pythonw file stream operation and simple student management system

A, Python3 File (File) method

open () method

Python open () method is used to open a file and returns a file object in the file processing is required to use this function, if the file can not be opened, will throw OSError.

Note: Use the open () method must ensure that the closed file object that calls the close () method.

open () function accepts two parameters are used in the form of: a file name (file) and a mode (mode).

open(file, mode='r')

The complete syntax is:

open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)

Parameter Description:

• file: Required, file path (relative or absolute path).
• mode: Optional, the file open mode
• buffering: a buffer
• encoding: utf8 general use
• errors: error level
• newline: distinguish line break
• closefd: Incoming file parameter types
• opener:

Common file objects:

file object using open function to create, the following table lists the file objects commonly used functions:

No.	Method and Description
1	file.close () close the file. After closing the file can not read and write operations.
2	() file.flush internal refresh buffer files directly to the internal buffer of data written to the file immediately, rather than passively waiting for the output buffer written.
3	file.fileno () returns an integer file descriptor (file descriptor FD integer), it can be used in a method as read some of the underlying operating os module.
4	file.isatty () if the file is connected to a terminal device returns True, otherwise return False.
5	file.next () ** Python 3 in the File object does not support next () method. ** Returns the file the next line.
6	[File.read ( size]) Reads the specified number of bytes from the file, is not given, or if the reading of all negative.
7	[FILE.readline ( size]) to read the entire line, including "\ n" characters.
8	[file.readlines ( sizeint]) reads and returns a list of all the rows, if given sizeint> 0, the sum of the return line is approximately sizeint bytes, may be larger than the actual read value sizeint, because of the need to fill the buffer.
9	[file.seek (offset , The whence]) move the file to a specified location read pointer
10	file.tell () returns the current file position.
11	[file.truncate ( size]) the first line of the first character from the beginning of the file is truncated, file size characters, no size represents a cut from the current location; all the characters will be deleted after the cut, where the line breaks in the system represents a 2 Widnows character size.
12	file.write (str) the string to the file, it returns the written character length.
13	file.writelines (sequence) writes a list of strings to the file sequence, if necessary wrap will have their own line breaks added for each row.

Exercise to get started:

The two merged into a txt file

Code section:

file_temp1 = {}							#空字典用来存储从文件中读取的数据
file_temp2 = {}

def read_file():
    file1 = open('file1.txt', 'r')      #打开文件流
    lines1 = file1.readlines()          #返回列表
    for line in lines1:
        line = line.strip()
        content = line.split('，')
        file_temp1[content[0]] = content[1]
    file1.close()                       #关闭文件流
    with open('fiel2.txt', 'r') as file2:           #无需手动关闭文件流
        lines2 = file2.readlines()
        for line in lines2:
            line = line.strip()
            content = line.split('，')
            file_temp2[content[0]] = content[1]

def merge_file():
    lines = []
    header = "姓名\t  电话\t    邮箱\n"
    lines.append(header)            #插入到列表末尾、unshitf、浅拷贝
    for key in file_temp1:          #==for key in file_temp1.keys()
        line = ''
        if key in file_temp2:
            line = line + '\t'.join([key, file_temp1[key], file_temp2[key]])
            line += '\n'
        else:
            line = line + '\t'.join([key, file_temp1[key], ''])
            line += '\n'
        lines.append(line)
    for key in file_temp2:
        line = ''
        if key not in file_temp1:
            line += '\t'.join([key, '', file_temp2[key]])
            line += '\n'
        lines.append(line)
    with open('file3.txt', 'w') as newfile:         #创建并写入新文件
        newfile.writelines(lines)

read_file()
merge_file()

Second, real simple student management system, student data stored in the document, support CRUD

Students read data from a file -> into memory, perform CRUD -> Save the file back (new file)

#面向对象、封装
class StudentSys:

    #初始化
    def __int__(self):
        self.students = {}                           #字典存储学生信息
        file = open('file4.txt', 'r')
        lines = file.readlines()                     #一列表的形式返回数据
        if len(lines) > 0:                           #不为空则赋值、要知道文件里面的内容才能具体处理
            for key in lines:
                line = key.strip().split()
                self.students[line[0]] = line[1]
        file.close()

    #插入字典、判断是否存在
    def addStu(self):
        name = input("please input a student's name:\n")
        stuID = input("please input a unique student's ID:\n").strip()
        while True:
            if stuID in self.students:
                stuID = input("The student ID already exists, please enter again:\n").strip()
            else:
                break
        self.students[stuID] = name
        print("your operation is successful!")

    #输入ID、存在则删除
    def deleteStu(self):
        stuID = input("please inout a student's ID:\n").strip()
        while True:
            if stuID not in self.students:
                stuID = input("The student ID not exists, please enter again:\n").strip()
            else:
                break
        del(self.students[stuID])
        print("your operation is successful!")


    def updateStu(self):
        stuID = input("please inout a student's ID:\n").strip()
        while True:
            if stuID not in self.students:
                stuID = input("The student ID not exists, please enter again:\n").strip()
            else:
                break
        name = input("a student's name will be updated\n")
        self.students[stuID] = name
        print("your operation is successful!")

    def queryStu(self):
        stuID = input("please inout a student's ID:\n").str5ip()
        if stuID not in self.students:
            print("The student ID not exists!")
        else:
            print('find a student ID: ', stuID, 'name: ' + self.students[stuID])

    def showAll(self):
        print("total have", len(self.students), "students:")
        for stuID in self.students:
            print(stuID, '->', self.students[stuID])

    #写入本地文件、最终一次性写入
    def quitAndsave(self):
        file = open('file5.txt', 'w')
        lines = []          #空列表存储需要写入的信息
        for key in self.students:
            line = ''
            line += '\t'.join([ str(key), self.students[key] ])
            line += '\n'
            lines.append(line)
        file.writelines(lines)
        file.close()
        print("The program has been quit")

#实例化类
stuSys = StudentSys()
stuSys.__int__()

#主函数、try错误处理
while True:
    print('''****welcome to student management system**********
    1、add a new student
    2、delete a student
    3、update a student information
    4、query a student information
    5、show all students
    6、quit the program''')
    print("*" * 50)
    try:
        option = int(input("please input your options:\n"))
    except Exception:
        print("a error, please input a integer again!")
        option = int(input("please input your options:\n"))
    if option == 1:
        stuSys.addStu()
    elif option == 2:
        stuSys.deleteStu()
    elif option == 3:
        stuSys.updateStu()
    elif option == 4:
        stuSys.queryStu()
    elif option == 5:
        stuSys.showAll()
    elif option == 6:
        stuSys.quitAndsave()
        break
    else:
        print("a error, please input again!")