gpp (conditional compilation)

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  • maxwell@ldc.upenn.edu
    #1

    gpp (conditional compilation)

    I'm trying to use the gpp utility (Gnu points to http://en.nothingisreal.com/wiki/GPP)
    to do conditional compilation in Python, and I'm running into a
    problem: the same '#' character introduces Python comments and is used
    by default to introduce #ifdef etc. lines.

    Here's an example of what I'm trying to do:

    #ifdef DEBUG
    stderr.write("v ariable is...") #details of msg omitted
    #endif

    I'm using the following args to gpp:
    +s \" \" \" +s \' \' \' +c \\\# \\n -n
    The result is that the #ifdef and #endif lines get treated as
    comments, rather than instructions to gpp to keep or omit the lines in
    between.

    I tried just omitting the +c arg, but then I get msgs at the end of
    each file saying
    Input ended while scanning a comment/string
    apparently because I use apostrophes inside comments, and gpp thinks
    those are unterminated strings.

    I can think of some work-arounds, like "don't use apostrophes inside
    comments", or "don't use single-quoted strings (or define them for
    gpp)" or "use a different char for the first char of a gpp macro".
    But I'd rather not...

    Does anyone have a set of gpp args that plays well with Python? (Or
    makefiles, where I presume the same problem comes up.)

    Mike Maxwell
    CASL/ U MD

    Tags: None
    • Duncan Booth
      #2
      Re: gpp (conditional compilation)

      "maxwell@ldc.up enn.edu" <maxwell@umiacs .umd.eduwrote:
      I'm trying to use the gpp utility (Gnu points to
      http://en.nothingisreal.com/wiki/GPP) to do conditional compilation in
      Python, and I'm running into a problem: the same '#' character
      introduces Python comments and is used by default to introduce #ifdef
      etc. lines.
      >
      Here's an example of what I'm trying to do:
      >
      #ifdef DEBUG
      stderr.write("v ariable is...") #details of msg omitted
      #endif
      >
      Why do you want conditional compilation. Is there anything wrong with:

      if __debug__:
      stderr.write("v ariable is...") #details of msg omitted

      If you run Python with the -O command line option the code protected by the
      if statement will be optimised out.

      For most other purposes where you might use conditional compilation just
      adding 'if' statements to execute at runtime (or try/except) will do the
      same purpose:

      if sys.platform==' win32':
      def foo():
      ... something ...
      else:
      def foo():
      .... something different ...

        Comment

        • John Nagle
          #3
          Re: gpp (conditional compilation)

          maxwell@ldc.upe nn.edu wrote:
          I'm trying to use the gpp utility (Gnu points to http://en.nothingisreal.com/wiki/GPP)
          to do conditional compilation in Python, and I'm running into a
          problem: the same '#' character introduces Python comments and is used
          by default to introduce #ifdef etc. lines.
          Just use an "if" statement. The Python interpreter is so slow
          it won't matter.

          John Nagle

            Comment

            • dustin@v.igoro.us
              #4
              Re: gpp (conditional compilation)

              On Wed, May 02, 2007 at 10:37:40AM -0700, maxwell@ldc.upe nn.edu wrote:
              I'm trying to use the gpp utility (Gnu points to http://en.nothingisreal.com/wiki/GPP)
              to do conditional compilation in Python, and I'm running into a
              problem: the same '#' character introduces Python comments and is used
              by default to introduce #ifdef etc. lines.
              The hacks you'll need to wrap gpp in to get it to work will make your
              head spin.

              I'm not sure what brought you to gpp, but if you're looking for a basic
              macro-processing language suitable for the kinds of tasks the C
              preprocessor performs, I would recommend M4. GNU has an implementation
              of the language, and it's actually quite widely used as the basis for
              the GNU autotools suite. It is incredibly flexible (enough so that its
              learning curve is a bit steep, but not too bad), but that flexibility
              enables it to work with just about any underlying language.

              Dustin

                Comment

                • maxwell@ldc.upenn.edu
                  #5
                  Re: gpp (conditional compilation)

                  (replying to myself because I got four good replies)

                  Wow! That was fast! OK, I'll try out these ideas, and many thanks!

                  Mike Maxwell

                    Comment

                    • Cameron Laird
                      #6
                      Re: gpp (conditional compilation)

                      In article <Xns9924BED31AD 3Aduncanbooth@1 27.0.0.1>,
                      Duncan Booth <duncan.booth@s uttoncourtenay. org.ukwrote:
                      >"maxwell@ldc.u penn.edu" <maxwell@umiacs .umd.eduwrote:
                      >
                      >I'm trying to use the gpp utility (Gnu points to
                      >http://en.nothingisreal.com/wiki/GPP) to do conditional compilation in
                      >Python, and I'm running into a problem: the same '#' character
                      >introduces Python comments and is used by default to introduce #ifdef
                      >etc. lines.
                      >>
                      >Here's an example of what I'm trying to do:
                      >>
                      >#ifdef DEBUG
                      > stderr.write("v ariable is...") #details of msg omitted
                      >#endif
                      >>
                      >
                      >Why do you want conditional compilation. Is there anything wrong with:
                      >
                      if __debug__:
                      stderr.write("v ariable is...") #details of msg omitted
                      >
                      >If you run Python with the -O command line option the code protected by the
                      >if statement will be optimised out.
                      >
                      >For most other purposes where you might use conditional compilation just
                      >adding 'if' statements to execute at runtime (or try/except) will do the
                      >same purpose:
                      >
                      >if sys.platform==' win32':
                      def foo():
                      ... something ...
                      >else:
                      def foo():
                      .... something different ...
                      I want to reinforce this. Yes, it is possible to pre-process Python
                      source, it's even been done before, and I'm sympathetic to the
                      suggestion that m4's more appropriate than gpp.

                      However, Duncan and others who've followed up are right: you can
                      live without this stuff. In fact, those who think they need condi-
                      tional compilation with Python are, with very few exceptions, simply
                      mistaken. The urge to transform Python source this way almost always
                      is a symptom of unfamiliarity with Python potential and good style.

                      It's not just that Python can do without conditional compilation;
                      Python offers *better* means to achieve the same goals.

                        Comment

                        • Gabriel Genellina
                          #7
                          Re: gpp (conditional compilation)

                          En Wed, 02 May 2007 14:37:40 -0300, maxwell@ldc.upe nn.edu
                          <maxwell@umiacs .umd.eduescribi รณ:
                          I'm trying to use the gpp utility (Gnu points to
                          http://en.nothingisreal.com/wiki/GPP)
                          to do conditional compilation in Python, and I'm running into a
                          problem: the same '#' character introduces Python comments and is used
                          by default to introduce #ifdef etc. lines.
                          >
                          Here's an example of what I'm trying to do:
                          >
                          #ifdef DEBUG
                          stderr.write("v ariable is...") #details of msg omitted
                          #endif
                          In addition to all previous comments, I just want to menction the
                          existence of Tools/Scripts/ifdef.py, included in every Python install; it
                          can process #if #ifdef #else etc.

                          --
                          Gabriel Genellina

                            Comment

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