NumPy and Pandas

Just curious about Numpy arrays when printed. Any reason why my output would lose the commas between the values? and why it doesn’t respond with the type being <class ‘numpy.ndarray’>?

import numpy as np
numbers2 = [
    [1,2,3,4,5],
    [6,7,8,9,0]
]
two_d = np.array(numbers2)
print(f"Two d: {two_d} is of type {two_d} with length {len(two_d)}\n")

Output:

Two d: [[1 2 3 4 5]
 [6 7 8 9 0]] is of type [[1 2 3 4 5]
 [6 7 8 9 0]] with length 2

Hi Dean,

Two things are going on here. First, NumPy’s array type has a custom __str__ method, which rightly or wrongly, they’ve decided to format so that when you do print(two_d) it shows the array as a readable, lined up thing. This means that when you put it inside of an f-string like you have it looks weird.

>>> import numpy as np
>>> a = [ [1,2,3,4,5], [6,7,8,9,0] ]
>>> d = np.array(a)
>>> d
array([[1, 2, 3, 4, 5],
       [6, 7, 8, 9, 0]])
>>> str(d)
'[[1 2 3 4 5]\n [6 7 8 9 0]]'
>>> print(d)
[[1 2 3 4 5]
 [6 7 8 9 0]]

The second thing is an error in your f-string. You’ve done “type {two_d}” when you meant to do “type {type(two_d)}”. The type of an array is exactly what you had expected. Continued from the same REPL session above:

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