CSV

CSV文件如何读写

写出这篇文章的原因主要是最近在看一本书《Python爬虫开发与实战-从入门到实战》里面提到了CSV这个模块，我立马进行了尝试，发现非常好用，比之前的xlwt好用多了。

关键是爬取到数据之后，整个存储数据的逻辑更容易理解（可能还是自己太菜吧😭）本文中介绍的通过pandas和CSV 模块对数据进行读写操作

写入文件

pandas写入

# 1-pandas写入

import pandas as pd

data = [{"name":"yangming","age":32,"height":180,"address":"shenzhen"},
        {"name":"xiaoming","age":24,"height":168,"address":"guangzhou"},
        {"name":"zhoujun","age":29,"height":184,"address":"shanghai"},
        {"name":"zhangshan","age":20,"height":170,"address":"changsha"}
       ]

df = pd.DataFrame(data)
df

	name	age	height	address
0	yangming	32	180	shenzhen
1	xiaoming	24	168	guangzhou
2	zhoujun	29	184	shanghai
3	zhangshan	20	170	changsha

# 将DataFrame存储为csv,index表示是否显示行名，default=True

df.to_csv("tocsvfile-pandas.csv",sep=",")
pd.read_csv("tocsvfile-pandas.csv")

	Unnamed: 0	name	age	height	address
0	0	yangming	32	180	shenzhen
1	1	xiaoming	24	168	guangzhou
2	2	zhoujun	29	184	shanghai
3	3	zhangshan	20	170	changsha

# ！！！如何理解index参数

df.to_csv("tocsvfile-pandas-1.csv",index=False,sep=",")
pd.read_csv("tocsvfile-pandas-1.csv")

	name	age	height	address
0	yangming	32	180	shenzhen
1	xiaoming	24	168	guangzhou
2	zhoujun	29	184	shanghai
3	zhangshan	20	170	changsha

csv写入

字典形式写入

### csv通过字典形式存储文件

import csv

data = [{"name":"yangming","age":32,"height":180,"address":"shenzhen"},
        {"name":"xiaoming","age":24,"height":168,"address":"guangzhou"},
        {"name":"zhoujun","age":29,"height":184,"address":"shanghai"},
        {"name":"zhangshan","age":20,"height":170,"address":"changsha"}
       ]

with open("information.csv","w",encoding="utf-8") as f:
    writer = csv.DictWriter(f,fieldnames=["name","age","height","address"])
    writer.writeheader()
    writer.writerows(data)  # 写入整个数据data-----用writerows
    writer.writerow({"name":"Peter","age":28,"height":176,"address":"shenzhen"})  # 单独写入一条数据----用writerow

import pandas as pd

data = pd.read_csv("information.csv")
data

	name	age	height	address
0	yangming	32	180	shenzhen
1	xiaoming	24	168	guangzhou
2	zhoujun	29	184	shanghai
3	zhangshan	20	170	changsha
4	Peter	28	176	shenzhen

列表形式写入

# with 语句写在开头，防止属性字段重复写入文件中
# 例子：简书APP之旅

with open("information-1.csv",'a',newline ='',encoding="utf-8") as f:
        writer = csv.DictWriter(f,fieldnames=["name","age","height","address"])
        writer.writeheader()

        for i in range(1,5):
            name_list = ["xiaoming","yanghong","peter","Tom"] * i
            age_list = [19,27,32,24] * i
            height_list = [176,180,172,183] * i
            address_list = ["shenzhen","guangzhou","shanghai","changsha"] * i

            infomation_list = []
            for j in range(len(name_list)):
                information = {
                    "name":name_list[j],
                    "age":age_list[j],
                    "height":height_list[j],
                    "address":address_list[j]
                }
                infomation_list.append(information)

        writer.writerows(infomation_list)

# 读取数据
import pandas as pd

data = pd.read_csv("information-1.csv")
data

	name	age	height	address
0	xiaoming	19	176	shenzhen
1	yanghong	27	180	guangzhou
2	peter	32	172	shanghai
3	Tom	24	183	changsha
4	xiaoming	19	176	shenzhen
5	yanghong	27	180	guangzhou
6	peter	32	172	shanghai
7	Tom	24	183	changsha
8	xiaoming	19	176	shenzhen
9	yanghong	27	180	guangzhou
10	peter	32	172	shanghai
11	Tom	24	183	changsha
12	xiaoming	19	176	shenzhen
13	yanghong	27	180	guangzhou
14	peter	32	172	shanghai
15	Tom	24	183	changsha

单行写入

import csv

# 1-设置文件头
fileHeader = ["name", "score"]

# 2-待写入3行数据
d1 = ["Wang", "100"]
d2 = ["Li", "80"]
d3 = ["xiaosi","92"]

# 3-写入数据
f = open("instance_1.csv", "w")
writer = csv.writer(f)   # 生成writer对象

# 写入的内容都是以列表的形式整体传入函数
# writer.writerows([fileHeader, d1, d2, d3])  # 这行等效于下面的三行代码

# 4-数据单个形式传入
writer.writerow(fileHeader)
writer.writerow(d1)
writer.writerow(d2)
writer.writerow(d3)

# 5-需要关闭文件！！！
f.close()

pd.read_csv("instance_1.csv")

	name	score
0	Wang	100
1	Li	80
2	xiaosi	92

上下文写入-with

import csv

# 文件头
fileHeader = ["name", "score"]

# 写入的两行数据
d1 = ["Wang", "100"]
d2 = ["Li", "80"]
d3 = ["xiaosi","92"]

# 写入数据

with open("instance_2.csv", "a") as f:
    writer = csv.writer(f)
    writer.writerows([fileHeader, d1, d2, d3])

pd.read_csv("instance_2.csv")

	name	score
0	Wang	100
1	Li	80
2	xiaosi	92

读文件

pandas读取文件

# 1-通过pandas读取文件

import pandas as pd

csvfile = pd.read_csv("information.csv")
csvfile

	name	age	height	address
0	yangming	32	180	shenzhen
1	xiaoming	24	168	guangzhou
2	zhoujun	29	184	shanghai
3	zhangshan	20	170	changsha
4	Peter	28	176	shenzhen

csv模块读取文件

# 2-通过csv模块读取文件

import csv

with open("information-1.csv") as f:
    csvfile = csv.reader(f)
    for line in csvfile:   # 不需要用readlines
        print(line)

['name', 'age', 'height', 'address']
['xiaoming', '19', '176', 'shenzhen']
['yanghong', '27', '180', 'guangzhou']
['peter', '32', '172', 'shanghai']
['Tom', '24', '183', 'changsha']
['xiaoming', '19', '176', 'shenzhen']
['yanghong', '27', '180', 'guangzhou']
['peter', '32', '172', 'shanghai']
['Tom', '24', '183', 'changsha']
['xiaoming', '19', '176', 'shenzhen']
['yanghong', '27', '180', 'guangzhou']
['peter', '32', '172', 'shanghai']
['Tom', '24', '183', 'changsha']
['xiaoming', '19', '176', 'shenzhen']
['yanghong', '27', '180', 'guangzhou']
['peter', '32', '172', 'shanghai']
['Tom', '24', '183', 'changsha']