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-   -   Why Python allows comparison of a callable and a number? (http://www.velocityreviews.com/forums/t706174-why-python-allows-comparison-of-a-callable-and-a-number.html)

一首诗 11-22-2009 12:03 PM

Why Python allows comparison of a callable and a number?
 
I used python to write an assignment last week, here is a code snippet

#================================

def departTime():
'''
Calculate the time to depart a packet.
'''
if(random.random < 0.8):
t = random.expovariate(1.0 / 2.5)
else:
t = random.expovariate(1.0 / 10.5)
return t

#================================

Can you see the problem? I compare random.random with 0.8, which
should be random.random().

Of course this because of my careless, but I don't get it. In my
opinion, this kind of comparison should invoke a least a warning in
any programming language.

So why does python just ignore it?

Chris Rebert 11-22-2009 12:09 PM

Re: Why Python allows comparison of a callable and a number?
 
On Sun, Nov 22, 2009 at 4:03 AM, 一首诗 <newptcai@gmail.com> wrote:
> I used python to write an assignment last week, here is a code snippet
>
> #================================
>
> def departTime():
> * *'''
> * *Calculate the time to depart a packet.
> * *'''
> * *if(random.random < 0.8):
> * * * *t = random.expovariate(1.0 / 2.5)
> * *else:
> * * * *t = random.expovariate(1.0 / 10.5)
> * *return t
>
> #================================
>
> Can you see the problem? *I compare random.random with 0.8, *which
> should be random.random().
>
> Of course this because of my careless, but I don't get it. *In my
> opinion, this kind of comparison should invoke a least a warning in
> any programming language.
>
> So why does python just ignore it?


It's an historical anomaly that's been rectified in Python 3, where
such non-equality comparisons between unrelated types *do* now raise
an error.

Cheers,
Chris
--
http://blog.rebertia.com

MRAB 11-22-2009 04:23 PM

Re: Why Python allows comparison of a callable and a number?
 
一首诗 wrote:
> I used python to write an assignment last week, here is a code snippet
>
> #================================
>
> def departTime():
> '''
> Calculate the time to depart a packet.
> '''
> if(random.random < 0.8):
> t = random.expovariate(1.0 / 2.5)
> else:
> t = random.expovariate(1.0 / 10.5)
> return t
>
> #================================
>
> Can you see the problem? I compare random.random with 0.8, which
> should be random.random().
>
> Of course this because of my careless, but I don't get it. In my
> opinion, this kind of comparison should invoke a least a warning in
> any programming language.
>
> So why does python just ignore it?


In Python 2 you can compare any 2 objects, for example an int with a
string. The result is arbitrary but consistent.

In Python 3 if the 2 objects aren't 'compatible' you'll get a TypeError
at runtime.

BTW, you don't need to put parentheses around the conditions in 'if' and
'while' statements. Python isn't C, etc. :-)


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