Re: try-except syntax

[ElChino]

Steven D'Aprano wrote:


imp.find_module is deprecated and should not be used in new code.

...


 try:
   block
 except (ImportError, RuntimeError):
   block


Thanks Steven and others who replied. Looks more elegant.


By the way, RuntimeError is almost never something you want to catch
(except to log before bailing out). It should represent a fatal coding
error, not something safe to ignore.


I was simply playing around with 'imp'. Hence I blocked
RuntimeError.

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Re: try-except syntax

[Steven D'Aprano]

On Thu, 05 Apr 2018 23:04:18 +0200, ElChino wrote:

> I'm trying to simplify a try-except construct. E.g. how come this:
>try:
>  _x, pathname, _y = imp.find_module (mod, mod_path)
>  return ("%s" % pathname)

imp.find_module is deprecated and should not be used in new code.

Putting that aside, pathname is already a string. Why are you wasting 
time interpolating it into a bare "%s" string? Just say `return pathname`.


>except ImportError:
>  pass
>except RuntimeError:
>  pass
>  return ("")

Unnecessary parens surrounding a single value.

Possible indentation error. Surely the return "" needs to be 
indented level with the try/except statements?


> Cannot be simplified into this:
>try:
>  _x, pathname, _y = imp.find_module (mod, mod_path) return ("%s" %
>  pathname)
>except ImportError:
>except RuntimeError:
>  pass
>  return ("")
> 
> Like a "fall-through" in a C-switch statement.

Because fall-through C switch syntax is an abomination, and fortunately 
the designer of Python has more sense than to allow that awfulness.


The syntax you are looking for is:


try:
  block
except (ImportError, RuntimeError):
  block



By the way, RuntimeError is almost never something you want to catch 
(except to log before bailing out). It should represent a fatal coding 
error, not something safe to ignore.


-- 
Steve

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Re: try-except syntax

[Gregory Ewing]

Ben Bacarisse wrote:

Anyway, to coalesce two or more exception handlers, you are probably
looking for

  except (ImportError, RuntimeError):


To the OP: Are you sure you really want to mask RuntimeError here?
Usually it means something has gone seriously wrong, and is a
symptom that shouldn't be ignored.

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Greg
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Re: try-except syntax

[Ben Bacarisse]

ElChino  writes:

> I'm trying to simplify a try-except construct. E.g. how come
> this:
>   try:
> _x, pathname, _y = imp.find_module (mod, mod_path)
> return ("%s" % pathname)
>   except ImportError:
> pass
>   except RuntimeError:
> pass
> return ("")
>
> Cannot be simplified into this:
>   try:
> _x, pathname, _y = imp.find_module (mod, mod_path)
> return ("%s" % pathname)
>   except ImportError:
>   except RuntimeError:
> pass
> return ("")
>
> Like a "fall-through" in a C-switch statement.

The except parts don't fall through, and each one needs a "suite".
Also, the "pass" before the return is mysterious which makes me think
there's an indent error in what you posted.

Anyway, to coalesce two or more exception handlers, you are probably
looking for

  except (ImportError, RuntimeError):

which matches both.

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Ben.
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Re: try-except syntax

[Ian Kelly]

On Thu, Apr 5, 2018 at 3:04 PM, ElChino  wrote:
> I'm trying to simplify a try-except construct. E.g. how come
> this:
>   try:
> _x, pathname, _y = imp.find_module (mod, mod_path)
> return ("%s" % pathname)
>   except ImportError:
> pass
>   except RuntimeError:
> pass
> return ("")
>
> Cannot be simplified into this:
>   try:
> _x, pathname, _y = imp.find_module (mod, mod_path)
> return ("%s" % pathname)
>   except ImportError:
>   except RuntimeError:
> pass
> return ("")
>
> Like a "fall-through" in a C-switch statement.

You're looking for:

  try:
_x, pathname, _y = imp.find_module (mod, mod_path)
return ("%s" % pathname)
  except (ImportError, RuntimeError):
return ("")
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Re: try-except syntax

[Rob Gaddi]

On 04/05/2018 02:04 PM, ElChino wrote:

I'm trying to simplify a try-except construct. E.g. how come
this:
   try:
     _x, pathname, _y = imp.find_module (mod, mod_path)
     return ("%s" % pathname)
   except ImportError:
     pass
   except RuntimeError:
     pass
     return ("")

Cannot be simplified into this:
   try:
     _x, pathname, _y = imp.find_module (mod, mod_path)
     return ("%s" % pathname)
   except ImportError:
   except RuntimeError:
     pass
     return ("")

Like a "fall-through" in a C-switch statement.


try:
  _x, pathname, _y = imp.find_module (mod, mod_path)
  return ("%s" % pathname)
except (ImportError, RuntimeError):
  pass
  return ("")

That handles the identical case.  C-style fall-throughs where you have 
one switch have just a bit of code before the fall-through kicks in (the 
slightly non-identical case) is often the source of disastrous code errors.


--
Rob Gaddi, Highland Technology -- www.highlandtechnology.com
Email address domain is currently out of order.  See above to fix.
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try-except syntax

[ElChino]

I'm trying to simplify a try-except construct. E.g. how come
this:
  try:
_x, pathname, _y = imp.find_module (mod, mod_path)
return ("%s" % pathname)
  except ImportError:
pass
  except RuntimeError:
pass
return ("")

Cannot be simplified into this:
  try:
_x, pathname, _y = imp.find_module (mod, mod_path)
return ("%s" % pathname)
  except ImportError:
  except RuntimeError:
pass
return ("")

Like a "fall-through" in a C-switch statement.
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