文件和异常

打开文件

with open('pi_digits.txt') as file_object: 
    contents = file_object.read() 
     print(contents)

with关键词可以在不使用文件时自动关闭文件.
open('pi_digits.txt')返回了一个对象,用别名file_object表示.
文件在程序当前目录可不用路径,否则用相对路径或绝对路径表示.
read()函数读取文件中的全部内容,并储存到变量contents里.

逐行读取

filename = 'pi_digits.txt' 
with open(filename) as file_object:
     for line in file_object: 
        print(line)

将每行内容储存成列表可用函数readlines(),例如

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

写入文件

关键是open()函数,第二个实参有三种,读取模式('r'), 写入模式('w'), 附加模式('a')或让你能够读取和写入文件的模式('r+'). 如果你省略了模式实参,Python将以默认的只读模式打开文件。

with open('a.txt','w') as file_object:
    file_object.write("我是哇哈哈!")

with open('a.txt','w') as file_object:
    numbers=" "
    for number in range(1,100000):
        numbers+=str(number)+" "
    file_object.write(numbers)

异常

如下,print(5/0)抛出ZeroDivisionError异常，而except告诉python遇到这种异常该怎么办.

try:
    print(5/0)
except ZeroDivisionError:
    print("数值为0.")

或者这样，没发生错误时走else。

try:
    answer = int(first_number) / int(second_number)
except ZeroDivisionError: 
    print("You can't divide by 0!")
else:
    print(answer)

文件异常是FileNotFoundError，很生动形象。