try语句的可选else子句的预期用途是什么?
当前回答
也许它的用法是:
#debug = []
def debuglog(text, obj=None):
" Simple little logger. "
try:
debug # does global exist?
except NameError:
pass # if not, don't even bother displaying
except:
print('Unknown cause. Debug debuglog().')
else:
# debug does exist.
# Now test if you want to log this debug message
# from caller "obj"
try:
if obj in debug:
print(text) # stdout
except TypeError:
print('The global "debug" flag should be an iterable.')
except:
print('Unknown cause. Debug debuglog().')
def myfunc():
debuglog('Made it to myfunc()', myfunc)
debug = [myfunc,]
myfunc()
也许这对你也有帮助。
其他回答
下面是我喜欢使用这种模式的另一个地方:
while data in items:
try
data = json.loads(data)
except ValueError as e:
log error
else:
# work on the `data`
就是这样。try-except子句中的'else'块用于当(且仅当)被试操作成功时运行的代码。它可以被利用,也可以被滥用。
try:
fp= open("configuration_file", "rb")
except EnvironmentError:
confdata= '' # it's ok if the file can't be opened
else:
confdata= fp.read()
fp.close()
# your code continues here
# working with (possibly empty) confdata
就我个人而言,我喜欢它,并在适当的时候使用它。它在语义上对语句进行分组。
try:
statements # statements that can raise exceptions
except:
statements # statements that will be executed to handle exceptions
else:
statements # statements that will be executed if there is no exception
例子:
try:
age=int(input('Enter your age: '))
except:
print ('You have entered an invalid value.')
else:
if age <= 21:
print('You are not allowed to enter, you are too young.')
else:
print('Welcome, you are old enough.')
输出:
>>>
Enter your age: a
You have entered an invalid value.
>>> RESTART
>>>
Enter your age: 25
Welcome, you are old enough.
>>> RESTART
>>>
Enter your age: 13
You are not allowed to enter, you are too young.
>>>
复制自:https://geek-university.com/python/the-try-except-else-statements/
else:块令人困惑并且(几乎)毫无用处。它也是for和while语句的一部分。
实际上,即使在if语句中,else:也可能被滥用,造成非常难以发现的错误。
考虑这一点。
if a < 10:
# condition stated explicitly
elif a > 10 and b < 10:
# condition confusing but at least explicit
else:
# Exactly what is true here?
# Can be hard to reason out what condition is true
三思而后行。这通常是个问题。除非在if语句中,否则避免使用它,即使在if语句中,也要考虑记录else-条件,使其显式。
一种用法:测试一些应该引发异常的代码。
try:
this_should_raise_TypeError()
except TypeError:
pass
except:
assert False, "Raised the wrong exception type"
else:
assert False, "Didn't raise any exception"
(在实践中,这段代码应该被抽象为更通用的测试。)
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