numpy.dtype — NumPy v1.15 Manual (original) (raw)

class numpy. dtype(obj, align=False, copy=False)[source]¶

Create a data type object.

A numpy array is homogeneous, and contains elements described by a dtype object. A dtype object can be constructed from different combinations of fundamental numeric types.

Examples

Using array-scalar type:

np.dtype(np.int16) dtype('int16')

Structured type, one field name ‘f1’, containing int16:

np.dtype([('f1', np.int16)]) dtype([('f1', '<i2')])

Structured type, one field named ‘f1’, in itself containing a structured type with one field:

np.dtype([('f1', [('f1', np.int16)])]) dtype([('f1', [('f1', '<i2')])])

Structured type, two fields: the first field contains an unsigned int, the second an int32:

np.dtype([('f1', np.uint), ('f2', np.int32)]) dtype([('f1', '<u4'), ('f2', '<i4')])

Using array-protocol type strings:

np.dtype([('a','f8'),('b','S10')]) dtype([('a', '<f8'), ('b', '|S10')])

Using comma-separated field formats. The shape is (2,3):

np.dtype("i4, (2,3)f8") dtype([('f0', '<i4'), ('f1', '<f8', (2, 3))])

Using tuples. int is a fixed type, 3 the field’s shape. voidis a flexible type, here of size 10:

np.dtype([('hello',(int,3)),('world',np.void,10)]) dtype([('hello', '<i4', 3), ('world', '|V10')])

Subdivide int16 into 2 int8’s, called x and y. 0 and 1 are the offsets in bytes:

np.dtype((np.int16, {'x':(np.int8,0), 'y':(np.int8,1)})) dtype(('<i2', [('x', '|i1'), ('y', '|i1')]))

Using dictionaries. Two fields named ‘gender’ and ‘age’:

np.dtype({'names':['gender','age'], 'formats':['S1',np.uint8]}) dtype([('gender', '|S1'), ('age', '|u1')])

Offsets in bytes, here 0 and 25:

np.dtype({'surname':('S25',0),'age':(np.uint8,25)}) dtype([('surname', '|S25'), ('age', '|u1')])

| Attributes: | alignment The required alignment (bytes) of this data-type according to the compiler. More information is available in the C-API section of the manual. base byteorder A character indicating the byte-order of this data-type object. One of: ‘=’ native ‘<’ little-endian ‘>’ big-endian ‘|’ not applicable All built-in data-type objects have byteorder either ‘=’ or ‘|’. >>> dt = np.dtype('i2') >>> dt.byteorder '=' >>> # endian is not relevant for 8 bit numbers >>> np.dtype('i1').byteorder '|' >>> # or ASCII strings >>> np.dtype('S2').byteorder '|' >>> # Even if specific code is given, and it is native >>> # '=' is the byteorder >>> import sys >>> sys_is_le = sys.byteorder == 'little' >>> native_code = sys_is_le and '<' or '>' >>> swapped_code = sys_is_le and '>' or '<' >>> dt = np.dtype(native_code + 'i2') >>> dt.byteorder '=' >>> # Swapped code shows up as itself >>> dt = np.dtype(swapped_code + 'i2') >>> dt.byteorder == swapped_code True char A unique character code for each of the 21 different built-in types. descr PEP3118 interface description of the data-type. fields Dictionary of named fields defined for this data type, or None. flags Bit-flags describing how this data type is to be interpreted. Bit-masks are in numpy.core.multiarray as the constants_ITEM_HASOBJECT_, LIST_PICKLE, ITEM_IS_POINTER, NEEDS_INIT,NEEDS_PYAPI, USE_GETITEM, USE_SETITEM. A full explanation of these flags is in C-API documentation; they are largely useful for user-defined data-types. hasobject Boolean indicating whether this dtype contains any reference-counted objects in any fields or sub-dtypes. isalignedstruct Boolean indicating whether the dtype is a struct which maintains field alignment. isbuiltin Integer indicating how this dtype relates to the built-in dtypes. isnative Boolean indicating whether the byte order of this dtype is native to the platform. itemsize The element size of this data-type object. For 18 of the 21 types this number is fixed by the data-type. For the flexible data-types, this number can be anything. kind A character code (one of ‘biufcmMOSUV’) identifying the general kind of data. b boolean i signed integer u unsigned integer f floating-point c complex floating-point m timedelta M datetime O object S (byte-)string U Unicode V void metadata name A bit-width name for this data-type. names Ordered list of field names, or None if there are no fields. ndim Number of dimensions of the sub-array if this data type describes a sub-array, and 0 otherwise. num A unique number for each of the 21 different built-in types. These are roughly ordered from least-to-most precision. shape Shape tuple of the sub-array if this data type describes a sub-array, and () otherwise. str The array-protocol typestring of this data-type object. subdtype Tuple (item_dtype, shape) if this dtype describes a sub-array, and None otherwise. type The type object used to instantiate a scalar of this data-type. | | ----------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |

Methods