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第五章 文件

5.1 文件的打开和关闭操作

打开一个当前目录下的文件，进行简单的操作后，关闭这个文件

paper = open('first', 'x')
paper.write("Welcome to Python File World!")
paper.close()
paper2 = open('first', 'r')
hello = paper2.readline()
print(hello)

知识点:

1. open()函数打开模式
2. 打开文件后记得关闭文件

5.2 文件的读写操作

文本文件的读写是按照字符串方式进行，二进制文件的读写是按照字节流进行

例 5.2 新建一个文件，并向文件内写入几行数据，写完后重新定位读写指针位置到文件的开头，输出全部文件的内容

paper = open('first', 'w+')
print(paper.read())

paper.write('Welcome to Python File World!\r\n')
paper.write('Python is very powerful!\r\n')

paper.write('Python is also interesting!\r\n')
print(paper.read())
paper.seek(0)
print(paper.read())
paper.close()

知识点:

1. 文件的读写方法

5.3 文本文件操作

例 5.3 读取一个记录了用户信息(账号和密码)的文本文件，用户信息包括账号名和密码两部分，文本中每行记录一条用户信息，账号和密码之间用空格隔开，查找文件是否存在一个账户名为 hello 的账号，如存在将其密码修改为 123456；若不存在，则在文件尾部追加一个 hello 账户信息，并设定密码为 123456.

print("文本内原始信息: ")
with open('User.txt', 'r', encoding='utf-8') as f:
    userlist = []
    for line in f.readlines():
        print(line.strip('\n'))
        user = line.strip('\n').split(' ')
        userlist.append(user)
flag = 0
for item in userlist:
    if item[0] == "hello":
        item[1] == "123456"
        flag = 1
if flag == 0:
    newUser = ["hello", "123456"]
    userlist.append(newUser)
print("修改后文本信息: ")
with open('User.txt', 'w', encoding='utf-8') as f_w:
    for item in userlist:
        f_w.write(item[0]+" "+item[1]+'\n')
        print(item[0]+" "+item[1])
if flag == 1:
    print("hello用户已存在,密码已修改!")
else:
    print("hello用户不存在,已创建此用户")

5.4 CSV 文件的读写

例 5.4 有一个存放学生信息的文件 student.csv，存有五名学生的学号、姓名、成绩信息，读取并显示文件内容，计算学生成绩的平均值，根据学生的成绩进行排序，并将排序后的结果写入新文件 student123.csv 中

student_xy = []
print("原文件的内容是:")
with open('student.csv', 'r', encoding='gb18030') as data:
    for line in data:
        print(line.strip())
        line = line.strip()
        student_xy.append(line.split('，'))
print("转换成列表后是: ")
print(student_xy)
print("课程的平均成绩是: ")
score = student_xy[1:]
sum = 0
for item in score:
    sum = sum+int(item[2])
average = sum/len(score)
print(average)
print("按照成绩排名是: ")
score = sorted(score, key=(lambda item: int(item[2])), reverse=True)
print(score)
with open('student123.csv', 'w', encoding='utf-8')as data:
    data.write('，'.join(student_xy[0])+'\n')
    for s in score:
        data.write('，'.join(s)+'\n')
print("排序后的新文件内容是: ")
with open('student123.csv', 'r', encoding='utf-8')as data:
    for line in data:
        print(line.strip())

知识点:

1. with 语句:使用 with 语句可以不用关闭
2. 文件目录方法

5.5 应用实例

问题描述:现有两个文件：一个是保存星座及其时间信息的文本文件，另一个是保存若干人姓名及其生日的“生日.csv”文件，现在要求将“生日.csv”文件中所有人的姓名、生日和星座写入文件“生日星座.csv”，同时将各个星座的人数统计出来，保存到文件“星座统计.txt”中。4 个文件的内容格式如图 5-1 所示。

import csv


def readtxt(filename):
    with open(filename, "r")as f:
        ls = []
        for line in f:
            s = line.strip("\n").split("，")
            ls.append(s)
        xing_all = []
        for row in ls:
            xing_one = []
            if len(row[2]) == 3:
                yue1 = row[2][0]
                ri1 = row[2][1:3]
            else:
                yue1 = row[2][0:2]
                ri1 = row[2][2:4]
            if len(row[3]) == 3:
                yue2 = row[3][0]
                ri2 = row[3][1:3]
            else:
                yue2 = row[3][0:2]
                ri2 = row[3][2:4]
            xing_one.append(row[1])
            xing_one.append(int(yue1))
            xing_one.append(int(ri1))
            xing_one.append(int(yue2))
            xing_one.append(int(ri2))
            xing_all.append(xing_one)
    return xing_all


def readcsv(filename, xing):
    with open(filename, "r") as f:
        f.readline()
        sr = f.readlines()
        people = []
        for item in sr:
            person = []
            per = item.strip("\n").split("\t")
            date = per[1].split("-")
            person.append(per[0])
            person.append(date[1]+"月"+date[2]+"日")
            for line in xing:
                if (int(date[1]) == line[1] and int(date[2]) >= line[2]) or (int(date[1]) == line[3] and int(date[2]) <= line[4]):
                    per.append(line[0])
                    break
            people.append(per)
    return people


def writecsv(filename, people):
    with open(filename, "w", newline="")as f:
        w = csv.writer(f)
        w.writerow(["姓名", "生日", "星座"])
        w.writerows(people)


def Stats(people):
    dict_num = {}
    for line in people:
        dict_num[line[2]] = dict_num.get(line[2], 0)+1
    return dict_num


def writetxt(filename):
    with open(filename, "w")as f:
        f.write("星座    人数"+"\n")
        f.write("-------------"+"\n")
        for key, value in dict_num.items():
            f.write(key+"  "+str(value)+"\n")


if __name__ == '__main__':
    list_xing = readtxt("星座.txt")
    list_people = readcsv("生日.csv", list_xing)
    writecsv("生日星座.csv", list_people)
    dict_num = Stats(list_people)
    writetxt("星座统计.txt")