Elementary string-formatting

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  • Odysseus
    #1

    Elementary string-formatting

    Hello, group: I've just begun some introductory tutorials in Python.
    Taking off from the "word play" exercise at

    <http://www.greenteapre ss.com/thinkpython/html/book010.html#to c96>

    I've written a mini-program to tabulate the number of characters in each
    word in a file. Once the data have been collected in a list, the output
    is produced by a while loop that steps through it by incrementing an
    index "i", saying

    print '%2u %6u %4.2f' % \
    (i, wordcounts[i], 100.0 * wordcounts[i] / wordcounts[0])

    My problem is with the last entry in each line, which isn't getting
    padded:

    1 0 0.00
    2 85 0.07
    3 908 0.80
    4 3686 3.24
    5 8258 7.26
    6 14374 12.63
    7 21727 19.09
    8 26447 23.24
    9 16658 14.64
    10 9199 8.08
    11 5296 4.65
    12 3166 2.78
    13 1960 1.72
    14 1023 0.90
    15 557 0.49
    16 261 0.23
    17 132 0.12
    18 48 0.04
    19 16 0.01
    20 5 0.00
    21 3 0.00

    I've tried varying the number before the decimal in the formatting
    string; "F", "g", and "G" conversions instead of "f"; and a couple of
    other permutations (including replacing the arithmetical expression in
    the tuple with a variable, defined on the previous line), but I can't
    seem to get the decimal points to line up. I'm sure I'm missing
    something obvious, but I'd appreciate a tip -- thanks in advance!

    FWIW I'm running

    Python 2.3.5 (#1, Oct 5 2005, 11:07:27)
    [GCC 3.3 20030304 (Apple Computer, Inc. build 1809)] on darwin

    from the Terminal on Mac OS X v10.4.11.

    P.S. Is there a preferable technique for forcing floating-point division
    of two integers to that used above, multiplying by "100.0" first? What
    about if I just wanted a ratio: is "float(n / m)" better than "1.0 * n /
    m"?

    --
    Odysseus
    Tags: None
    • Gary Herron
      #2
      Re: Elementary string-formatting

      Odysseus wrote:
      Hello, group: I've just begun some introductory tutorials in Python.
      Taking off from the "word play" exercise at
      >
      <http://www.greenteapre ss.com/thinkpython/html/book010.html#to c96>
      >
      I've written a mini-program to tabulate the number of characters in each
      word in a file. Once the data have been collected in a list, the output
      is produced by a while loop that steps through it by incrementing an
      index "i", saying
      >
      print '%2u %6u %4.2f' % \
      (i, wordcounts[i], 100.0 * wordcounts[i] / wordcounts[0])
      >
      Using 4.2 is the problem. The first digit (your 4) give the total
      number of characters to use for the number. Your numbers require at
      least 5 characters, two digits, one decimal point, and two more
      digits. So try 5.2, or 6.2 or 7.2 or higher if your numbers can grow
      into the hundreds or thousands or higher. If you want to try one of the
      floating point formats, then your first number must be large enough to
      account for digits (before and after) the decimal point, the 'E', and
      any digits in the exponent, as well as signs for both the number and the
      exponent.

      Gary Herron
      My problem is with the last entry in each line, which isn't getting
      padded:
      >
      1 0 0.00
      2 85 0.07
      3 908 0.80
      4 3686 3.24
      5 8258 7.26
      6 14374 12.63
      7 21727 19.09
      8 26447 23.24
      9 16658 14.64
      10 9199 8.08
      11 5296 4.65
      12 3166 2.78
      13 1960 1.72
      14 1023 0.90
      15 557 0.49
      16 261 0.23
      17 132 0.12
      18 48 0.04
      19 16 0.01
      20 5 0.00
      21 3 0.00
      >
      I've tried varying the number before the decimal in the formatting
      string; "F", "g", and "G" conversions instead of "f"; and a couple of
      other permutations (including replacing the arithmetical expression in
      the tuple with a variable, defined on the previous line), but I can't
      seem to get the decimal points to line up. I'm sure I'm missing
      something obvious, but I'd appreciate a tip -- thanks in advance!
      >
      FWIW I'm running
      >
      Python 2.3.5 (#1, Oct 5 2005, 11:07:27)
      [GCC 3.3 20030304 (Apple Computer, Inc. build 1809)] on darwin
      >
      from the Terminal on Mac OS X v10.4.11.
      >
      P.S. Is there a preferable technique for forcing floating-point division
      of two integers to that used above, multiplying by "100.0" first? What
      about if I just wanted a ratio: is "float(n / m)" better than "1.0 * n /
      m"?
      >
      >

        Comment

        • John Machin
          #3
          Re: Elementary string-formatting

          On Jan 13, 3:15 pm, Odysseus <odysseus1479.. .@yahoo-dot.cawrote:
          [snip]
          >
          P.S. Is there a preferable technique for forcing floating-point division
          of two integers to that used above, multiplying by "100.0" first? What
          about if I just wanted a ratio: is "float(n / m)" better than "1.0 * n /
          m"?
          Odysseus
          You obviously haven't tried float(n / m), or you wouldn't be asking.
          Go ahead and try it.

          "Preferable " depends on whether you want legibility or speed.

          Most legible and slowest first:
          1. float(n) / float(m)
          2. n / float(m)
          3. 1.0 * n / m
          # Rationale so far: function calls are slow
          4. If you have a lot of this to do, and you really care about the
          speed and m (the denominator) is constant throughout, do fm = float(m)
          once, and then in your loop do n / fm for each n -- and make sure you
          run properly constructed benchmarks ...

