Best way to generate alternate toggling values in a loop?

[Debajit Adhikary]

I'm writing this little Python program which will pull values from a
database and generate some XHTML.

I'm generating a <tablewhere I would like the alternate <tr>'s to be

<tr class="Even">
and
<tr class="Odd">

What is the best way to do this?

I wrote a little generator (code snippet follows). Is there a better
(more "Pythonic") way to do this?


# Start of Code

def evenOdd():
values = ["Even", "Odd"]
state = 0
while True:
yield values[state]
state = (state + 1) % 2


# Snippet

trClass = evenOdd()
stringBuffer = cStringIO.Strin gIO()

for id, name in result:
stringBuffer.wr ite('''
<tr class="%s">
<td>%d</td>
<td>%s</td>
</tr>
'''
%
(trClass.next() , id, name))


# End of Code

[Carsten Haese]

Re: Best way to generate alternate toggling values in a loop?

On Wed, 2007-10-17 at 23:55 +0000, Debajit Adhikary wrote:

I'm writing this little Python program which will pull values from a
database and generate some XHTML.
>
I'm generating a <tablewhere I would like the alternate <tr>'s to be
>
<tr class="Even">
and
<tr class="Odd">
>
What is the best way to do this?
>
I wrote a little generator (code snippet follows). Is there a better
(more "Pythonic") way to do this?
>
>
# Start of Code
>
def evenOdd():
values = ["Even", "Odd"]
state = 0
while True:
yield values[state]
state = (state + 1) % 2
>
>
# Snippet
>
trClass = evenOdd()
stringBuffer = cStringIO.Strin gIO()
>
for id, name in result:
stringBuffer.wr ite('''
<tr class="%s">
<td>%d</td>
<td>%s</td>
</tr>
'''
%
(trClass.next() , id, name))

This is a respectable first attempt, but I recommend you familiarize
yourself with the itertools module. It has lots of useful tools for
making your code more elegant and concise.

Rather than spelling out the final result, I'll give you hints: Look at
itertools.cycle and itertools.izip.

HTH,

--
Carsten Haese

http://informixdb.sourceforge.net

[Grant Edwards]

Re: Best way to generate alternate toggling values in a loop?

On 2007-10-17, Debajit Adhikary <debajit1@gmail .comwrote:

# Start of Code
>
def evenOdd():
values = ["Even", "Odd"]
state = 0
while True:
yield values[state]
state = (state + 1) % 2

I'd replace the last line with

state ^= 1

to save a couple instructions, but I spend too much time
working with micoroprocessor s running on clocks measured in the
KHz.

There are probably other more Pythonic ways...

--
Grant Edwards grante Yow! My EARS are GONE!!
at
visi.com

[Gerard Flanagan]

Re: Best way to generate alternate toggling values in a loop?

On Oct 18, 1:55 am, Debajit Adhikary <debaj...@gmail .comwrote:

I'm writing this little Python program which will pull values from a
database and generate some XHTML.
>
I'm generating a <tablewhere I would like the alternate <tr>'s to be
>
<tr class="Even">
and
<tr class="Odd">
>
What is the best way to do this?
>

from itertools import izip

def toggle(start=Tr ue):
flag = start
while 1:
flag = not flag
yield flag


CSS = ("even", "odd")

HTML = '<tr class="%s"><td> %d</td><td>%s</td></tr>'

result = [(1, 'One'), (2, 'two'), (3, 'Three'), (4, 'Four'), (5,
'Five')]

for flag, (id, name) in izip(toggle(), result):
print HTML % (CSS[flag], id, name)


<tr class="even"><t d>1</td><td>One</td></tr>
<tr class="odd"><td >2</td><td>two</td></tr>
<tr class="even"><t d>3</td><td>Three</td></tr>
<tr class="odd"><td >4</td><td>Four</td></tr>
<tr class="even"><t d>5</td><td>Five</td></tr>

[Amit Khemka]

Re: Best way to generate alternate toggling values in a loop?

On 10/18/07, Carsten Haese <carsten@uniqsy s.comwrote:

On Wed, 2007-10-17 at 23:55 +0000, Debajit Adhikary wrote:

I'm writing this little Python program which will pull values from a
database and generate some XHTML.

I'm generating a <tablewhere I would like the alternate <tr>'s to be

<tr class="Even">
and
<tr class="Odd">

What is the best way to do this?

I wrote a little generator (code snippet follows). Is there a better
(more "Pythonic") way to do this?


# Start of Code

def evenOdd():
values = ["Even", "Odd"]
state = 0
while True:
yield values[state]
state = (state + 1) % 2


# Snippet

trClass = evenOdd()
stringBuffer = cStringIO.Strin gIO()

for id, name in result:
stringBuffer.wr ite('''
<tr class="%s">
<td>%d</td>
<td>%s</td>
</tr>
'''
%
(trClass.next() , id, name))

>
This is a respectable first attempt, but I recommend you familiarize
yourself with the itertools module. It has lots of useful tools for
making your code more elegant and concise.
>
Rather than spelling out the final result, I'll give you hints: Look at
itertools.cycle and itertools.izip.
>

Why not just use enumerate ?

clvalues = ["Even", "Odd"]
for i, (id, name) in enumerate(resul t):
stringBuffer.wr ite('''
<tr class="%s">
<td>%d</td>
<td>%s</td>
</tr>
'''
%
(clvalues[i % 2], id, name))

Cheers,

--
--
Amit Khemka

[Paul Hankin]

Re: Best way to generate alternate toggling values in a loop?

