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Re: How can I remove the first line of a multi-line string? (SOLVED)

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  Re: How can I remove the first line of a multi-line string? (SOLVED) Anthony Papillion <papillion@gmail.com> - 2013-09-02 11:24 -0500
    Re: How can I remove the first line of a multi-line string? (SOLVED) Roy Smith <roy@panix.com> - 2013-09-02 13:07 -0400
      Re: How can I remove the first line of a multi-line string? (SOLVED) Fábio Santos <fabiosantosart@gmail.com> - 2013-09-11 13:08 +0100
        Re: How can I remove the first line of a multi-line string? (SOLVED) Roy Smith <roy@panix.com> - 2013-09-11 09:03 -0400
      Re: How can I remove the first line of a multi-line string? (SOLVED) Terry Reedy <tjreedy@udel.edu> - 2013-09-11 08:42 -0400

#53502 — Re: How can I remove the first line of a multi-line string? (SOLVED)

On 09/02/2013 11:12 AM, Chris “Kwpolska” Warrick wrote:
> On Mon, Sep 2, 2013 at 6:06 PM, Anthony Papillion <papillion@gmail.com> wrote:
>> Hello Everyone,
>>
>> I have a multi-line string and I need to remove the very first line from
>> it. How can I do that? I looked at StringIO but I can't seem to figure
>> out how to properly use it to remove the first line. Basically, I want
>> to toss the first line but keep everything else.  Can anyone put me on
>> the right path? I know it is probably easy but I'm still learning Python
>> and don't have all the string functions down yet.
>>
>> Thanks,
>> Anthony
>> --
>> http://mail.python.org/mailman/listinfo/python-list
> 
> Use split() and join() methods of strings, along with slicing.  Like this:
> 
>     fullstring = """foo
>     bar
>     baz"""
> 
>     sansfirstline = '\n'.join(fullstring.split('\n')[1:])
> 
> The last line does this:
> 1. fullstring.split('\n') turns it into a list of ['foo', 'bar', 'baz']
> 2. the [1:] slice removes the first element, making it ['bar', 'baz']
> 3. Finally, '\n'.join() turns the list into a string separated by
> newlines ("""bar
> baz""")

This, of course, worked like a charm. I really need to study the string
methods. In the work I'm doing they are going to come in very handy.
Thank you, Chris!

Anthony

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#53505

In article <mailman.500.1378139057.19984.python-list@python.org>,
 Anthony Papillion <papillion@gmail.com> wrote:

> On 09/02/2013 11:12 AM, Chris “Kwpolska” Warrick wrote:
> > On Mon, Sep 2, 2013 at 6:06 PM, Anthony Papillion <papillion@gmail.com> 
> > wrote:
> >> Hello Everyone,
> >>
> >> I have a multi-line string and I need to remove the very first line from
> >> it. How can I do that? I looked at StringIO but I can't seem to figure
> >> out how to properly use it to remove the first line. Basically, I want
> >> to toss the first line but keep everything else.  Can anyone put me on
> >> the right path? I know it is probably easy but I'm still learning Python
> >> and don't have all the string functions down yet.
> >>
> >> Thanks,
> >> Anthony
> >> --
> >> http://mail.python.org/mailman/listinfo/python-list
> > 
> > Use split() and join() methods of strings, along with slicing.  Like this:
> > 
> >     fullstring = """foo
> >     bar
> >     baz"""
> > 
> >     sansfirstline = '\n'.join(fullstring.split('\n')[1:])
> > 
> > The last line does this:
> > 1. fullstring.split('\n') turns it into a list of ['foo', 'bar', 'baz']
> > 2. the [1:] slice removes the first element, making it ['bar', 'baz']
> > 3. Finally, '\n'.join() turns the list into a string separated by
> > newlines ("""bar
> > baz""")
> 
> This, of course, worked like a charm. I really need to study the string
> methods. In the work I'm doing they are going to come in very handy.
> Thank you, Chris!

Let me toss out a couple of other possibilities.  Not necessarily 
better, but if you're learning about strings, you might as well learn 
some other ways to do it:


s = """foo                                                                                          
     
bar                                                                                            
     
baz"""

print "using index..."
i = s.index('\n')
print s[i+1:]

print "using regex..."
import re
print re.sub(r'^[^\n]*\n', '', s)


I'll admit, the split/slice/join solution is probably the easiest to 
implement (and to understand when you're reading the code).  But, it 
copies all the data twice; once when split() runs, and again when join() 
runs.  Both the index and regex solutions should only do a single copy.  
For huge strings, this might matter.  For a three-liner as in your 
example, it doesn't make any difference.

