for loop without variable

[erik gartz]

Hi. I'd like to be able to write a loop such as:
for i in range(10):
pass
but without the i variable. The reason for this is I'm using pylint
and it complains about the unused variable i. I can achieve the above
with more lines of code like:
i = 0
while (i != 10):
i += 1
Is there a concise way to accomplish this without adding extra lines
of codes? Thanks in advance for your help.

[Mike Meyer]

On Wed, 9 Jan 2008 18:49:36 -0800 (PST) erik gartz <ee******@yahoo .comwrote:

The loop performs some actions with web services. The particular
iteration I'm on isn't important to me. It is only important that I
attempt the web services that number of times. If I succeed I
obviously break out of the loop and the containing function (the
function which has the loop in it) returns True. If all attempts fail
the containing loop returns False.

It sounds to me like your counter variable actually has meaning, but
you've hidden that meaning by giving it the meaningless name "i". If
you give it a meaningful name, then there's an obvious way to do it
(which you listed yourself):

while retries_left:
if this_succeeds() :
return True
retries_left -= 1

return False

<mike
--
Mike Meyer <mw*@mired.or g> http://www.mired.org/consulting.html
Independent Network/Unix/Perforce consultant, email for more information.

[Sam]

Unfortunately, I don't *think* I can shut the
warning for that line or function off, only for the entire file.
Pylint gives you a rating of your quality of code which I think is

wrong :)

# pylint: disable-msg=XXXXX will only impact the current line!

$ cat -n dummy.py
1 for i in range(2): # pylint: disable-msg=W0612
2 print "foo"
3 for i in range(2):
4 print "foo"

pylint will not generate a warning on line 1, but will on line 3!

Cheers.

Sam

[Hrvoje Niksic]

Mike Meyer <mw************ ***********@mir ed.orgwrites:

It sounds to me like your counter variable actually has meaning,

It depends how the code is written. In the example such as:

for meaningless_var iable in xrange(number_o f_attempts):
...

the loop variable really has no meaning. Rewriting this code only to
appease pylint is exactly that, it has nothing with making the code
more readable.

you've hidden that meaning by giving it the meaningless name "i". If
you give it a meaningful name, then there's an obvious way to do it
(which you listed yourself):

while retries_left:

[...]

This loop contains more code and hence more opportunities for
introducing bugs. For example, if you use "continue" anywhere in the
loop, you will do one retry too much.

[Jeroen Ruigrok van der Werven]

-On [20080110 00:21], Ben Finney (bi************ ****@benfinney. id.au) wrote:

>The problem with the '_' name is that it is already well-known and
long-used existing convention for an entirely unrelated purpose: in
the 'gettext' i18n library, the '_' function to get the
locally-translated version of a text string.

The same applies for Babel (http://babel.edgewall.org/) where we have _() in
similar vein to the gettext implementation.

--
Jeroen Ruigrok van der Werven <asmodai(-at-)in-nomine.org/ asmodai
イェルーン ラウフãƒ*ッ ク ヴァン デル ウェルヴェ ン
http://www.in-nomine.org/ | http://www.rangaku.org/
With a nuclear fire of Love in our Hearts, rest easy baby, rest easy...

[Torsten Bronger]

Hallöchen!

Ben Finney writes:

"Diez B. Roggisch" <de***@nospam.w eb.dewrites:

>The underscore is used as "discarded" identifier. So maybe

for _ in xrange(10):
...

The problem with the '_' name is that it is already well-known and
long-used existing convention for an entirely unrelated purpose:
in the 'gettext' i18n library, the '_' function to get the
locally-translated version of a text string.

Right, that's because I've used "__" where not all returning values
are interesing to me such as

a, b, __ = function_that_r eturns_three_va lues(x, y)

However, in loops, I prefer real names, even if the loop variable
isn't used outside.

Tschö,
Torsten.

--
Torsten Bronger, aquisgrana, europa vetus
Jabber ID: br*****@jabber. org
(See http://ime.webhop.org for further contact info.)

Torsten Bronger wrote:

>Hallöchen!

Ben Finney writes:

>"Diez B. Roggisch" <de***@nospam.w eb.dewrites:

>>The underscore is used as "discarded" identifier. So maybe

for _ in xrange(10):
...

