Pure python array decoding example.

Fix for agronholm#32
Does not require Numpy, can't handle 128bit floating point.

examples/array_codec.py

@@ -0,0 +1,106 @@
+import array
+import sys
+from binascii import unhexlify
+from pprint import pprint
+
+import cbor2
+
+
+def is_float(tag):
+    return tag >> 4 & 1
+
+
+def is_signed(tag):
+    return tag >> 3 & 1
+
+
+def is_le(tag):
+    return tag >> 2 & 1
+
+
+def needs_swap(tag):
+    length = tag & 0b11
+    if is_float(tag) == 0 and length == 0:
+        return False
+    if sys.byteorder == 'big':
+        return is_le(tag)
+    else:
+        return not is_le(tag)
+
+
+def tag_to_type(tag):
+    int_typecodes = ['B', 'H', 'L', 'Q']
+    sint_typecodes = [n.lower() for n in int_typecodes]
+    float_typecodes = [None, 'f', 'd', None]
+    length = tag & 0b11
+    if is_float(tag):
+        return float_typecodes[length]
+    elif is_signed(tag):
+        return sint_typecodes[length]
+    else:
+        return int_typecodes[length]
+
+
+def create_encode_map():
+    encode_map = {}
+    for tag in ARRAY_TAGS:
+        if needs_swap(tag):
+            continue
+        typecode = tag_to_type(tag)
+        if typecode is None:
+            continue
+        if typecode not in encode_map:
+            encode_map[typecode] = tag
+    return encode_map
+
+
+ARRAY_TAGS = range(64, 88)
+ENCODE_MAP = create_encode_map()
+
+
+def default(encoder, obj):
+    if isinstance(obj, array.array):
+        tag = ENCODE_MAP[obj.typecode]
+        encoder.encode(cbor2.CBORTag(tag, obj.tobytes()))
+    elif isinstance(obj, memoryview):
+        tag = ENCODE_MAP[obj.format]
+        encoder.encode(cbor2.CBORTag(tag, obj.tobytes()))
+
+
+def my_hook(decoder, tag):
+    if tag.tag in ARRAY_TAGS:
+        dtype = tag_to_type(tag.tag)
+        if dtype is None:
+            return tag
+        value = array.array(dtype, tag.value)
+        if needs_swap(tag.tag):
+            value.byteswap()
+        return value
+    else:
+        return tag
+
+
+def selftest():
+    mydata = {
+        'sint8': array.array('b', range(-3, 1)),
+        'uint8': array.array('B', range(3)),
+        'uint16': array.array('H', [n + 128 for n in range(3)]),
+        'sint16': array.array('h', [n - 256 for n in range(3)]),
+        'sint32': array.array('l', [n - 2 ** 15 for n in range(3)]),
+        'uint32': array.array('L', [n + 2 ** 16 for n in range(3)]),
+        'uint64': array.array('Q', [n + 2 ** 32 for n in range(3)]),
+        'sint64': array.array('q', [n - 2 ** 31 for n in range(3)]),
+        'float32': array.array('f', [2 ** (1 / n) for n in range(1, 4)]),
+        'float64': array.array('d', [2 ** (1 / n) for n in range(1, 4)]),
+    }
+
+    pprint(cbor2.loads(cbor2.dumps(mydata, default=default), tag_hook=my_hook))
+    pprint(ENCODE_MAP)
+
+    pprint(cbor2.loads(cbor2.dumps(cbor2.CBORTag(87, bytes(16))), tag_hook=my_hook))
+
+    pprint(cbor2.loads(unhexlify(b'd8514c400000003fb504f33fa14518'), tag_hook=my_hook))
+
+
+if __name__ == '__main__':
+    selftest()