Python 来自字符串名称的 CFFI 枚举

Question

我在 Python cffi 中定义了一个枚举。如何按名称实例化它？ The docs say how to get the string name from enum，但不是如何创建它。

ffibuilder = FFI()

ffibuilder.cdef('typedef enum { dense, sparse } dimension_mode;')

dim = ffibuilder.new('dimension_mode', 'sparse')
# E  TypeError: expected a pointer or array ctype, got 'dimension_mode'

Answer 1

您需要调用 dlopen('c') 将枚举加载到 C 命名空间。

>>> from cffi import FFI
>>> ffibuilder = FFI()
>>> ffibuilder.cdef('typedef enum { dense, sparse } dimension_mode;')
>>> dim = ffibuilder.new('dimension_mode', 'sparse')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/anaconda3/lib/python3.6/site-packages/cffi/api.py", line 258, in new
    return self._backend.newp(cdecl, init)
TypeError: expected a pointer or array ctype, got 'dimension_mode'

调用 dlopen()：

>>> c = ffibuilder.dlopen('c')

现在，access/assign 枚举值：

>>> c.dense
0
>>> c.sparse
1
>>>

来自ffi docs：

You can use the library object to call the functions previously declared by ffi.cdef(), to read constants, and to read or write global variables. Note that you can use a single cdef() to declare functions from multiple libraries, as long as you load each of them with dlopen() and access the functions from the correct one.

The libpath is the file name of the shared library, which can contain a full path or not (in which case it is searched in standard locations, as described in man dlopen), with extensions or not. Alternatively, if libpath is None, it returns the standard C library (which can be used to access the functions of glibc, on Linux).

Python 来自字符串名称的 CFFI 枚举

Python CFFI enum from string name

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