1. with语句有什么作用，请用代码解释

• with语句适用于对资源访问的场合，确保不管使用过程是否发生异常都会执行必要的 "清理"工作

f = open('files/readme.txt', 'r')
data = f.read()
print(data)

'''
1. 没有关闭文件
2. 即使关闭了文件，但在关闭之前如果抛出异常，仍然会无法关闭文件
'''

  
 

  
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hello world
I love you
How are you?

  
 

  
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f = open('files/readme.txt', 'r')
try: data = f.read()
except: print('抛出异常')
finally: f.close()

  
 

  
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with open('files/readme.txt', 'r') as f: data = f.read() print(data)

  
 

  
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hello world
I love you
How are you?

  
 

  
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2. 如何将with语句用于一个自定义类

'''
__enter__

__exit__
'''

class MyClass: def __enter__(self): print('__enter__() is call!') return self def process1(self): print('process1') def process2(self): x = 1/0 print('process2') def __exit__(self, exc_type, exc_value, traceback): print('__exit__() is call!') print(f'type:{exc_type}') print(f'value:{exc_value}') print(f'trace:{traceback}') with MyClass() as my: my.process1() my.process2()

  
 

  
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__enter__() is call!
process1
__exit__() is call!
type:<class 'ZeroDivisionError'>
value:division by zero
trace:<traceback object at 0x0000029AA9F98DC8> ---------------------------------------------------------------------------

ZeroDivisionError Traceback (most recent call last)

<ipython-input-10-b97c97f6e5f0> in <module> 23 with MyClass() as my: 24 my.process1()
---> 25 my.process2()
<ipython-input-10-b97c97f6e5f0> in process2(self) 13 14 def process2(self):
---> 15 x = 1/0 16 print('process2') 17 def __exit__(self, exc_type, exc_value, traceback):
ZeroDivisionError: division by zero

  
 

  
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50 - 得到文件中出现频率最高的字符

文章来源: ruochen.blog.csdn.net，作者：若尘，版权归原作者所有，如需转载，请联系作者。

原文链接：ruochen.blog.csdn.net/article/details/104674824