[New-bugs-announce] [issue9240] different behaviour with for loop... interpreted vs scripted

Diego Jacobi report at bugs.python.org
Tue Jul 13 02:11:12 CEST 2010


New submission from Diego Jacobi <jacobidiego at gmail.com>:

Hi.
I am not a python expert and i was trying to reduce this next code:

        data = []
        i = 0
        for j in range(packetlen+1):
            print i, self.channels_in[ channels[i] ]
            data.append( self.channels_in[ channels[i] ].pop() )
            i += 1
            if i >= len(channels):
                i=0

into something like this:

        data = []
        for j in range(packetlen+1), i in channels:
            print j, i
            data.append( self.channels_in[ i ].pop() )

which is much more readable and short.
But i didnt know if this sintax is really supported (also i didnt found examples on internet), so i just tried.

I runned the script and it didnt complains with errors, BUT i found that the behavior is not what i expected.

I expected j to take value of range() and i to take the values of channels until range() gets empty.

well, the actual behavior is that j takes the value of the complete range() as in
j = range(..)

and the for loop iterates as in 
for i in channels:


ALSO i tested this un the python command line and it produces different behaviours:

the same sintax writen as:

for j in range(1,5), i in range(120,500,12):
   print j, i

produces 

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'i' is not defined


Thats all. I guess that if it produces different results, then there is an error happening here.


If there is a pythonic way to do this:
for j in range(packetlen+1), i in channels:

please tell me.

Cheers.
Diego

----------
messages: 110150
nosy: jacobidiego
priority: normal
severity: normal
status: open
title: different behaviour with for loop... interpreted vs scripted
type: behavior
versions: Python 2.6

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue9240>
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