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.StringIO()

for id, name in result:
stringBuffer.write('''
<tr class="%s">
<td>%d</td>
<td>%s</td>
</tr>
'''
%
(trClass.next(), id, name))
# End of Code

[Carsten Haese]

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.StringIO()

for id, name in result:
stringBuffer.write('''
<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]

On 2007-10-17, Debajit Adhikary <de******@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 micoroprocessors 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]

On Oct 18, 1:55 am, Debajit Adhikary <[e-mail]:

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

[Amit Khemka]

On 10/18/07, Carsten Haese <ca*****@uniqsys.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.StringIO()

for id, name in result:
stringBuffer.write('''
<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(result):
stringBuffer.write('''
<tr class="%s">
<td>%d</td>
<td>%s</td>
</tr>
'''
%
(clvalues[i % 2], id, name))

Cheers,

--
--
Amit Khemka

[Paul Hankin]

On Oct 18, 12:11 pm, "Amit Khemka" <[e-mail]:

On 10/18/07, Carsten Haese <[e-mail]:

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(result):
stringBuffer.write('''
<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.write('''
<tr class="%(name)s">
<td>%(id)d</td>
<td>%(clvalue)s</td>
</tr>''' % locals())

--
Paul Hankin

[Grant Edwards]

On 2007-10-18, Gerard Flanagan <gr********@yahoo.co.ukwrote:

On Oct 18, 1:55 am, Debajit Adhikary <[e-mail]:

>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=True):
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]

Grant Edwards <gr****@visi.comwrote:
...

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]

On Oct 18, 2:29 am, Grant Edwards <[e-mail]:

On 2007-10-17, Debajit Adhikary <[e-mail]:

# 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 micoroprocessors 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]

On Oct 18, 3:48 pm, Iain King <[e-mail]:

On Oct 18, 2:29 am, Grant Edwards <[e-mail]:

On 2007-10-17, Debajit Adhikary <[e-mail]:

# 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 micoroprocessors 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]

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