NumPy require() Method

The NumPy's require() method returns a ndarray that satisfies certain requirements.

The numpy.require() method is useful for ensuring that an array has the correct flags, thereby satisfying the requirements for passing it to compiled code, possibly through ctypes.

Syntax

Syntax: numpy.require(a, dtype=None, requirements=None)

Parameters:

• a :  array_like
• dtype : data-type

requirements : str or list of str 

The requirements list can be any of the following.

• 'F' : ‘F_CONTIGUOUS’  - ensure a Fortran-contiguous array.
• 'C'  : ‘C_CONTIGUOUS’ - ensure a C-contiguous array.
• 'A' : 'ALIGNED’  - ensure a data-type aligned array.
• 'W’ : ‘WRITABLE’  - ensure a writable array.
• ‘O’ : ‘OWNDATA’ - ensure an array that owns its own data.
• ‘E’ : ‘ENSUREARRAY’ - ensure a base array, instead of a subclass.

Returns :  ndarray

Exception : ValueError - Raises ValueError

Examples

Let's look at some examples to understand require() method of the NumPy library in Python.

Example 1:

# Python program explaining
# numpy.require() function

# importing numpy
import numpy as np

# creating 4 x 4 array
data = np.arange(16).reshape(4, 4)

data.flags

Output:

C_CONTIGUOUS : True
  F_CONTIGUOUS : False
  OWNDATA : False
  WRITABLE : True
  ALIGNED : True
  WRITEBACKIFCOPY : False
  UPDATEIFCOPY : False

Example 2:

import numpy as np

# Python program explaining
# numpy.require()
b = np.require(data, dtype=np.float32,
               requirements=['A', 'W', 'O', 'C'])
b.flags

Output:

C_CONTIGUOUS : True
  F_CONTIGUOUS : False
  OWNDATA : True
  WRITABLE : True
  ALIGNED : True
  WRITEBACKIFCOPY : False
  UPDATEIFCOPY : False