sable-fortran 0.1.5

An uncompromising Fortran formatter, inspired by Black

An uncompromising Fortran formatter, inspired by Black.

"So it goes." — Kurt Vonnegut, Slaughterhouse-Five

Sable enforces one consistent style for modern free-form Fortran, so you can focus on code instead of formatting.

Installation

pip install sable-fortran

Usage

# Format a file or directory in place
sable my_module.f90
sable src/

# Check formatting without changing files (exit 1 if changes are needed)
sable --check src/

# Preview changes as a unified diff
sable --diff src/

# Check + diff together (non-zero if any file would change)
sable --check --diff src/

# Migration mode: only low-risk whitespace/layout changes
sable --safe src/

# Format piped input (Sable reads stdin when no files are passed)
cat code.f90 | sable

# Optional: label stdin input in diagnostics
cat code.f90 | sable --stdin-filename my_module.f90

Directory scans include .f90, .F90, .f95, .F95, .f03, .F03, .f08, and .F08 files.

What Sable changes

• Normalizes keyword/operator style (INTEGER -> integer, .EQ. -> ==, endif -> end if by default).
• Applies consistent spacing and indentation.
• Wraps long lines deterministically (including one-argument-per-line layouts).
• Canonicalizes declarations (::, stable attribute order).
• Preserves directives and formatting-off regions (! sable: off / on).
• Guarantees idempotent output with exactly one trailing newline.

! Before
IF(A .EQ. B)THEN
CALL compute(alpha_input,beta_input,gamma_input,result_output)
ENDIF

! After
if (A == B) then
   call compute(    &
      alpha_input,  &
      beta_input,   &
      gamma_input,  &
      result_output &
   )
end if

Formatting rules (quick reference)

Old	New
.EQ.	==
.NE.	/=
.LT.	<
.LE.	<=
.GT.	>
.GE.	>=

• Keywords are lower-case by default (--keyword-case upper to change).
• Names are preserved exactly as written.
• End keywords use spaced forms by default (end if, end do; configurable).
• .AND., .OR., .NOT., .EQV., .NEQV. are preserved.
• One space around most binary operators; no spaces around % or **.
• No spaces inside parens/brackets.
• Two spaces before inline comments (x = 1 ! note).
• Default indent is 3 spaces (--indent-width to change).
• Long lines wrap with & using deterministic split rules (--line-length).
• Multi-statement lines split into one statement per line.

Configuration

Sable intentionally exposes few options:

Flag	Default	Description
--line-length, -l	100	Max line length
--indent-width, -i	3	Spaces per indent level
--keyword-case	lower	lower or upper
--end-keyword-form	spaced	spaced or compact
--no-normalize-operators	off	Keep old-style relational operators
--safe	off	Migration mode; skip non-safe syntax/canonicalization rewrites
--quiet	off	Suppress non-error status output

Name

Sable is heraldic for black — a nod to Black, the Python formatter that inspired this project.

License

MIT