[Pythonmac-SIG] Baffling if statement

[Bob Ippolito]

On Sep 22, 2005, at 3:34 PM, Kirk Durston wrote:

> After spending a couple hours trying to figure out what is going  
> on, I’m asking for help.
>
> Below is a short segment from a module I’ve written. Before the  
> part shown below, temp and Cutoff are defined. then comes the  
> following:
>
>             blank='-'
>             if temp>Cutoff:
>                 print 'temp is', temp
>                 print 'cutoff is', Cutoff
>                 print 'symbol is', symbol
>                 InfoCollector.append(symbol)
>             else:InfoCollector.append(blank)
>
> the print out shows that temp=0.261 and Cutoff is 0.29498. Clearly  
> temp is smaller than Cutoff, so it should have gone to ‘else:’ but  
> it didn’t. In fact, no matter if temp is larger or smaller than  
> Cutoff, it always goes through the ‘if’ segment.

Sounds like you're comparing a float and a string.  Don't do that,  
make sure that temp and cutoff are both float if you expect a  
meaningful comparison.

To convert a string to a float, use float(aString).

To see the "programmer representation" of a variable, use the %r  
format string, or the repr() function.  E.g.:

print 'temp is', repr(temp)

or

print 'cutoff is %r' % (Cutoff,)

Using programmer repr[esentations] for debugging is essential, the  
string representations of types can be (intentionally) ambiguous.

One of the two is almost definitely a string, so you should do temp =  
float(temp) or similar.

-bob

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