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fprettify is an auto-formatter for modern Fortran code that imposes strict whitespace formatting, written in Python.

NOTE: I'm looking for help to maintain this repository, see #127.


  • Auto-indentation.
  • Line continuations are aligned with the previous opening delimiter (, [ or (/ or with an assignment operator = or =>. If none of the above is present, a default hanging indent is applied.
  • Consistent amount of whitespace around operators and delimiters.
  • Removal of extraneous whitespace and consecutive blank lines.
  • Change letter case (upper case / lower case conventions) of intrinsics
  • Tested for editor integration.
  • By default, fprettify causes whitespace changes only and thus preserves revision history.
  • fprettify can handle cpp and fypp preprocessor directives.


  • Works only for modern Fortran (Fortran 90 upwards).
  • Feature missing? Please create an issue.


  • Python 3 (Python 2.7 no longer supported)
  • ConfigArgParse: optional, enables use of config file


Compare examples/*before.f90 (original Fortran files) with examples/*after.f90 (reformatted Fortran files) to see what fprettify does. A quick demonstration:

program demo
integer :: endif,if,elseif
integer,DIMENSION(2) :: function
end program

⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩ fprettify ⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩

program demo
   integer :: endif, if, elseif
   integer, DIMENSION(2) :: function
   endif = 3; if = 2
   if (endif == 2) then
      endif = 5
      elseif = if + 4*(endif + &
   elseif (endif == 3) then
      function(if) = endif/elseif
      print *, endif
end program


The latest release can be installed using pip:

pip install --upgrade fprettify

Installation from source requires Python Setuptools:

pip install .

For local installation, use --user option.

If you use the Conda package manager, fprettify is available from the conda-forge channel:

conda install -c conda-forge fprettify

Command line tool

Autoformat file1, file2, ... inplace by

fprettify file1, file2, ...

The default indent is 3. If you prefer something else, use --indent n argument.

In order to apply fprettify recursively to an entire Fortran project instead of a single file, use the -r option.

For more options, read

fprettify -h

Editor integration

For editor integration, use

fprettify --silent

For instance, with Vim, use fprettify with gq by putting the following commands in your .vimrc:

autocmd Filetype fortran setlocal formatprg=fprettify\ --silent

Deactivation and manual formatting (experimental feature)

fprettify can be deactivated for selected lines: a single line followed by an inline comment starting with !& is not auto-formatted and consecutive lines that are enclosed between two comment lines !&< and !&> are not auto-formatted. This is useful for cases where manual alignment is preferred over auto-formatting. Furthermore, deactivation is necessary when non-standard Fortran syntax (such as advanced usage of preprocessor directives) prevents proper formatting. As an example, consider the following snippet of fprettify formatted code:

A = [-1, 10, 0, &
     0, 1000, 0, &
     0, -1, 1]

In order to manually align the columns, fprettify needs to be deactivated by

A = [-1,   10, 0, & !&
      0, 1000, 0, & !&
      0,   -1, 1]   !&

or, equivalently by

A = [-1,   10, 0, &
      0, 1000, 0, &
      0,   -1, 1]

Contributing / Testing

The testing mechanism allows you to easily test fprettify with any Fortran project of your choice. Simply clone or copy your entire project into fortran_tests/before and run python test. The directory fortran_tests/after contains the test output (reformatted Fortran files). If testing fails, please submit an issue!