传递布尔数组而不用 `f2py` 复制？

Question

如果我打算用 f2py 向 Fortran 变量传递一个布尔值 NumPy 数组，应该如何键入它们？ integer*1和logical*1我都试过了，但是这两个都表明数组被复制了。

例如，如果我编译文件，foo.f95，包含：

subroutine foo(x, n)
    logical*1 x(n)
    !f2py intent(in) x
    !f2py intent(hide), depend(x) :: n=shape(x,0)
    ...
end subroutine

与 f2py -c -m foo foo.f90 -DF2PY_REPORT_ON_ARRAY_COPY=1 和运行类似：

import numpy as np
import foo
x = np.random.randn(100) < 0
foo.foo(x)

它打印

copied an array: size=100, elsize=1

如果将 logical*1 更改为 integer*1，我会得到相同的结果。 Fortran 文件中布尔数组的正确类型是什么，这样数组就不会被复制？

请注意，这不是内存连续性问题，因为数组是一维的——foo.foo(np.asfortranarray(x)) 打印相同的复制消息。

Answer 1

从一些实验(*)来看，似乎 Python/f2py 将 np.int8 视为与 logical*1 兼容，而 np.bool 或 np.bool8 对某些人不兼容原因。将 print *, "(fort) x = ", x 插入 foo.f90 后，我们得到：

>>> foo.foo( np.array( [ True, False, False ], dtype=np.bool ) )
copied an array: size=3, elsize=1
 (fort) x =  T F F
>>> foo.foo( np.array( [ False, True, False ], dtype=np.bool8 ) )
copied an array: size=3, elsize=1
 (fort) x =  F T F
>>> foo.foo( np.array( [ False, False, True ], dtype=np.int8 ) ) # no copy
 (fort) x =  F F T

因为 True 和 False 只是简单地映射到 1 和 0，所以在 Python 端使用 int8 数组可能会很方便。

(*) 一些实验

这里，我把f2py intent注释改成了inout，看看我们是否可以从Fortran端修改数组。

foo.f90:

subroutine foo(x, n)
    use iso_c_binding
    implicit none
    integer n
    logical*1 x( n )
    ! logical x( n )
    ! logical(c_bool) x( n )

    !f2py intent(inout) x
    !f2py intent(hide), depend(x) :: n=shape(x,0)

    print *, "(fort) x = ", x
    print *, "(fort) sizeof(x(1)) = ", sizeof(x(1))
    print *, "(fort) resetting x(:) to true"
    x(:) = .true.
end subroutine

test.py:

import numpy as np
import foo

for T in [ np.bool, np.bool8,
           np.int,  np.int8,  np.int32,  np.int64,
           np.uint, np.uint8, np.uint32, np.uint64,
           np.dtype('b'), np.dtype('int8'), np.dtype('int32') ]:

    print( "-------------------------" )
    print( "dtype =", T )

    x = np.array( [ True, False, True ], dtype=T )
    print( "input x =", x )

    try:
        foo.foo( x )
        print( "output x =", x )
    except:
        print( "failed" )

logical*1 的结果：

-------------------------
dtype = <class 'bool'>
input x = [ True False  True]
failed
-------------------------
dtype = <class 'numpy.bool_'>
input x = [ True False  True]
failed
-------------------------
dtype = <class 'int'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.int8'>
input x = [1 0 1]
 (fort) x =  T F T
 (fort) sizeof(x(1)) =                     1
 (fort) resetting x(:) to true
output x = [1 1 1]
-------------------------
dtype = <class 'numpy.int32'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.int64'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.uint64'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.uint8'>
input x = [1 0 1]
 (fort) x =  T F T
 (fort) sizeof(x(1)) =                     1
 (fort) resetting x(:) to true
output x = [1 1 1]
-------------------------
dtype = <class 'numpy.uint32'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.uint64'>
input x = [1 0 1]
failed
-------------------------
dtype = int8
input x = [1 0 1]
 (fort) x =  T F T
 (fort) sizeof(x(1)) =                     1
 (fort) resetting x(:) to true
output x = [1 1 1]
-------------------------
dtype = int8
input x = [1 0 1]
 (fort) x =  T F T
 (fort) sizeof(x(1)) =                     1
 (fort) resetting x(:) to true
output x = [1 1 1]
-------------------------
dtype = int32
input x = [1 0 1]
failed

logical 的结果（默认种类）：

-------------------------
dtype = <class 'bool'>
input x = [ True False  True]
failed
-------------------------
dtype = <class 'numpy.bool_'>
input x = [ True False  True]
failed
-------------------------
dtype = <class 'int'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.int8'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.int32'>
input x = [1 0 1]
 (fort) x =  T F T
 (fort) sizeof(x(1)) =                     4
 (fort) resetting x(:) to true
output x = [1 1 1]
-------------------------
dtype = <class 'numpy.int64'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.uint64'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.uint8'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.uint32'>
input x = [1 0 1]
 (fort) x =  T F T
 (fort) sizeof(x(1)) =                     4
 (fort) resetting x(:) to true
output x = [1 1 1]
-------------------------
dtype = <class 'numpy.uint64'>
input x = [1 0 1]
failed
-------------------------
dtype = int8
input x = [1 0 1]
failed
-------------------------
dtype = int8
input x = [1 0 1]
failed
-------------------------
dtype = int32
input x = [1 0 1]
 (fort) x =  T F T
 (fort) sizeof(x(1)) =                     4
 (fort) resetting x(:) to true
output x = [1 1 1]

结果 logical(c_bool)（通过 iso_c_binding）：

-------------------------
dtype = <class 'bool'>
input x = [ True False  True]
failed
-------------------------
dtype = <class 'numpy.bool_'>
input x = [ True False  True]
failed
-------------------------
dtype = <class 'int'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.int8'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.int32'>
input x = [1 0 1]
 (fort) x =  T F F
 (fort) sizeof(x(1)) =                     1
 (fort) resetting x(:) to true
output x = [65793     0     1]
-------------------------
dtype = <class 'numpy.int64'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.uint64'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.uint8'>
input x = [1 0 1]
failed
-------------------------
dtype = <class 'numpy.uint32'>
input x = [1 0 1]
 (fort) x =  T F F
 (fort) sizeof(x(1)) =                     1
 (fort) resetting x(:) to true
output x = [65793     0     1]
-------------------------
dtype = <class 'numpy.uint64'>
input x = [1 0 1]
failed
-------------------------
dtype = int8
input x = [1 0 1]
failed
-------------------------
dtype = int8
input x = [1 0 1]
failed
-------------------------
dtype = int32
input x = [1 0 1]
 (fort) x =  T F F
 (fort) sizeof(x(1)) =                     1
 (fort) resetting x(:) to true
output x = [65793     0     1]

出于某种原因，最后一个 logical(c_bool) 不适用于上述用法...（f2py 似乎将 logical(c_bool) 视为 4 个字节，而 gfortran 将其视为 1 个字节，所以不一致...)

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