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Pythonic love

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  Pythonic love Fillmore <fillmore_remove@hotmail.com> - 2016-03-07 17:51 -0500
    Re: Pythonic love Rob Gaddi <rgaddi@highlandtechnology.invalid> - 2016-03-07 22:52 +0000
    Re: Pythonic love sohcahtoa82@gmail.com - 2016-03-07 15:03 -0800
      Re: Pythonic love Fillmore <fillmore_remove@hotmail.com> - 2016-03-07 18:12 -0500
    Re: Pythonic love Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-07 16:13 -0700
    Re: Pythonic love Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-07 23:19 +0000
    Re: Pythonic love jmp <jeanmichel@sequans.com> - 2016-03-08 14:25 +0100
    Re: Pythonic love justin walters <walters.justin01@gmail.com> - 2016-03-08 08:49 -0800
    Re: Pythonic love Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-08 16:55 +0000
    Re: Pythonic love jmp <jeanmichel@sequans.com> - 2016-03-08 18:00 +0100
    Re: Pythonic love justin walters <walters.justin01@gmail.com> - 2016-03-08 09:17 -0800
      Re: Pythonic love jstitch@invernalia.homelinux.net (Javier Novoa C.) - 2016-03-08 11:27 -0600
        Re: Pythonic love Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-03-08 21:10 -0500

#104262 — Pythonic love

learning Python from Perl here. Want to do things as Pythonicly as possible.

I am reading a TSV, but need to skip the first 5 lines. The following 
works, but wonder if there's a more pythonc way to do things. Thanks

ctr = 0
with open(prfile,mode="rt",encoding='utf-8') as pfile:
     for line in pfile:
         ctr += 1

         if ctr < 5:
             continue

         allVals = line.strip().split("\t")
         print(allVals)

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#104263

Fillmore wrote:

>
> learning Python from Perl here. Want to do things as Pythonicly as possible.
>
> I am reading a TSV, but need to skip the first 5 lines. The following 
> works, but wonder if there's a more pythonc way to do things. Thanks
>
> ctr = 0
> with open(prfile,mode="rt",encoding='utf-8') as pfile:
>      for line in pfile:
>          ctr += 1
>
>          if ctr < 5:
>              continue
>
>          allVals = line.strip().split("\t")
>          print(allVals)

for lineno, line in enumerate(pfile, start=1):

will save you maintaining your own counter.  But other than that, nah,
that's pretty much the approach you're looking for.

-- 
Rob Gaddi, Highland Technology -- www.highlandtechnology.com

Email address domain is currently out of order.  See above to fix.

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#104264

On Monday, March 7, 2016 at 2:51:50 PM UTC-8, Fillmore wrote:
> learning Python from Perl here. Want to do things as Pythonicly as possible.
> 
> I am reading a TSV, but need to skip the first 5 lines. The following 
> works, but wonder if there's a more pythonc way to do things. Thanks
> 
> ctr = 0
> with open(prfile,mode="rt",encoding='utf-8') as pfile:
>      for line in pfile:
>          ctr += 1
> 
>          if ctr < 5:
>              continue
> 
>          allVals = line.strip().split("\t")
>          print(allVals)

I'd read all the lines at once and then just slice the list.

with open(prfile, mode="rt", encoding="utf-8") as pfile:
    lines = pfile.readlines()[5:]
    for line in lines:
        allVals = line.strip().split("\t")
        print(allVals)

Obviously, this will only work well if your file is a reasonable size, as it will store the entire thing in memory at once.

On a side note, your "with open..." line uses inconsistent quoting.  You have "" on one string, but '' on another.

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#104266

On 3/7/2016 6:03 PM, sohcahtoa82@gmail.com wrote:

> On a side note, your "with open..." line uses inconsistent quoting.
 > You have "" on one string, but '' on another.

Thanks. I'll make sure I flog myself three times later tonight...

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#104267

On Mon, Mar 7, 2016 at 3:51 PM, Fillmore <fillmore_remove@hotmail.com> wrote:
>
> learning Python from Perl here. Want to do things as Pythonicly as possible.
>
> I am reading a TSV, but need to skip the first 5 lines. The following works,
> but wonder if there's a more pythonc way to do things. Thanks

I'd probably use itertools.islice.

from itertools import islice
for line in isiice(pfile, 5, None):
    allVals = line.strip().split("\t")
    print(allVals)

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#104269

On 07/03/2016 22:51, Fillmore wrote:
>
> learning Python from Perl here. Want to do things as Pythonicly as
> possible.
>
> I am reading a TSV, but need to skip the first 5 lines. The following
> works, but wonder if there's a more pythonc way to do things. Thanks
>
> ctr = 0
> with open(prfile,mode="rt",encoding='utf-8') as pfile:
>      for line in pfile:
>          ctr += 1
>
>          if ctr < 5:
>              continue
>
>          allVals = line.strip().split("\t")
>          print(allVals)

Something like this, completely untested.

with open(prfile,mode="rt",encoding='utf-8') as pfile:
     lineIter = iter(pfile)
     for _ in range(5):
         next(lineIter)
     for line in lineIter:
          allVals = line.strip().split("\t")
          print(allVals)

I'd also recommend that you use the csv module 
https://docs.python.org/3/library/csv.html which can also cope with tsv 
files, it's far more reliable than relying on a simple call to split().

