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# F2PY and Windows Intel Fortran

As of NumPy 1.23, only the classic Intel compilers (`ifort`) are supported.

Note

The licensing restrictions for beta software have been relaxed during the transition to the LLVM backed `ifx/icc` family of compilers. However this document does not endorse the usage of Intel in downstream projects due to the issues pertaining to disassembly of components and liability.

Neither the Python Intel installation nor the Classic Intel C/C++ Compiler are required.

- The Intel Fortran Compilers come in a combined installer providing both Classic and Beta versions; these also take around a gigabyte and a half or so.

We will consider the classic example of the generation of Fibonnaci numbers, `fib1.f`, given by:

    C FILE: FIB1.F
          SUBROUTINE FIB(A,N)
    C
    C     CALCULATE FIRST N FIBONACCI NUMBERS
    C
          INTEGER N
          REAL*8 A(N)
          DO I=1,N
             IF (I.EQ.1) THEN
                A(I) = 0.0D0
             ELSEIF (I.EQ.2) THEN
                A(I) = 1.0D0
             ELSE
                A(I) = A(I-1) + A(I-2)
             ENDIF
          ENDDO
          END
    C END FILE FIB1.F

For `cmd.exe` fans, using the Intel oneAPI command prompt is the easiest approach, as it loads the required environment for both `ifort` and `msvc`. Helper batch scripts are also provided.

    # cmd.exe
    "C:\Program Files (x86)\Intel\oneAPI\setvars.bat"
    python -m numpy.f2py -c fib1.f -m fib1
    python -c "import fib1; import numpy as np; a=np.zeros(8); fib1.fib(a); print(a)"

Powershell usage is a little less pleasant, and this configuration now works with MSVC as:

    # Powershell
    python -m numpy.f2py -c fib1.f -m fib1 --f77exec='C:\Program Files (x86)\Intel\oneAPI\compiler\latest\windows\bin\intel64\ifort.exe' --f90exec='C:\Program Files (x86)\Intel\oneAPI\compiler\latest\windows\bin\intel64\ifort.exe' -L'C:\Program Files (x86)\Intel\oneAPI\compiler\latest\windows\compiler\lib\ia32'
    python -c "import fib1; import numpy as np; a=np.zeros(8); fib1.fib(a); print(a)"
    # Alternatively, set environment and reload Powershell in one line
    cmd.exe /k '"C:\Program Files (x86)\Intel\oneAPI\setvars.bat" && powershell'
    python -m numpy.f2py -c fib1.f -m fib1
    python -c "import fib1; import numpy as np; a=np.zeros(8); fib1.fib(a); print(a)"

Note that the actual path to your local installation of ifort may vary, and the command above will need to be updated accordingly.