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#53955

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On 2 Sep 2013 18:13, "Roy Smith" <roy@panix.com> wrote:
>
> In article <mailman.500.1378139057.19984.python-list@python.org>,
>  Anthony Papillion <papillion@gmail.com> wrote:
>
> > On 09/02/2013 11:12 AM, Chris “Kwpolska” Warrick wrote:
> > > On Mon, Sep 2, 2013 at 6:06 PM, Anthony Papillion <papillion@gmail.com
>
> > > wrote:
> > >> Hello Everyone,
> > >>
> > >> I have a multi-line string and I need to remove the very first line
from
> > >> it. How can I do that? I looked at StringIO but I can't seem to
figure
> > >> out how to properly use it to remove the first line. Basically, I
want
> > >> to toss the first line but keep everything else.  Can anyone put me
on
> > >> the right path? I know it is probably easy but I'm still learning
Python
> > >> and don't have all the string functions down yet.
> > >>
> > >> Thanks,
> > >> Anthony
> > >> --
> > >> http://mail.python.org/mailman/listinfo/python-list
> > >
> > > Use split() and join() methods of strings, along with slicing.  Like
this:
> > >
> > >     fullstring = """foo
> > >     bar
> > >     baz"""
> > >
> > >     sansfirstline = '\n'.join(fullstring.split('\n')[1:])
> > >
> > > The last line does this:
> > > 1. fullstring.split('\n') turns it into a list of ['foo', 'bar',
'baz']
> > > 2. the [1:] slice removes the first element, making it ['bar', 'baz']
> > > 3. Finally, '\n'.join() turns the list into a string separated by
> > > newlines ("""bar
> > > baz""")
> >
> > This, of course, worked like a charm. I really need to study the string
> > methods. In the work I'm doing they are going to come in very handy.
> > Thank you, Chris!
>
> Let me toss out a couple of other possibilities.  Not necessarily
> better, but if you're learning about strings, you might as well learn
> some other ways to do it:
>
>
> s = """foo
>
> bar
>
> baz"""
>
> print "using index..."
> i = s.index('\n')
> print s[i+1:]
>
> print "using regex..."
> import re
> print re.sub(r'^[^\n]*\n', '', s)
>
>
> I'll admit, the split/slice/join solution is probably the easiest to
> implement (and to understand when you're reading the code).  But, it
> copies all the data twice; once when split() runs, and again when join()
> runs.  Both the index and regex solutions should only do a single copy.
> For huge strings, this might matter.  For a three-liner as in your
> example, it doesn't make any difference.
>

Is there not a limit argument to str.split? This should be trivial.

first, rest = multiline_str.split('\n', 1)

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#53960

In article <mailman.244.1378901307.5461.python-list@python.org>,
 Fábio Santos <fabiosantosart@gmail.com> wrote:

One suggested solution:
> > > >     sansfirstline = '\n'.join(fullstring.split('\n')[1:])

To which I suggested a couple of alternatives:
> > i = s.index('\n')
> > print s[i+1:]
> > [...]
> > print re.sub(r'^[^\n]*\n', '', s)


> > I'll admit, the split/slice/join solution is probably the easiest to
> > implement (and to understand when you're reading the code).  But, it
> > copies all the data twice; once when split() runs, and again when join()
> > runs.  Both the index and regex solutions should only do a single copy.
> > For huge strings, this might matter.  For a three-liner as in your
> > example, it doesn't make any difference.
> >
> 
> Is there not a limit argument to str.split? This should be trivial.
> 
> first, rest = multiline_str.split('\n', 1)

This certainly prevents the extra splitting and re-compositing of the 
additional lines.

One thing to watch out for is that split(s, 1) does *at most* 1 split.  
If the original string didn't have any newlines, you would end up with a 
single-item list and the unpack would fail.  You can get around that 
with:

rest = multiline_str.split('\n', 1)[-1]

but that's kind of cryptic.

Looking back at my solutions suggested above, s.index() fails in the 
same situation (throws ValueError).  The regex solution works fine, once 
again proving that 1970's technology is still superior to all this 
newfangled stuff.

A coworker recently introduced me to what is apparently a classic essay 
(http://www.team.net/mjb/hawg.html).  If Unix is the Hole Hawg of 
operating systems, then regexes are the Hole Hawg of string processing 
tools.  Those of us who grew up around them, appreciate their power and 
have learned how to use them without chopping off any fingers.  And we 
look on with a mix of amusement and pity at the current crop of 
programmers who play with index(), split(), startswith(), rpartition(), 
etc and think they're using real tools :-)

For the record, I have never used a Hole Hawg.  I do, however, own a 
Milwaukee 1/2" drill.  Which also comes with the screw-in handle for 
two-handed operation.  I've had that get away from me a couple of times, 
so I figure it's about my limit.  Torque is a wonderful thing until the 
thing you're drilling into weighs more than you do.

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#53956

On 9/11/2013 8:08 AM, Fábio Santos wrote:

> Is there not a limit argument to str.split? This should be trivial.

Yes, I posted an example using it the first day.

I also showed how to use iter and next with files and avoid copying.

> first, rest = multiline_str.split('\n', 1)

This does not work right is there is no '\n'

Then someone pointed out
first, dummy, rest = partition('\n')
which does work with no '\n'

-- 
Terry Jan Reedy

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