On Oct 18, 12:11 pm, "Amit Khemka" <khemkaa...@gma il.comwrote:

On 10/18/07, Carsten Haese <cars...@uniqsy s.comwrote:

Rather than spelling out the final result, I'll give you hints: Look at
itertools.cycle and itertools.izip.

>
Why not just use enumerate ?
>
clvalues = ["Even", "Odd"]
for i, (id, name) in enumerate(resul t):
stringBuffer.wr ite('''
<tr class="%s">
<td>%d</td>
<td>%s</td>
</tr>
'''
%
(clvalues[i % 2], id, name))

I like this code: straightforward and pragmatic. Everyone else seems
to be reinventing itertools.cycle - they should have listened to
Carsten, and written something like this:

import itertools

clvalues = itertools.cycle (['Even', 'Odd'])
for clvalue, (id, name) in itertools.izip( clvalues, result):
stringBuffer.wr ite('''
<tr class="%(name)s ">
<td>%(id)d</td>
<td>%(clvalue)s </td>
</tr>''' % locals())

--
Paul Hankin

[Grant Edwards]

Re: Best way to generate alternate toggling values in a loop?

On 2007-10-18, Gerard Flanagan <grflanagan@yah oo.co.ukwrote:

On Oct 18, 1:55 am, Debajit Adhikary <debaj...@gmail .comwrote:

>I'm writing this little Python program which will pull values from a
>database and generate some XHTML.
>>
>I'm generating a <tablewhere I would like the alternate <tr>'s to be
>>
><tr class="Even">
>and
><tr class="Odd">
>>
>What is the best way to do this?
>>

>
>
from itertools import izip
>
def toggle(start=Tr ue):
flag = start
while 1:
flag = not flag
yield flag

I like the solution somebody sent me via PM:

def toggle():
while 1:
yield "Even"
yield "Odd"

--
Grant Edwards grante Yow! Are we THERE yet?
at
visi.com

[Alex Martelli]

Re: Best way to generate alternate toggling values in a loop?

Grant Edwards <grante@visi.co mwrote:
...

I like the solution somebody sent me via PM:
>
def toggle():
while 1:
yield "Even"
yield "Odd"

I think the itertools-based solution is more elegant:

toggle = itertools.cycle (('Even', 'Odd'))

and use toggle rather than toggle() later; or, just use that
itertools.cycle call inside the expression instead of toggle().


Alex

[Iain King]

Re: Best way to generate alternate toggling values in a loop?

On Oct 18, 2:29 am, Grant Edwards <gra...@visi.co mwrote:

On 2007-10-17, Debajit Adhikary <debaj...@gmail .comwrote:
>

# Start of Code

>

def evenOdd():
values = ["Even", "Odd"]
state = 0
while True:
yield values[state]
state = (state + 1) % 2

>
I'd replace the last line with
>
state ^= 1
>
to save a couple instructions, but I spend too much time
working with micoroprocessor s running on clocks measured in the
KHz.
>
There are probably other more Pythonic ways...
>

I always use:

state = 1 - state

for toggles. I doubt it's much more pythonic though :)

Iain

[cokofreedom@gmail.com]

Re: Best way to generate alternate toggling values in a loop?

On Oct 18, 3:48 pm, Iain King <iaink...@gmail .comwrote:

On Oct 18, 2:29 am, Grant Edwards <gra...@visi.co mwrote:
>
>
>

On 2007-10-17, Debajit Adhikary <debaj...@gmail .comwrote:

>

# Start of Code

>

def evenOdd():
values = ["Even", "Odd"]
state = 0
while True:
yield values[state]
state = (state + 1) % 2

>

I'd replace the last line with

>

state ^= 1

>

to save a couple instructions, but I spend too much time
working with micoroprocessor s running on clocks measured in the
KHz.

>

There are probably other more Pythonic ways...

>
I always use:
>
state = 1 - state
>
for toggles. I doubt it's much more pythonic though :)
>
Iain

why not do
state = not state
?

[Luis Zarrabeitia]

Re: Best way to generate alternate toggling values in a loop?

On Thursday 18 October 2007 09:09, Grant Edwards wrote:

I like the solution somebody sent me via PM:
>
def toggle():
while 1:
yield "Even"
yield "Odd"
>

That was me.
Sorry, list, I meant to send it to everyone but I my webmail didn't respect
the list* headers :(.

Thanks, Grant!

--
Luis Zarrabeitia (aka Kyrie)
Fac. de Matemática y Computación, UH.

http://profesores.matcom.uh.cu/~kyrie