-- 
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence

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#104334

On 03/07/2016 11:51 PM, Fillmore wrote:
>
> learning Python from Perl here. Want to do things as Pythonicly as
> possible.
>
> I am reading a TSV, but need to skip the first 5 lines. The following
> works, but wonder if there's a more pythonc way to do things. Thanks
>
> ctr = 0
> with open(prfile,mode="rt",encoding='utf-8') as pfile:
>      for line in pfile:
>          ctr += 1
>
>          if ctr < 5:
>              continue
>
>          allVals = line.strip().split("\t")
>          print(allVals)

what about a generator expression ? The (not so)new hype:

with open(prfile,mode="rt",encoding='utf-8') as pfile:
   for values in (l.strip().split("\t") for (i, l) in enumerate(pfile) 
if i >=5):
     print values

slightly dense, could be better with a lambda function

tovalues = lambda l: l.strip().split("\t")
with open(prfile,mode="rt",encoding='utf-8') as pfile:
   for values in (tovalues(l) for (i, l) in enumerate(pfile) if i >=5):
     print values


This should even work quite efficiently on big files, because I don't 
thing no more than one line is in memory at a given time.

jm

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#104344

Correct me if I'm wrong, but don't python generators usually use the yield
statement so they can be used in list comprehensions?
On Mar 8, 2016 5:27 AM, "jmp" <jeanmichel@sequans.com> wrote:

> On 03/07/2016 11:51 PM, Fillmore wrote:
>
>>
>> learning Python from Perl here. Want to do things as Pythonicly as
>> possible.
>>
>> I am reading a TSV, but need to skip the first 5 lines. The following
>> works, but wonder if there's a more pythonc way to do things. Thanks
>>
>> ctr = 0
>> with open(prfile,mode="rt",encoding='utf-8') as pfile:
>>      for line in pfile:
>>          ctr += 1
>>
>>          if ctr < 5:
>>              continue
>>
>>          allVals = line.strip().split("\t")
>>          print(allVals)
>>
>
> what about a generator expression ? The (not so)new hype:
>
> with open(prfile,mode="rt",encoding='utf-8') as pfile:
>   for values in (l.strip().split("\t") for (i, l) in enumerate(pfile) if i
> >=5):
>     print values
>
> slightly dense, could be better with a lambda function
>
> tovalues = lambda l: l.strip().split("\t")
> with open(prfile,mode="rt",encoding='utf-8') as pfile:
>   for values in (tovalues(l) for (i, l) in enumerate(pfile) if i >=5):
>     print values
>
>
> This should even work quite efficiently on big files, because I don't
> thing no more than one line is in memory at a given time.
>
> jm
>
>
>
>
> --
> https://mail.python.org/mailman/listinfo/python-list
>

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#104346

On 08/03/2016 16:49, justin walters wrote:
> Correct me if I'm wrong, but don't python generators usually use the yield
> statement so they can be used in list comprehensions?

Please don't top post on this list, thanks.

-- 
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence

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#104347

On 03/08/2016 05:49 PM, justin walters wrote:
> Correct me if I'm wrong, but don't python generators usually use the yield
> statement so they can be used in list comprehensions?

Hello,

Please don't top post.

Generator expressions are different from generator functions. They are 
both generators but use a different syntax.

generator function:

def func(iterable):
   for i in iterable: yield i


the generator expression version would be

(i for i in iterable)


Both have their use cases but everytime you can actually use an 
generator expression, it's probably the correct thing to do.

Cheers,

jm

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#104348

Sorry about the top posting. I'm new to mailing lists. I should just reply
to the python-list@python.org address then?

Also, thank you for the generator clarification.
On Mar 8, 2016 9:09 AM, "jmp" <jeanmichel@sequans.com> wrote:

> On 03/08/2016 05:49 PM, justin walters wrote:
>
>> Correct me if I'm wrong, but don't python generators usually use the yield
>> statement so they can be used in list comprehensions?
>>
>
> Hello,
>
> Please don't top post.
>
> Generator expressions are different from generator functions. They are
> both generators but use a different syntax.
>
> generator function:
>
> def func(iterable):
>   for i in iterable: yield i
>
>
> the generator expression version would be
>
> (i for i in iterable)
>
>
> Both have their use cases but everytime you can actually use an generator
> expression, it's probably the correct thing to do.
>
> Cheers,
>
> jm
>
> --
> https://mail.python.org/mailman/listinfo/python-list
>

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#104351

justin walters <walters.justin01@gmail.com> writes:

> Sorry about the top posting. I'm new to mailing lists. I should just reply
> to the python-list@python.org address then?
>
> Also, thank you for the generator clarification.
> On Mar 8, 2016 9:09 AM, "jmp" <jeanmichel@sequans.com> wrote:

^ that's top posting.... always reply inline or at the bottom

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#104379

On Tue, 08 Mar 2016 11:27:22 -0600, jstitch@invernalia.homelinux.net
(Javier Novoa C.) declaimed the following:

>justin walters <walters.justin01@gmail.com> writes:
>
>> Sorry about the top posting. I'm new to mailing lists. I should just reply
>> to the python-list@python.org address then?
>>
>> Also, thank you for the generator clarification.
>> On Mar 8, 2016 9:09 AM, "jmp" <jeanmichel@sequans.com> wrote:
>
>^ that's top posting.... always reply inline or at the bottom

	And, preferably, also trim anything that wasn't relevant (but this is
so short any trimming would lose context <G>)
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

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