NumPy

numpy.promote_types

numpy.promote_types(type1, type2)

Returns the data type with the smallest size and smallest scalar kind to which both type1 and type2 may be safely cast. The returned data type is always in native byte order.

This function is symmetric, but rarely associative.

Parameters
type1dtype or dtype specifier

First data type.

type2dtype or dtype specifier

Second data type.

Returns
outdtype

The promoted data type.

Notes

New in version 1.6.0.

Starting in NumPy 1.9, promote_types function now returns a valid string length when given an integer or float dtype as one argument and a string dtype as another argument. Previously it always returned the input string dtype, even if it wasn’t long enough to store the max integer/float value converted to a string.

Examples

>>> np.promote_types('f4', 'f8')
dtype('float64')
>>> np.promote_types('i8', 'f4')
dtype('float64')
>>> np.promote_types('>i8', '<c8')
dtype('complex128')
>>> np.promote_types('i4', 'S8')
dtype('S11')

An example of a non-associative case:

>>> p = np.promote_types
>>> p('S', p('i1', 'u1'))
dtype('S6')
>>> p(p('S', 'i1'), 'u1')
dtype('S4')

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