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Methods vs functions in NumPy

Many things are implemented in NumPy as both functions and methods. For example, there is a np.sum function, that adds up all the elements:

>>> import numpy as np

>>> arr = np.array([1, 2, 0, 1])
>>> np.sum(arr)
4

There is also a sum method of the numpy array object:

>>> type(arr)
<class 'numpy.ndarray'>

>>> arr.sum()
4

Nearly all the method versions do the same thing as the function versions. Examples are mean, min, max, sum, reshape. Choosing the method or the function will usually depend on which one is easier to read.