feat: added get_numpy_attribute_type_from_iterable()

Author: ntamas

src/igraph_ctypes/_internal/types.py

@@ -49,6 +49,7 @@ def vector_fields(base_type):
 np_type_of_igraph_bool_t = np.bool_
 np_type_of_igraph_integer_t = np.int64
 np_type_of_igraph_real_t = np.float64
+np_type_of_igraph_string = np.string_
 np_type_of_igraph_uint_t = np.uint64
 
 

src/igraph_ctypes/_internal/utils.py

@@ -1,8 +1,16 @@
+import numpy as np
+
 from ctypes import byref, cast, c_char_p, c_ubyte, POINTER, sizeof
 from functools import wraps
-from typing import Callable, Union
+from numpy.typing import DTypeLike
+from typing import Any, Callable, Iterable, Union
 
 from .errors import python_exception_to_igraph_error_t
+from .types import (
+    np_type_of_igraph_bool_t,
+    np_type_of_igraph_real_t,
+    np_type_of_igraph_string,
+)
 
 __all__ = ("bytes_to_str", "get_raw_memory_view", "nop", "protect", "protect_with")
 
@@ -21,6 +29,57 @@ def bytes_to_str(
         return value.decode(encoding, errors)
 
 
+def get_numpy_attribute_type_from_iterable(  # noqa: C901
+    it: Iterable[Any],
+) -> DTypeLike:
+    """Determines the appropriate NumPy datatype to store all the items found in
+    the given iterable as an attribute.
+
+    This means that this function basically classifies the iterable into one of
+    the following data types:
+
+    - np_type_of_igraph_bool_t for Boolean attributes
+    - np_type_of_igraph_real_t for numeric attributes
+    - np_type_of_igraph_string for string attributes
+    - np.object_ for any other (mixed) attribute type
+
+    When the iterable is empty, a numeric attribute will be assumed.
+    """
+    it = iter(it)
+    try:
+        item = next(it)
+    except StopIteration:
+        # Iterable empty
+        return np_type_of_igraph_real_t
+
+    best_fit: DTypeLike
+    if isinstance(item, bool):
+        best_fit = np_type_of_igraph_bool_t
+    elif isinstance(item, (int, float, np.number)):
+        best_fit = np_type_of_igraph_real_t
+    elif isinstance(item, str):
+        best_fit = np_type_of_igraph_string
+    else:
+        return np.object_
+
+    for item in it:
+        if isinstance(item, bool):
+            if best_fit == np_type_of_igraph_string:
+                return np.object_
+        elif isinstance(item, (int, float, np.number)):
+            if best_fit == np_type_of_igraph_string:
+                return np.object_
+            else:
+                best_fit = np_type_of_igraph_real_t
+        elif isinstance(item, str):
+            if best_fit != np_type_of_igraph_string:
+                return np.object_
+        else:
+            return np.object_
+
+    return best_fit
+
+
 def get_raw_memory_view(obj):
     """Returns a view into the raw bytes of a ctypes object."""
     return cast(byref(obj), POINTER(c_ubyte * sizeof(obj))).contents

tests/test_utils.py

@@ -0,0 +1,35 @@
+from numpy import inf, nan, object_
+
+from igraph_ctypes._internal.types import (
+    np_type_of_igraph_bool_t,
+    np_type_of_igraph_string,
+    np_type_of_igraph_real_t,
+)
+from igraph_ctypes._internal.utils import get_numpy_attribute_type_from_iterable
+
+from pytest import mark
+
+
+get = get_numpy_attribute_type_from_iterable
+
+
+@mark.parametrize(
+    ("input", "expected"),
+    [
+        ((), np_type_of_igraph_real_t),
+        ((17, -2), np_type_of_igraph_real_t),
+        ((17.5, -3.5), np_type_of_igraph_real_t),
+        ((inf, -3.5, nan), np_type_of_igraph_real_t),
+        ((False, True), np_type_of_igraph_bool_t),
+        ((False, 123, True), np_type_of_igraph_real_t),
+        ((123, False, True), np_type_of_igraph_real_t),
+        (("spam", "ham", "bacon"), np_type_of_igraph_string),
+        (("spam", 123), object_),
+        ((123, "spam"), object_),
+        ((None,), object_),
+        (("spam", False), object_),
+        ((123, None), object_),
+    ],
+)
+def test_empty(input, expected):
+    assert get(input) == expected