Christian: While Python is type agnostic, most databases are pretty fussy about what you feed them. I presume that you need to convert the user's data into a form acceptable to the database. You do not specify what tool you are using to write your results to the database, so I will provide several answers to your question... 1) If you are writing to the database using Python, and you are using a fully PEP 249 compliant database module: The database module should attempt the conversion for you, giving an exception if it cannot. You will need to do the most obvious conversions yourself such as making a number into a string, so an "if" "except" construct should do handily. As far as I know, only the adodbapi module is both fully PEP 249 compliant and implemented in IronPython. http://sourceforge.net/projects/adodbapi 2) You can use Python's "isinstance" built in function to see what the user sent you: <code> impert types a = theOutputFromYourUser() if isinstance(a,types.StringType): print "it was a string" if isinstance(a, (types.FloatType, types.IntType)): print "it was a number" </code> 3) You can take advantage of python's "duck type" capability by simply trying the user's output to see if it will work as a given type... <code> numericResult = None stringResult = None a = theOutputFromYourUser() try: numericResult = float(a) except: try: stringResult = str(a) except: pass if numericResult != None: # your numeric stuff here elif stringResult != None: # your string stuff here else: # your error handling here. </code> 4) Use some combination of the above. For example: adodbapi uses a dictionary dispatch table to chose which conversion to call, which is a variation on option 2, but then uses exception handling to catch errors within the specific code for some conversions. YMMV -- Vernon Cole
On Mon, Oct 19, 2009 at 5:20 AM, Michael Foord <fuzzy...@voidspace.org.uk>wrote: > Christian Schmidt wrote: > >> Hello, >> >> we are using IronPython embedded into our application to evaluate user >> defined expression. The "variables" used in the expressions are strongly >> typed and the results need to be written back into a database. >> >> I know that the return type of a dynamic expression cannot be determined >> in general. But what would be a pragmatic way to guess the return type >> of an expression? >> > > Hehe. If you're evaluating arbitrary functions provided by the user then I > don't know of any way of 'inferring' the return type - beyond parsing it and > modelling the type flow through the expression (which would be a lot of > work). > > All the best, > > Michael > >> >> Thanks, >> Christian >> >> >> >> _______________________________________________ >> Users mailing list >> Users@lists.ironpython.com >> http://lists.ironpython.com/listinfo.cgi/users-ironpython.com >> > > > -- > http://www.ironpythoninaction.com/ > http://www.voidspace.org.uk/blog > > > > _______________________________________________ > Users mailing list > Users@lists.ironpython.com > http://lists.ironpython.com/listinfo.cgi/users-ironpython.com >
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