Adventures in Machine Learning

Handling the ‘numpyndarray’ Append Error with npappend() and concatenate() functions

Handling the AttributeError: ‘numpy.ndarray’ object has no attribute ‘append’

If you are a beginner in Python programming, you may have encountered an error message that reads, “AttributeError: ‘numpy.ndarray’ object has no attribute ‘append’.” This error occurs when you try to use the append() function on a NumPy array. NumPy arrays are a data structure used in scientific computing to handle large amounts of data efficiently.

While they are similar to Python lists, they have some key differences – one of which is the inability to use append() as a means to add elements to the array. So, how can you fix this error?

Solution using np.append() instead of append()

Fortunately, NumPy provides us with an alternative function for adding elements to arrays – np.append(). This function is a universal function in NumPy and can be used to append elements to not only one-dimensional but also multi-dimensional arrays.

Unlike the append() function, np.append() creates a new array by concatenating the original array with the new elements.

Fixing the Error in Practice

Let’s create a NumPy array and see what happens when we try to append an element using the append() function. Our array will contain integers from 1 to 5.


import numpy as np

num_array = np.array([1,2,3,4,5])



This code results in the following error:


AttributeError: ‘numpy.ndarray’ object has no attribute ‘append’


The error message is straightforward – NumPy arrays do not have an append() method. We need to use np.append() instead.


new_array = np.append(num_array, 6)



Using np.append(), we have created a new array by concatenating the original array with the integer 6. The output gives us:


[1 2 3 4 5 6]


Using np.concatenate() for concatenating NumPy arrays to one another

What if we want to add elements from one NumPy array to another?

We can use the np.concatenate() function, which is a universal function in NumPy for concatenating arrays. “`python

num_array1 = np.array([1,2,3,4,5])

num_array2 = np.array([6,7,8,9,10])

concat_array = np.concatenate((num_array1, num_array2))



We have passed a tuple of arrays to np.concatenate() and concatenated them into a new array named concat_array. The final output is:


[ 1 2 3 4 5 6 7 8 9 10]



With this new knowledge of using np.append() and np.concatenate(), the error message “AttributeError: ‘numpy.ndarray’ object has no attribute ‘append'” should no longer be an issue. Remember to always use NumPy methods to manipulate NumPy arrays to avoid encountering errors.

As you progress in your Python programming journey, you will find that understanding the available tools at your disposal is critical in becoming an efficient programmer.

Additional Resources

While this article has provided a basic understanding of how to handle the “AttributeError: ‘numpy.ndarray’ object has no attribute ‘append'” error message when working with NumPy arrays, there is always more to learn. In this section, we will explore additional resources that can help increase your knowledge of the append() and concatenate() functions in NumPy.

NumPy Append() Documentation

The official NumPy documentation for the append() function can be found on the NumPy website at This documentation provides detailed information about the function’s parameters, return value, and examples of how to use it for both one-dimensional and multi-dimensional arrays.

The append() function takes two required arguments: the array to which we want to append the new elements and the new elements that we want to append. There is also an optional parameter called the axis, which specifies the axis along which the arrays will be joined.

The default value of axis is None, which means the array is flattened before appending. The documentation provides examples of how to use the append() function with one-dimensional and multi-dimensional arrays:

“` python

import numpy as np

a = np.array([1, 2, 3])

b = np.array([4, 5, 6])

c = np.array([[1, 2, 3], [4, 5, 6]])

# One-dimensional arrays

d = np.append(a, b)

print(d) # Output: [1 2 3 4 5 6]

# Multi-dimensional arrays

e = np.append(c, [[7, 8, 9]], axis=0)

print(e) # Output: [[1 2 3] [4 5 6] [7 8 9]]

f = np.append(c, [[7], [8]], axis=1)

print(f) # Output: [[1 2 3 7] [4 5 6 8]]


By experimenting with these examples, you can familiarize yourself with the append() function and its parameters.

NumPy Concatenate() Documentation

The official NumPy documentation for the concatenate() function can be found at This function combines several arrays into one larger array along a specified axis.

Like the append() function, concatenate() works with one-dimensional and multi-dimensional arrays. The concatenate() function takes a sequence of arrays as its first argument and the axis argument that defaults to 0.

The documentation provides examples of how to use the concatenate() function:

“` python

import numpy as np

a = np.array([[1, 2], [3, 4]])

b = np.array([[5, 6]])

c = np.array([[7], [8]])

# Concatenate without specifying axis

d = np.concatenate((a, b, c))

print(d) # Output: [[1 2] [3 4] [5 6] [7] [8]]

# Concatenate along axis 1

e = np.concatenate((a, b.T), axis=1)

print(e) # Output: [[1 2 5] [3 4 6]]

# Concatenate sequences of arrays

f = np.concatenate((a, b, c), axis=None)

print(f) # Output: [1 2 3 4 5 6 7 8]


The concatenate() function can be used in a variety of ways to achieve different outcomes.


In conclusion, by exploring the official NumPy documentation, you can improve your understanding of the append() and concatenate() functions, helping you write more efficient code. Remember that NumPy arrays have unique properties that require us to use NumPy functions to manipulate them.

As you continue to work with NumPy, familiarizing yourself with the available tools is essential in becoming a proficient programmer. In conclusion, the ‘AttributeError: ‘numpy.ndarray’ object has no attribute ‘append” error is an issue that can occur when attempting to use the append() function on NumPy arrays.

Fortunately, NumPy provides the np.append() function as a solution, which creates a new concatenated array. Additionally, the np.concatenate() function can concatenate multiple arrays into one array.

Using these NumPy functions instead of the append() method can lead to more efficient code. Remember to refer to the official NumPy documentation to increase your understanding of these functions and become a proficient programmer.

Understanding the available tools and functions can help you tackle more complex projects efficiently.