          Recommendation: go with (2) until you find you've got a program with
          a real speed problem (and then it probably won't be caused by this
          choice).

          HTH,
          John

            Comment

            • Roberto Bonvallet
              #4
              Re: Elementary string-formatting

              On Jan 12, 10:15 pm, Odysseus <odysseus1479.. .@yahoo-dot.cawrote:
              P.S. Is there a preferable technique for forcing floating-point division
              of two integers to that used above, multiplying by "100.0" first?
              Put this at the beginning of your program:

              from __future__ import division

              This forces all divisions to yield floating points values:
              >>1/3
              0
              >>from __future__ import division
              >>1/3
              0.3333333333333 3331
              >>>
              HTH,
              --
              Roberto Bonvallet

                Comment

                • Odysseus
                  #5
                  Re: Elementary string-formatting

                  In article
                  <a2185798-7fa1-4b8f-8ba0-1e21bcb22a78@d4 g2000prg.google groups.com>,
                  John Machin <sjmachin@lexic on.netwrote:

                  <snip>
                  >
                  You obviously haven't tried float(n / m), or you wouldn't be asking.
                  True, it was a very silly idea.
                  Most legible and slowest first:
                  1. float(n) / float(m)
                  2. n / float(m)
                  3. 1.0 * n / m
                  Recommendation: go with (2) until you find you've got a program with
                  a real speed problem (and then it probably won't be caused by this
                  choice).
                  I had actually used n / float(m) at one point; somehow the above struck
                  me as an improvement while I was writing the message. Thanks for the
                  reality check.

                  --
                  Odysseus

                    Comment

                    • Odysseus
                      #6
                      Re: Elementary string-formatting

                      In article
                      <e6f9c0c3-d248-46ae-af0f-fbb8ab279ab5@v4 6g2000hsv.googl egroups.com>,
                      Roberto Bonvallet <rbonvall@gmail .comwrote:
                      Put this at the beginning of your program:
                      >
                      from __future__ import division
                      >
                      This forces all divisions to yield floating points values:
                      Thanks for the tip. May I assume the div operator will still behave as
                      usual?

                      --
                      Odysseus

                        Comment

                        • John Machin
                          #7
                          Re: Elementary string-formatting

                          On Jan 13, 8:43 pm, Odysseus <odysseus1479.. .@yahoo-dot.cawrote:
                          In article
                          <e6f9c0c3-d248-46ae-af0f-fbb8ab279...@v4 6g2000hsv.googl egroups.com>,
                          Roberto Bonvallet <rbonv...@gmail .comwrote:
                          >
                          Put this at the beginning of your program:
                          >
                          from __future__ import division
                          >
                          This forces all divisions to yield floating points values:
                          >
                          Thanks for the tip. May I assume the div operator will still behave as
                          usual?
                          div operator? The integer division operator is //
                          >>from __future__ import division
                          >>1 / 3
                          0.3333333333333 3331
                          >>1 // 3
                          0
                          >>22 / 7
                          3.1428571428571 428
                          >>22 // 7
                          3
                          >>22 div 7
                          File "<stdin>", line 1
                          22 div 7
                          ^
                          SyntaxError: invalid syntax
                          >>>

                            Comment

                            • Odysseus
                              #8
                              Re: Elementary string-formatting

                              In article <mailman.561.12 00198783.896.py thon-list@python.org >,
                              Gary Herron <gherron@island training.comwro te:
                              Odysseus wrote:
                              <snip>

                              print '%2u %6u %4.2f' % \
                              (i, wordcounts[i], 100.0 * wordcounts[i] / wordcounts[0])
                              Using 4.2 is the problem. The first digit (your 4) give the total
                              number of characters to use for the number.
                              Thanks; I was thinking the numbers referred to digits before and after
                              the decimal. The largest figures have five characters in all, so they
                              were 'overflowing'.

                              --
                              Odysseus

                                Comment

                                • Matt Nordhoff
                                  #9
                                  Re: Elementary string-formatting

                                  Odysseus wrote:
                                  Hello, group: I've just begun some introductory tutorials in Python.
                                  Taking off from the "word play" exercise at
                                  >
                                  <http://www.greenteapre ss.com/thinkpython/html/book010.html#to c96>
                                  >
                                  I've written a mini-program to tabulate the number of characters in each
                                  word in a file. Once the data have been collected in a list, the output
                                  is produced by a while loop that steps through it by incrementing an
                                  index "i", saying
                                  >
                                  print '%2u %6u %4.2f' % \
                                  (i, wordcounts[i], 100.0 * wordcounts[i] / wordcounts[0])
                                  This isn't very important, but instead of keeping track of the index
                                  yourself, you can use enumerate():
                                  >>mylist = ['a', 'b', 'c']
                                  >>for i, item in enumerate(mylis t):
                                  .... print i, item
                                  ....
                                  0 a
                                  1 b
                                  2 c
                                  >>>
                                  Err, it doesn't look like you can make it start at 1 though.

                                  <snip>
                                  --

                                    Comment

                                    • Odysseus
                                      #10
                                      Re: Elementary string-formatting

                                      In article
                                      <7d17fa05-67c5-4acb-91b6-c53fdf70ae27@q7 7g2000hsh.googl egroups.com>,
                                      John Machin <sjmachin@lexic on.netwrote:

                                      <snip>
                                      >
                                      div operator? The integer division operator is //
                                      Yes, sorry, that's what I meant.

                                      --
                                      Odysseus

                                        Comment

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