How to declare types for class attributes?

Question

How to declare class attribute types? For example, in the below class, how to declare self.number as an unsinged int type?

Attempting to declare it this way:

class A:    

    def __init__(self):
        cdef unsigned int self.number
        self.number = 4
        print(type(self.number), self.number)

Results in this error:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-34-80176274b668> in <module>
----> 1 get_ipython().run_cell_magic('cython', '', 'class A:    \n    \n    def __init__(self):\n        cdef unsigned int self.number\n        self.number = 4\n        print(type(self.number), self.number)\n')

~/anaconda3/lib/python3.7/site-packages/IPython/core/interactiveshell.py in run_cell_magic(self, magic_name, line, cell)
   2321             magic_arg_s = self.var_expand(line, stack_depth)
   2322             with self.builtin_trap:
-> 2323                 result = fn(magic_arg_s, cell)
   2324             return result
   2325 

<decorator-gen-127> in cython(self, line, cell)

~/anaconda3/lib/python3.7/site-packages/IPython/core/magic.py in <lambda>(f, *a, **k)
    185     # but it's overkill for just that one bit of state.
    186     def magic_deco(arg):
--> 187         call = lambda f, *a, **k: f(*a, **k)
    188 
    189         if callable(arg):

~/anaconda3/lib/python3.7/site-packages/Cython/Build/IpythonMagic.py in cython(self, line, cell)
    323         if need_cythonize:
    324             extensions = self._cythonize(module_name, code, lib_dir, args, quiet=args.quiet)
--> 325             assert len(extensions) == 1
    326             extension = extensions[0]
    327             self._code_cache[key] = module_name

TypeError: object of type 'NoneType' has no len()

A solution to another question, which declares the attribute type at the top of the class definition also fails:

class A:
    cdef unsigned int number

    def __init__(self):
        self.number = 4
        print(type(self.number), self.number)

It results in the below error:

Error compiling Cython file:
------------------------------------------------------------
...
class A:
    cdef unsigned int number
        ^
------------------------------------------------------------

/home/greg/.cache/ipython/cython/_cython_magic_48a1f134ce2732274c6f5bdb1c477e52.pyx:2:9: cdef statement not allowed here

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-35-0af4c38224f5> in <module>
----> 1 get_ipython().run_cell_magic('cython', '', 'class A:\n    cdef unsigned int number\n    \n    def __init__(self):\n        self.number = 4\n        print(type(self.number), self.number)\n')

~/anaconda3/lib/python3.7/site-packages/IPython/core/interactiveshell.py in run_cell_magic(self, magic_name, line, cell)
   2321             magic_arg_s = self.var_expand(line, stack_depth)
   2322             with self.builtin_trap:
-> 2323                 result = fn(magic_arg_s, cell)
   2324             return result
   2325 

<decorator-gen-127> in cython(self, line, cell)

~/anaconda3/lib/python3.7/site-packages/IPython/core/magic.py in <lambda>(f, *a, **k)
    185     # but it's overkill for just that one bit of state.
    186     def magic_deco(arg):
--> 187         call = lambda f, *a, **k: f(*a, **k)
    188 
    189         if callable(arg):

~/anaconda3/lib/python3.7/site-packages/Cython/Build/IpythonMagic.py in cython(self, line, cell)
    323         if need_cythonize:
    324             extensions = self._cythonize(module_name, code, lib_dir, args, quiet=args.quiet)
--> 325             assert len(extensions) == 1
    326             extension = extensions[0]
    327             self._code_cache[key] = module_name

TypeError: object of type 'NoneType' has no len()

How to declare attribute types for a Python class?

Why is the first example from the documentation (https://cython.readthedocs.io/en/latest/src/userguide/extension_types.html#introduction) not an option for you? — ead, Apr 01 '19 at 07:03
@ead The class needs to be accessible from Python and`cdef class` doesn't seem to allow that — Greg, Apr 01 '19 at 07:06
Ok, that was not clear from your question. What about the second example in the documentation: https://cython.readthedocs.io/en/latest/src/userguide/extension_types.html#static-attributes? — ead, Apr 01 '19 at 07:08
@ead Thank you, think that's the answer, subclassing the cdef class in cython — Greg, Apr 01 '19 at 07:20
Possible duplicate of [Mixing cdef and regular python attributes in cdef class](https://stackoverflow.com/questions/42632297/mixing-cdef-and-regular-python-attributes-in-cdef-class) — ead, Apr 12 '19 at 11:06

How to declare types for class attributes?

0 Answers0