How to Fix the AttributeError: 'numpy.ndarray' Object Has No Attribute 'Append' in Python

1. the AttributeError: 'numpy.ndarray' object has no attribute 'append' in Python
2. Fix the AttributeError: 'numpy.ndarray' object has no attribute 'append' in Python

Like lists or arrays, NumPy doesn’t have the append() method for the array; instead, we need to use the append() method from NumPy. We can add multiple NumPy arrays using the append() method.

the AttributeError: 'numpy.ndarray' object has no attribute 'append' in Python

ndarray is an n-dimensional NumPy array, which is useful for various purposes, like when we have multiple data types for a model. Here’s a simple example using this:

import numpy as np

arr = np.array([[1, 2, 3], [4, 5, 6]])
print(f"Type: {type(arr)}")
print(f"Dimension: {arr.ndim}")
print(f"Shape: {arr.shape}")
print(f"Element data type: {arr.dtype}")

Output:

Type: <class 'numpy.ndarray'>
Dimension: 2
Shape: (2, 3)
Element data type: int32

Now, let’s try to append an array in the ndarray object above. We will get the following error:

>>> arr.append([1,2])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'numpy.ndarray' object has no attribute 'append'

So, it is clear that the ndarray type object doesn’t contain any method called append().

Fix the AttributeError: 'numpy.ndarray' object has no attribute 'append' in Python

To append a new array in the ndarray object, we need to ensure that the new array has the same dimension as the previous one inside the ndarray.

Here’s how we will append the ndarray:

import numpy as np

arr = np.array([[1, 2, 3], [4, 5, 6]])
arr = np.append(arr, [[7, 8, 9]], axis=0)
print(arr)

Output:

[[1 2 3]
 [4 5 6]
 [7 8 9]]

Here, if you notice, we put the axis as 0. Now, if we didn’t mention the axis, then this will happen:

import numpy as np

arr = np.array([[1, 2, 3], [4, 5, 6]])
arr = np.append(arr, [[7, 8, 9]])
print(arr)

Output:

[1 2 3 4 5 6 7 8 9]

It just unwrapped all the elements and then made it one array!

Now, let’s observe what happens if we give an array that doesn’t have the same dimension:

import numpy as np

arr = np.array([[1, 2, 3], [4, 5, 6]])
arr = np.append(arr, [[7, 8]], axis=0)

Output:

ValueError: all the input array dimensions for the concatenation axis must match exactly, but along dimension 1, the array at index 0 has size 3 and the array at index 1 has a size 2

Here we got the ValueError for the dimension mismatch. To know more about the ndarray of NumPy, visit this blog.