How do I tell the difference between the end of a text file, and an empty line in a text file?

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  • walterbyrd
    #1

    How do I tell the difference between the end of a text file, and an empty line in a text file?

    Python's lack of an EOF character is giving me a hard time.

    I've tried:

    -----
    s = f.readline()
    while s:
    ..
    ..
    s = f.readline()
    --------

    and

    -------
    s = f.readline()
    while s != ''
    ..
    ..
    s = f.readline()
    -------


    In both cases, the loop ends as soon it encounters an empty line in
    the file, i.e.


    xxxxxxxxxx
    xxxxxxxxxxx
    xxxxxxx
    < - - - loop end here
    xxxxxxxxxxxxxx
    xxxxxxxxxx
    x
    < ---- loop should end here

    Tags: None
    • James Stroud
      #2
      Re: How do I tell the difference between the end of a text file,and an empty line in a text file?

      walterbyrd wrote:
      Python's lack of an EOF character is giving me a hard time.
      >
      I've tried:
      >
      [ stuff ]

      for s in f:
      do_whatever_wit h_s(s)


      James

        Comment

        • Grant Edwards
          #3
          Re: How do I tell the difference between the end of a text file, and an empty line in a text file?

          On 2007-05-16, walterbyrd <walterbyrd@ina me.comwrote:
          Python's lack of an EOF character is giving me a hard time.
          No it isn't.
          s = f.readline()
          while s:
          .
          .
          s = f.readline()

          s = f.readline()
          while s != ''
          .
          .
          s = f.readline()

          Neither one of your examples is legal Python. Please post real
          code.
          In both cases, the loop ends as soon it encounters an empty line in
          the file, i.e.
          No, it doesn't. Not if you've done something reasonable like
          this:

          f = open('testdata' ,'r')
          while True:
          s = f.readline()
          if not s: break
          print repr(s)

          or this:

          f = open('testdata' ,'r')
          s = f.readline()
          while s:
          print repr(s)
          s = f.readline()

          Please post real, runnable code. You've done something wrong
          and we've no way to guess what it was if you won't show us your
          code.

          --
          Grant Edwards grante Yow! Is something VIOLENT
          at going to happen to a
          visi.com GARBAGE CAN?

            Comment

            • James Stroud
              #4
              Re: How do I tell the difference between the end of a text file,and an empty line in a text file?

              Grant Edwards wrote:
              On 2007-05-16, walterbyrd <walterbyrd@ina me.comwrote:
              >
              >
              >>Python's lack of an EOF character is giving me a hard time.
              >
              >
              No it isn't.
              >
              >
              >>s = f.readline()
              >>while s:
              >>.
              >>.
              >>s = f.readline()
              >
              >
              >
              >
              >>s = f.readline()
              >>while s != ''
              >>.
              >>.
              >>s = f.readline()
              >
              >
              >
              Neither one of your examples is legal Python. Please post real
              code.
              >
              >
              >>In both cases, the loop ends as soon it encounters an empty line in
              >>the file, i.e.
              >
              >
              No, it doesn't. Not if you've done something reasonable like
              this:
              >
              f = open('testdata' ,'r')
              while True:
              s = f.readline()
              if not s: break
              print repr(s)
              >
              or this:
              >
              f = open('testdata' ,'r')
              s = f.readline()
              while s:
              print repr(s)
              s = f.readline()
              >
              Please post real, runnable code. You've done something wrong
              and we've no way to guess what it was if you won't show us your
              code.
              >
              I'm guessing it was runnable when he pasted it into google groups.

