README.rst

cdatastructs

Simple data structures accessible from both Python and C. Data in structures are stored as a primitive C types, so in C you can compute data without Python overhead.

Python code:

>>> import array
>>> import itertools
>>> import math
>>> import random

>>> from cdatastructs.hashmap import Int2Int

>>> from my_c_extension import calculate_data

# Create instance of the Int2Int - mapping from ID
# to position in array
>>> id2index = Int2Int()

# Fill id2index, it is mapping, so you can use it same as dict
>>> id2index[72351277] = 0
>>> id2index[98092127498] = 1
>>> id2index[126987499] = 2
>>> id2index[36] = 3
>>> id2index[980980] = 4
>>> len(id2index)
5
>>> id2index[980980]
4
>>> id2index.buffer_ptr
94691713534960

# Prepare two arrays with numbers for calculate and one array for results
>>> a = array.array('d', (random.random() for _ in id2index))
>>> b = array.array('d', (random.random() for _ in id2index))
>>> results = array.array('d', (math.nan for _ in id2index))

# Calculate data for IDs 98092127498, 126987499 and 36
>>> ids = array.array('Q', [98092127498, 126987499, 36])
>>> calculate_data(id2index, ids, a, b, results)

# Obtain result
>>> results[id2index[72351277]]
nan
>>> results[id2index[98092127498]]
0.8163673050897404

C code:

#include <hashmap.h>

static PyObject * my_c_extension_compute_data(
        PyObject *id2index, PyObject *args) {

    Int2IntHashTable_t *id2position;
    unsigned long long *ids;
    size_t *ids_count;
    double *a;
    double *b;
    double *res;

    // Parse args, obtain pointers to buffers and cast them to C types
    ...

    // Calculate data, there are only pure C types, no Python overhead
    for (size_t i=0; i<ids_count; ++i) {
        unsigned long long id = ids[i];
        size_t *position;
        if (int2int_get(id2position, id, position) != 0) {
            goto error;
        }
        res[*position] = a[*position] + b[*position];
    }

    ...
    Py_RETURN_NONE;
error:
    ...
    return NULL;
}

See demos/ for more examples and details.

License

3-clause BSD