about try statement

[Shi Mu]

very hard for me to understand the difference between
try...except and try...finally

 

[Sybren Stuvel]

Shi Mu enlightened us with:

very hard for me to understand the difference between try...except
and try...finally

Within a 'try' block, if an exception is called and a matching
'except' block is found, that block will be used to handle the
expression.

From the documentation of the "return" keyword: "When return passes
control out of a try statement with a finally clause, that finally
clause is executed before really leaving the function." Note that
there is no talk about exceptions in this.

Sybren

 

[Bengt Richter]

Shi Mu enlightened us with:

Within a 'try' block, if an exception is called and a matching
'except' block is found, that block will be used to handle the
expression.

From the documentation of the "return" keyword: "When return passes
control out of a try statement with a finally clause, that finally
clause is executed before really leaving the function." Note that
there is no talk about exceptions in this.

Which is because in the finally block the exception is still "live"
and will take effect as soon as the finally block is left, e.g.,
... try: 1/0
... finally: print 'exception can not bypass finally'
... except Exception, e:
... print '%s: %s' %(e.__class__.__name__, e)
...
exception can not bypass finally
ZeroDivisionError: integer division or modulo by zero

Or to make the point about return ... try:
... try: return 1/den
... finally: print 'exception can not bypass finally'
... except Exception, e:
... print '%s: %s' %(e.__class__.__name__, e)
... return 'succeeded in returning something'
... exception can not bypass finally
ZeroDivisionError: integer division or modulo by zero
'succeeded in returning something' exception can not bypass finally
1

Regards,
Bengt Richter