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
'''
hello world
I love you
How are you?
f = open('files/readme.txt', 'r')
try:
data = f.read()
except:
print('抛出异常')
finally:
f.close()
with open('files/readme.txt', 'r') as f:
data = f.read()
print(data)
hello world
I love you
How are you?
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()
__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
50 - 得到文件中出现频率最高的字符