python进阶(7)--文件与异常

一、文件读取
二、文件写入
三、异常
四、存储数据

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一、文件读取

1、with语句

#采用idea的sources root的相对路径
with open('..//data//pi_digits.txt') as file_object:
    contents = file_object.read()
#打印同时剔除空行
print(contents.rstrip())

查看结果：

3.1415926535
  8979323846
  2643383279

2、绝对路径

file_path='D:/Users/Mr.White/PycharmProjects/pythonProject/data/pi_digits.txt'
with open(file_path) as file_object:
    contents = file_object.read()
print(contents.rstrip())

查看结果：

3.1415926535
  8979323846
  2643383279

3、for循环逐行读取

with open('../data/pi_digits.txt') as file_object:
    for line in file_object:
        print(line.rstrip())

查看结果：

3.1415926535
  8979323846
  2643383279

4、readline()方法，将文件的内容存储在列表内

with open('../data/pi_digits.txt') as file_object:
    lines=file_object.readlines()
for line in lines:
    print(line.rstrip())

查看结果：

3.1415926535
  8979323846
  2643383279

优化代码，拼接字符串读取

with open('../data/pi_digits.txt') as file_object:
    lines=file_object.readlines()
pi_string=''
for line in lines:
    pi_string+=line.strip()
print(pi_string)
print(len(pi_string))

查看结果：

3.141592653589793238462643383279
32

 

二、文件写入

1、with，覆盖模式

file_name='../data/programming.txt'
with open(file_name,'w') as file_object:
    file_object.write("I love programming.")

查看文件(../data/programming.txt)：

I love programming.

2、写入多行

file_name='../data/programming.txt'
with open(file_name,'w') as file_object:
    file_object.write("I love programming.
")
    file_object.write("i love creating new games.
")

查看文件(../data/programming.txt)：

I love programming.
i love creating new games.

3、with，附加模式

with open(file_name,'a') as file_object:
    file_object.write("I also love fing...
")
    file_object.write("i love creating apps that...
")

查看文件(../data/programming.txt)：

I love programming.
i love creating new games.
I also love fing...
i love creating apps that...

 

三、异常

1、解决异常(ZeroDivisionError)：try except

try:
    print(5/0)
except ZeroDivisionError:
    print("You can't divide by zero!")

查看结果：

You can't divide by zero!

2、解决异常(FileNotFoundError):try except

filename="testfile.txt"
try:
    with open(filename,encoding='utf-8') as f:
        contents=f.read()
except FileNotFoundError:
    print(f"sorry,the file {filename} does not exits.")

查看结果：

sorry,the file testfile.txt does not exits.

3、异常时静默处理：pass

try:
    print(5/0)
except ZeroDivisionError:
    pass

无显示结果

 

四、存储数据

1、写入数据

import json
number=[2,3,5,7,11,13]
filename='../data/number.json'
with open(filename,'w') as f:
    json.dump(number,f)

查看结果(number.json)

[2, 3, 5, 7, 11, 13]

2、读取数据

filename='../data/number.json'
with open(filename) as f:
    numbers=json.load(f)
print(numbers)

查看结果：

[2, 3, 5, 7, 11, 13]

3、json+input：保存和读取用户输入

username=input("What is your name?")
filename='username.json'
with open(filename,'w') as f:
    json.dump(username,f)
    print(f"We'll remember you when you come back,{username}!")
with open(filename) as f:
    username=json.load(f)
    print(f"Welcom back,{username}")

查看结果：

What is your name?mike
We'll remember you when you come back,mike!
Welcom back,mike

4、封装用户输入与存储

def get_stored_username():
    """当没有错误时读取保存的用户名"""
    filename='username.json'
    try:
        with open(filename) as f:
            username=json.load(f)
    except FileNotFoundError:
        return None
    else:
        return username

def get_new_username():
    """验证新用户名"""
    username=input("What is your name?")
    filename='username.json'
    with open(filename,'w') as f:
        json.dump(username,f)
    return username

def greet_user():
    """greet the user by name"""
    username=get_stored_username()
    if username:
        print(f"Welcome back,{username}!")
    else:
        username=get_new_username()
        print(f"We will remember you when you come back,{username}!")

greet_user()

查看运行结果：

Welcome back,mike!