
  {
    "name": "rose",
    "gender": "female",
    "age": "18"
  }
]

如果输出的包含中文，须臾指定参数 ensure_ascii=False，否则默认转换为 Unicode 字符：

with open('data.json', 'a') as f:
    f.write(json.dumps(data, indent=2, ensure_ascii=False))