除了块之外的打印语句答案

【问题标题】：print statement outside except block除了块之外的打印语句
【发布时间】：2020-08-17 13:32:23
【问题描述】：

import sys
lst = ['b', 0, 2,5]
for entry in lst:
  try:
    print("****************************")
    print("The entry is", entry)
    r = 1 / int(entry)
  except(ValueError):
    print("This is a ValueError.")
  except(ZeroDivisionError):
    print("This is a ZeroError.")
  except:
    print("Some other error")
print("The reciprocal of", entry, "is", r)

当程序将输入作为 2 时，除了块之外的打印语句将被跳过。但如果我只在列表中给出 3 个元素，它就可以正常工作。

【问题讨论】：

标签： python try-except

【解决方案1】：

这是因为 print 语句在 for 循环之外。所以它只打印entry 的最后一次迭代。

检查一下：

In [1340]: import sys 
      ...: lst = ['b'] 
      ...: for entry in lst: 
      ...:   try: 
      ...:     print("****************************") 
      ...:     print("The entry is", entry) 
      ...:     r = 1 / int(entry) 
      ...:   except(ValueError): 
      ...:     print("This is a ValueError.") 
      ...:   except(ZeroDivisionError): 
      ...:     print("This is a ZeroError.") 
      ...:   except: 
      ...:     print("Some other error") 
      ...: print("The reciprocal of", entry, "is", r)
****************************
The entry is b
This is a ValueError.
The reciprocal of b is 0.2

如果您希望它为每个元素打印，请将打印推入 for 循环：

In [1344]: import sys 
      ...: lst = ['b',0,2,5] 
      ...: for entry in lst: 
      ...:   try: 
      ...:     print("****************************") 
      ...:     print("The entry is", entry) 
      ...:     r = 1 / int(entry) 
      ...:   except(ValueError): 
      ...:     print("This is a ValueError.") 
      ...:   except(ZeroDivisionError): 
      ...:     print("This is a ZeroError.") 
      ...:   except: 
      ...:     print("Some other error") 
      ...:   else: 
      ...:     print("The reciprocal of", entry, "is", r) 
      ...:                                                                                                                                                                                                  
****************************
The entry is b
This is a ValueError.
****************************
The entry is 0
This is a ZeroError.
****************************
The entry is 2
The reciprocal of 2 is 0.5
****************************
The entry is 5
The reciprocal of 5 is 0.2

【讨论】：

【解决方案2】：

由于您的print 位于for 循环之外，因此它仅在循环的最后一次迭代之后执行，即5 值。您需要将其放入循环中，但将其放入 try 的 else 子句中，以便仅在没有发生异常时执行：

import sys
lst = ['b', 0, 2,5]
for entry in lst:
  try:
    print("****************************")
    print("The entry is", entry)
    r = 1 / int(entry)
  except(ValueError):
    print("This is a ValueError.")
  except(ZeroDivisionError):
    print("This is a ZeroError.")
  except:
    print("Some other error")
  else:
    print("The reciprocal of", entry, "is", r)

输出：

****************************
The entry is b
This is a ValueError.
****************************
The entry is 0
This is a ZeroError.
****************************
The entry is 2
The reciprocal of 2 is 0.5
****************************
The entry is 5
The reciprocal of 5 is 0.2

【讨论】：

【解决方案3】：

lst = ['b', 0, 2, 5]
for entry in lst:
  try:
    print("****************************")
    print("The entry is", entry)
    r = 1 / int(entry)
    print("The reciprocal of", entry, "is", r)
  except(ValueError):
    print("This is a ValueError.")
  except(ZeroDivisionError):
    print("This is a ZeroError.")
  except:
    print("Some other error")

print 语句应该在 try 块内

【讨论】：