Vfrdtyky

I want to build a function that can return the most common permutation of six "R" letters plus six "B" letters, the list may looks like this:

a = ['R'] * 6 + ['B'] * 6

random.shuffle(a)

shuffle = ''.join(a)

shuffle

Output: 'BRBRRRBBRBBR'

I want to write a loop of this function to simulate the most common distribution of these strings. I did write a for loop with python and it did work, but after I import cython to accelerate this function, something goes wrong, here is the code:

'''Python Code'''

import random

def random_loop_py(times):

    a = ['R'] * 6 + ['B'] * 6

    count = {}

    for i in range(times):

        random.shuffle(a)

        shuffle = ''.join(a)

        if shuffle in count.keys():

            count[shuffle] += 1

        else:

            count[shuffle] = 1

    return count

%timeit random_loop_py(100000)



'''Cython Code'''

    %load_ext cython

    %%cython

    import random

    cpdef void random_loop(int size):

        a = ['R'] * 6 + ['B'] * 6

        count = {}

        for i in range(size):

            random.shuffle(a)

            shuffle = ''.join(a)

            if shuffle in count.keys():

                count[shuffle] += 1

            else:

                count[shuffle] = 1

        return count.values()

And Error:

Error compiling Cython file:

------------------------------------------------------------

...

        shuffle = ''.join(a)

        if shuffle in count.keys():

            count[shuffle] += 1

        else:

            count[shuffle] = 1

    return count.keys()

                    ^

------------------------------------------------------------



/Users/lee_excited/.ipython/cython/_cython_magic_e70ad62499224c5d4fd4e23d6dcb9e49.pyx:12:21: Return with value in void function

---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

<ipython-input-120-a09f2e5d5e69> in <module>

----> 1 get_ipython().run_cell_magic('cython', '', "import randomncpdef void random_loop(int size):n    a = ['R'] * 6 + ['B'] * 6n    count = {}n    for i in range(size):n        random.shuffle(a)n        shuffle = ''.join(a)n        if shuffle in count.keys():n            count[shuffle] += 1n        else:n            count[shuffle] = 1n    return count.keys()n")



~/anaconda3/lib/python3.6/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/python3.6/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/python3.6/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()

What kind of data should I return to accelerate my simulation, please?

Your function has a void return type:

cpdef void random_loop(int size):

    ...

    return count.values()

Consequently, you are not supposed to return anything from it, and the exception message is very clear on that. Change the return type to list:

cpdef list random_loop(int size):

    ...

    return list(count.values())

P.S.

Your function is not very Cython-friendly: I don't think you will get significant performance improvements.

Update

I can't reproduce your error after the fix

In [9]: %%cython

   ...: import random

   ...: cpdef list random_loop(int size):

   ...:     a = ['R'] * 6 + ['B'] * 6

   ...:     count = {}

   ...:     for i in range(size):

   ...:         random.shuffle(a)

   ...:         shuffle = ''.join(a)

   ...:         if shuffle in count.keys():

   ...:             count[shuffle] += 1

   ...:         else:

   ...:             count[shuffle] = 1

   ...:     return list(count.values())

   ...: 



In [10]: random_loop(10)

Out[10]: [1, 1, 1, 1, 1, 1, 1, 1, 1, 1]

As you can see, it compiles perfectly fine.