              James

                Comment

                • Steven Bethard
                  #5
                  Re: How do I tell the difference between the end of a text file,and an empty line in a text file?

                  walterbyrd wrote:
                  Python's lack of an EOF character is giving me a hard time.
                  >
                  I've tried:
                  >
                  -----
                  s = f.readline()
                  while s:
                  .
                  .
                  s = f.readline()
                  --------
                  >
                  and
                  >
                  -------
                  s = f.readline()
                  while s != ''
                  .
                  .
                  s = f.readline()
                  -------
                  >
                  >
                  In both cases, the loop ends as soon it encounters an empty line in
                  the file, i.e.
                  That's just not true. Did you try that code?
                  >>open('temp.tx t', 'w').write('''\
                  .... xxxxxxxxxx
                  .... xxxxxxxxxxx
                  .... xxxxxxx
                  ....
                  .... xxxxxxxxxxxxxx
                  .... xxxxxxxxxx
                  .... x
                  .... ''')
                  >>while s:
                  .... print s,
                  .... s = f.readline()
                  ....
                  >>f = open('temp.txt' )
                  >>s = f.readline()
                  >>while s:
                  .... print s,
                  .... s = f.readline()
                  ....
                  xxxxxxxxxx
                  xxxxxxxxxxx
                  xxxxxxx

                  xxxxxxxxxxxxxx
                  xxxxxxxxxx
                  x

                  The file.readline() method returns '\n' for empty lines and '' for
                  end-of-file.

                  STeVe

                    Comment

                    • Dan Bishop
                      #6
                      Re: How do I tell the difference between the end of a text file, and an empty line in a text file?

                      On May 16, 4:47 pm, walterbyrd <walterb...@ina me.comwrote:
                      Python's lack of an EOF character is giving me a hard time.
                      >
                      I've tried:
                      >
                      -----
                      s = f.readline()
                      while s:
                      .
                      .
                      s = f.readline()
                      --------
                      >
                      and
                      >
                      -------
                      s = f.readline()
                      while s != ''
                      .
                      .
                      s = f.readline()
                      -------
                      >
                      In both cases, the loop ends as soon it encounters an empty line in
                      the file, i.e.
                      >
                      xxxxxxxxxx
                      xxxxxxxxxxx
                      xxxxxxx
                      < - - - loop end here
                      xxxxxxxxxxxxxx
                      xxxxxxxxxx
                      x
                      < ---- loop should end here
                      Use a "for s in f" loop instead.

                        Comment

                        • casevh@gmail.com
                          #7
                          Re: How do I tell the difference between the end of a text file, and an empty line in a text file?

                          On May 16, 2:47 pm, walterbyrd <walterb...@ina me.comwrote:
                          Python's lack of an EOF character is giving me a hard time.
                          >
                          I've tried:
                          >
                          -----
                          s = f.readline()
                          while s:
                          .
                          .
                          s = f.readline()
                          --------
                          >
                          and
                          >
                          -------
                          s = f.readline()
                          while s != ''
                          .
                          .
                          s = f.readline()
                          -------
                          >
                          In both cases, the loop ends as soon it encounters an empty line in
                          the file, i.e.
                          >
                          xxxxxxxxxx
                          xxxxxxxxxxx
                          xxxxxxx
                          < - - - loop end here
                          xxxxxxxxxxxxxx
                          xxxxxxxxxx
                          x
                          < ---- loop should end here
                          Assuming f is initialized as in your example, try

                          ---------
                          for s in f:
                          print s
                          ---------

                          casevh

                            Comment

                            • Asun Friere
                              #8
                              Re: How do I tell the difference between the end of a text file, and an empty line in a text file?

                              On May 17, 7:47 am, walterbyrd <walterb...@ina me.comwrote:
                              Python's lack of an EOF character is giving me a hard time.
                              The difference is simply that an empty line contains a '\n' while EOF
                              does not. If you strip() your line before testing you will have
                              trouble. But the minimal cases you post (properly indented and with
                              the missing ':' in place), should work (they just won't produce any
                              output). Repairing the first , I'm using dots (aka stops, periods) for
                              spaces here to stop the code getting munged :

                              line = fobj.readline()
                              while line :
                              .....print line.strip()
                              .....line = fobj.realine()

                              This does work look at this output (and note the empty lines):
                              line with stuff
                              line with more stuff

                              line after the empty line and before another

                              last line

                              In python it is more ideomatic to write this general kind of loop with
                              a break statement, thus:

                              while True :
                              .....line = fobj.readline()
                              .....if not line : break
                              .....print line.strip()

                              However since file has for a long time been an iterable the easiest
                              and most readible way to write it is this:

                              for line in fobj :
                              .....print line.strip()

                              Asun

                                Comment

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