[Tutor] exceptions

[Lloyd Kvam]

Here is the "check value" code for numeric input in my current project.
All values that are set from the user interface funnel through here.  I
pulled out the numeric part because I think it is a reasonably complete
example for catching errors.  Part of the process is to build a string
with useful information when something goes wrong to provide some context
in describing the error - as opposed to simply reporting "Invalid Value!"

def uicheckSet(self, fieldname, value):
	''' Raise an exception for invalid value for this fieldname
	'''	
	process = self.uigetProcess( fieldname)	# i keep dictionary of processing info for each fieldname
	...	# skipping to numeric section
	elif process in ['ui_integer', 'ui_money', 'ui_percent', 'ui_year']:
		if not value:		# value may not have come directly from user typing
			value = 0		# so we "rationalize" it
		value = str( value).strip()	
		if process == 'ui_money': regexp = '[-]?[0-9]*\.?[0-9]?[0-9]?'
		elif process == 'ui_percent': regexp = '[-]?[0]*[.][0-9]+'
		else: regexp = '[-]?[0-9]+'
		try:
			m = re.match( regexp, value)
			if not m:
				msg = "Invalid characters for field: %s.  Received: %s.  Valid set is: %s" % (fieldname,value,regexp)
				raise ValueError, msg
			elif m.group() != value:
				msg = "Invalid character %s.  Valid charaters: %s" % (value[m.end()],regexp)
				raise ValueError, msg
		except re.error, diag:
			raise ValueError, str(diag)
		else:
			if process == 'ui_integer': value = int(value)
			else: value = float(value)
			range = self.uigetInput( fieldname)		# here i get the valid range for this fieldname
			if not range[0] <= value <= range[1]:
				raise ValueError, '%s should be between %s and %s' % (fieldname, str(range[0]), str(range[1]))

After this, the fieldname will be set to the supplied value, and if all goes
well, stored in the database.

Cameron Stoner wrote:

> Hi all,
> 
>  
> 
> How do you approach error trapping and use exceptions in Python to take 
> care of it?  How do you for all the possible dumb user mistakes?  I mean 
> give me the kind of thought process of how I should go about thinking 
> this through in planning my program.
> 
>  
> 
> Thanks guys for your help,
> 
>  
> 
> Cameron Stoner
> 


-- 
Lloyd Kvam
Venix Corp.
1 Court Street, Suite 378
Lebanon, NH 03766-1358

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603-443-6155
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801-459-9582