In [1]: import numpy as np ...: import c_module In [2]: a = np.arange(20.).reshape(4,5) ...: c_module.inc_array(a, 1.1) ...: print(a) from inc_array dimensions: 2, type: 12 [[ 1.1 2.1 3.1 4.1 5.1] [ 6.1 7.1 8.1 9.1 10.1] [11.1 12.1 13.1 14.1 15.1] [16.1 17.1 18.1 19.1 20.1]] In [3]: a = np.arange(20.).reshape(4,5) ...: c_module.not_inc_array(a, 1.1) ...: print(a) from not_inc_array dimensions: 2, type: 12 [[ 0. 1. 2. 3. 4.] [ 5. 6. 7. 8. 9.] [10. 11. 12. 13. 14.] [15. 16. 17. 18. 19.]]