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Exception analysis in python

高洛峰

Mar 08, 2017 am 09:49 AM

python

Each exception is an instance of some class. These instances can be raised and can be caught in many ways, so that the program can catch the error and handle it

>>> 1/0

Traceback (most recent call last):
  File "<pyshell#0>", line 1, in <module>
    1/0
ZeroDivisionError: integer division or modulo by zero

Exception handling

To catch exceptions, you can use the try/except statement.

>>> def inputnum():
    x=input(&#39;Enter the first number: &#39;)
    y=input(&#39;Enter the first number: &#39;)
    try:
        print x/y
    except ZeroDivisionError:
        print "The second number can&#39;t be zero"

        
>>> inputnum()
Enter the first number: 10
Enter the first number: 0
The second number can&#39;t be zero

raise trigger exception

>>> class Muff:
    muffled=False
    def calc(self,expr):
        try:
            return eval(expr)
        except ZeroDivisionError:
            if self.muffled:
                print &#39;Division by zero is illegal&#39;
            else:
                raise

            
>>> c=Muff()
>>> c.calc(10/2)

Traceback (most recent call last):
  File "<pyshell#33>", line 1, in <module>
    c.calc(10/2)
  File "<pyshell#31>", line 5, in calc
    return eval(expr)
TypeError: eval() arg 1 must be a string or code object
>>> c.calc(&#39;10/2&#39;)
>>> c.calc(&#39;1/0&#39;)

Traceback (most recent call last):
  File "<pyshell#35>", line 1, in <module>
    c.calc(&#39;1/0&#39;)
  File "<pyshell#31>", line 5, in calc
    return eval(expr)
  File "<string>", line 1, in <module>
ZeroDivisionError: integer division or modulo by zero
>>> c.muffled=True
>>> c.calc(&#39;1/0&#39;)
Division by zero is illegal

Multiple exception types

try:
    x=input(&#39;Enter the first number:&#39;)
    y=input(&#39;Enter the seconed number:&#39;)
    print x/y
except ZeroDivisionError:
    print "The second number can&#39;t be zero!"
except TypeError:
    print "That wasn&#39;t a number,was it?"

Catch multiple exceptions at the same time

try:
    x=input(&#39;Enter the first number:&#39;)
    y=input(&#39;Enter the seconed number:&#39;)
    print x/y
except(ZeroDivisionError,TypeError,NameError):
    print &#39;Your numbers were bogus...&#39;

Capture object

try:
    x=input(&#39;Enter the first number:&#39;)
    y=input(&#39;Enter the seconed number:&#39;)
    print x/y
except(ZeroDivisionError,TypeError),e:
    print e

    
Enter the first number:1
Enter the seconed number:0
integer division or modulo by zero

Capture All exceptions

try:
    x=input(&#39;Enter the first number:&#39;)
    y=input(&#39;Enter the seconed number:&#39;)
    print x/y
except:
    print &#39;something wrong happened...&#39;

    
Enter the first number:
something wrong happened...

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