Fypp — Python powered Fortran metaprogramming

Fypp is a Python powered preprocessor. It can be used for any programming languages but its primary aim is to offer a Fortran preprocessor, which helps to extend Fortran with condititional compiling and template metaprogramming capabilities. Instead of introducing its own expression syntax, it uses Python expressions in its preprocessor directives, offering the consistency and versatility of Python when formulating metaprogramming tasks. It puts strong emphasis on robustness and on neat integration into developing toolchains.

The project is hosted on bitbucket.

Detailed DOCUMENTATION is available on readthedocs.org.

Fypp is released under the BSD 2-clause license.

Main features

• Definition and evaluation of preprocessor variables:

  #:if DEBUG > 0
    print *, "Some debug information"
  #:endif
  
  #:setvar LOGLEVEL 2
  

• Macro defintions and macro calls (apart of minor syntax differences similar to scoped intelligent Fortran macros, which probably will once become part of the Fortran standard):

  #:def assertTrue(cond)
  #:if DEBUG > 0
  if (.not. ${cond}$) then
    print *, "Assert failed in file ${_FILE_}$, line ${_LINE_}$"
    error stop
  end if
  #:endif
  #:enddef
  
  ! Invoked via direct call (needs no quotation)
  @:assertTrue size(myArray) > 0
  
  ! Invoked as Python expression (needs quotation)
  $:assertTrue('size(myArray) > 0')
  

• Conditional output:

  program test
  #:if defined('WITH_MPI')
    use mpi
  #:elif defined('WITH_OPENMP')
    use openmp
  #:else
    use serial
  #:endif
  

• Iterated output (e.g. for generating Fortran templates):

  interface myfunc
  #:for dtype in [ 'real', 'dreal', 'complex', 'dcomplex' ]
    module procedure myfunc_${dtype}$
  #:endfor
  end interface myfunc
  

• Inline directives:

  logical, parameter :: hasMpi = #{if defined('MPI')}#.true.#{else}#.false.#{endif}#
  

• Insertion of arbitrary Python expressions:

  character(*), parameter :: comp_date = "${time.strftime('%Y-%m-%d')}$"
  

• Inclusion of files during preprocessing:

  #:include "macrodefs.fypp"
  

• Using Fortran-style continutation lines in preprocessor directives:

  #:if var1 > var2 &
      & or var2 > var4
    print *, "Doing something here"
  #:endif
  

• Passing multiline string arguments to macros:

  #:def debug_code(code)
    #:if DEBUG > 0
      $:code
    #:endif
  #:enddef
  
  #:call debug_code
    if (size(array) > 100) then
      print *, "DEBUG: spuriously large array"
    end if
  #:endcall
  

• Preprocessor comments:

  #! This will not show up in the output
  #! Also the newline characters at the end of the lines will be suppressed
  

• Suppressing the preprocessor output in selected regions:

  #! Definitions are read, but no output (e.g. newlines) will be produced
  #:mute
  #:include "macrodefs.fypp"
  #:endmute
  

Installing

Fypp needs a Python interpreter of version 2.7, 3.2 or above.

Automatic install

Use Pythons command line installer pip in order to download the stable release from the Fypp page on PyPI and install it on your system:

pip install fypp

This installs both, the command line tool fypp and the Python module fypp.py. Latter you can import if you want to access the functionality of Fypp directly from within your Python scripts.

Manual install

For a manual install, you can download the source code from the Fypp project website

git clone https://aradi@bitbucket.org/aradi/fypp.git

The project follows Vincent Driessens git workflow, so in order to obtain

• the latest stable version, check out the master branch:

  cd fypp
  git co master
  

• the latest development snapshot, check out the develop branch:

  cd fypp
  git co develop
  

The command line tool is a single stand-alone script. You can run it directly from the source folder

FYPP_SOURCE_FOLDER/bin/fypp

or after copying it from the bin folder to any location listed in your PATH environment variable, by just issuing

fypp

The python module fypp.py can be found in FYP_SOURCE_FOLDER/src.

Running

The Fypp command line tool reads a file, preprocesses it and writes it to another file, so you would typically invoke it like:

fypp source.F90 source.f90

which would process source.F90 and write the result to source.f90. If input and output files are not specified, information is read from stdin and written to stdout.

The behavior of Fypp can be influenced with various command line options. A summary of all command line options can be obtained by:

fypp -h