The problem with the '_' name is that it is already well-known and
long-used existing convention for an entirely unrelated purpose:
in the 'gettext' i18n library, the '_' function to get the
locally-translated version of a text string.

Right, that's because I've used "__" where not all returning values
are interesing to me such as

a, b, __ = function_that_r eturns_three_va lues(x, y)

Variable name "dummy" serves the same purpose, such as:

a, b, dummy = function_that_r eturns_three_va lues(x, y)

According to http://linux.die.net/man/1/pylint it is also possible to use the
option

--dummy-variables-rgx=<regexp>

to further specify which variable not to report as unused. As far as I can
tell, it defaults to '_|dummy'.

..david

[Duncan Booth]

erik gartz <ee******@yahoo .comwrote:

Hi. I'd like to be able to write a loop such as:
for i in range(10):
pass
but without the i variable. The reason for this is I'm using pylint
and it complains about the unused variable i. I can achieve the above
with more lines of code like:
i = 0
while (i != 10):
i += 1
Is there a concise way to accomplish this without adding extra lines
of codes? Thanks in advance for your help.

Google for: pylint unused

It pointed me at:

Question:
I've a function / method which is a callback where I do not have any
control on received argument, and pylint is complaining about unused
arguments. What can I do to avoid those warnings ?

Answer:
prefix (ui) the callback's name by cb_, as in cb_onclick(...) . By doing
so arguments usage won't be checked. Another solution is to use one of
the name defined in the "dummy-variables" configuration variable for
unused argument ("_" and "dummy" by default).

http://www.iaeste.or.at/doc/python2..../html/FAQ.html

So it looks like you can use 'dummy' or add any other names you want to the
configuration.

[Torsten Bronger]

Hallöchen!

Da***********@s weco.no writes:

Torsten Bronger wrote:

>[...]

Right, that's because I've used "__" where not all returning
values are interesing to me such as

a, b, __ = function_that_r eturns_three_va lues(x, y)

Variable name "dummy" serves the same purpose, such as:

a, b, dummy = function_that_r eturns_three_va lues(x, y)

Granted, but my rationale is that "__" is less visible in the source
code, so there is more emphasis on the actually interesting
variables.

Tschö,
Torsten.

--
Torsten Bronger, aquisgrana, europa vetus
Jabber ID: br*****@jabber. org
(See http://ime.webhop.org for further contact info.)

Torsten Bronger writes:

>Da***********@ sweco.no writes:

>Torsten Bronger wrote:

>>[...]

Right, that's because I've used "__" where not all returning
values are interesing to me such as

a, b, __ = function_that_r eturns_three_va lues(x, y)

Variable name "dummy" serves the same purpose, such as:

a, b, dummy = function_that_r eturns_three_va lues(x, y)

Granted, but my rationale is that "__" is less visible in the source
code, so there is more emphasis on the actually interesting
variables.

I guess it's a matter of preference. Personally, I find "dummy" to be more
explicit, and hence more readable for those that that will read my code
later. YMMV.

Regards,
..david

[Mike Meyer]

On Thu, 10 Jan 2008 08:42:16 +0100 Hrvoje Niksic <hn*****@xemacs .orgwrote:

Mike Meyer <mw************ ***********@mir ed.orgwrites:

It sounds to me like your counter variable actually has meaning,

It depends how the code is written. In the example such as:

for meaningless_var iable in xrange(number_o f_attempts):
...

the loop variable really has no meaning. Rewriting this code only to
appease pylint is exactly that, it has nothing with making the code
more readable.

Except in this case, the variable *has* a meaning. You've just chosen
to obfuscate it.

you've hidden that meaning by giving it the meaningless name "i". If
you give it a meaningful name, then there's an obvious way to do it
(which you listed yourself):

while retries_left:

[...]

This loop contains more code and hence more opportunities for
introducing bugs. For example, if you use "continue" anywhere in the
loop, you will do one retry too much.

All correct - and I'm a big fan of minimizing code, as code you don't
write has no bugs in it. But you can still show the meaning of this
"meaningles s" variable:

for number_of_attem pts in xrange(maximum_ attempts):

Of course, the OP's request is a better solution: since he doesn't
actually need the variable, removing it completely means there's one
less variable, which is one less thing you can set to the wrong value.

<mike
--
Mike Meyer <mw*@mired.or g> http://www.mired.org/consulting.html
Independent Network/Unix/Perforce consultant, email for more information.