为什么python中的try语句需要else子句？ [英] Why is else clause needed for try statement in python?

问题描述

在Python中，try语句支持一个else子句，如果try块中的代码不引发异常，它将执行。例如：

In Python the try statement supports an else clause, which executes if the code in try block does not raise an exception. For example:

try:
  f = open('foo', 'r')
except IOError as e:
  error_log.write('Unable to open foo : %s\n' % e)
else:
  data = f.read()
  f.close()

为什么需要else子句？我们不能写上面的代码如下：

Why is the else clause needed? Can't we write the above code as follows :

try:
  f = open('foo', 'r')
  data = f.read()
  f.close()
except IOError as e:
  error_log.write('Unable to open foo : %s\n' % e)

执行不会继续到 data = f。 read（）如果打开不引发异常？

Won't the execution proceed to data = f.read() if open does not raise an exception?

推荐答案

区别是如果你在f.read（）或f.close（）代码中收到错误。在这种情况下：

The difference is what happens if you get an error in the f.read() or f.close() code. In this case:

try:
  f = open('foo', 'r')
  data = f.read()
  f.close()
except IOError as e:
  error_log.write('Unable to open foo : %s\n' % e)

f.read（）或 f.close（）在这种情况下会给你日志消息无法打开foo，这显然是错误的。

An error in f.read() or f.close() in this case would give you the log message "Unable to open foo", which is clearly wrong.

在这种情况下，这是避免的：

In this case, this is avoided:

try:
  f = open('foo', 'r')
except IOError as e:
  error_log.write('Unable to open foo : %s\n' % e)
else:
  data = f.read()
  f.close()

读取或关闭的错误不会导致日志写入，但是在调用堆栈中错误会上升。

And error in reading or closing would not cause a log write, but the error would rise uncatched upwards in the call stack.

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