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I have a quick question.

I would like to know if : array() is the same as []

An example:

Is :

[[1,2,2],[1,2,8]]

Equal to :

array([1,2,2],[1,2,8])

? Could you explain the differences and examples of uses pls.

My code :

import numpy as np
x = np.array(([1,2,2], [1,4,3], [1,2,9]))
x = np.full(x.shape, 10)
print(x)

I'm getting :

[[10,10,10],[10,10,10],[10,10,10]]

and I would like :

array([10,10,10], [10,10,10], [10,10,10])
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17
  • 2
    Does this answer your question? Python: Differences between lists and numpy array of objects Commented Mar 12, 2021 at 18:17
  • stackoverflow.com/questions/176011/… Commented Mar 12, 2021 at 18:18
  • 1
    The reason the initial comments didn't give any useful information is because the initial question wasn't asked in a useful way. Since you edited to include a minimal reproducible example, the question makes more sense. The reason you're seeing it without array() around is is the print() call. When you print an array, the repr is to just display the contents as a list of lists Commented Mar 12, 2021 at 18:36
  • 1
    @LuckyFr no array() does not == [[]]. You are merely seeing how numpy.ndarray objects are printed. Don't worry too much about what you see when you print something. Check the type of the object. You'll see your code produces a numpy.ndarray object, not a list, if that is what you are afraid of Commented Mar 12, 2021 at 18:54
  • 1
    @LuckyFr no. You can figure this out for yourself by running the code and checking the type Commented Mar 12, 2021 at 18:55

1 Answer 1

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A lot of the comments focused on the subject line, the difference between list and numpy array. But the example is all about the display of a numpy array.

Your example:

In [272]: x = np.array(([1,2,2], [1,4,3], [1,2,9]))
     ...: x = np.full(x.shape, 10)
In [273]: x
Out[273]: 
array([[10, 10, 10],
       [10, 10, 10],
       [10, 10, 10]])
In [274]: print(x)
[[10 10 10]
 [10 10 10]
 [10 10 10]]

That print is the str display of an array. Note the missing commas. The repr display includes the commas and word 'array'

In [275]: print(repr(x))
array([[10, 10, 10],
       [10, 10, 10],
       [10, 10, 10]])

The display of a list:

In [276]: x.tolist()
Out[276]: [[10, 10, 10], [10, 10, 10], [10, 10, 10]]

The 'duplicate' that focuses on list versus array:

Python: Differences between lists and numpy array of objects

Some examples from the comments:

In [277]: np.array()
Traceback (most recent call last):
  File "<ipython-input-277-e4f3b47dc252>", line 1, in <module>
    np.array()
TypeError: array() missing required argument 'object' (pos 1)

Making a 2d array without any elements:

In [278]: np.array([[]])
Out[278]: array([], shape=(1, 0), dtype=float64)

Making a 0d array with 1 element:

In [279]: np.array(34)
Out[279]: array(34)
In [280]: np.array(34).shape
Out[280]: ()

Arrays can a wide range of dimensions and shape, from 0d up (max 32). Depending on where you come from dimensions other than 2 can be hard to picture.

The display of arrays and lists generally match in the nesting of brackets.

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