You do not "declare" arrays or anything else in python. You simply assign to a (new) variable. If you want a multidimensional array, simply add a new array as an array element.
arr = []
arr.append([])
arr[0].append('aa1')
arr[0].append('aa2')
or
arr = []
arr.append(['aa1', 'aa2'])
GeeksforGeeks
geeksforgeeks.org › python › numpy-append-python
numpy.append() in Python - GeeksforGeeks
April 14, 2025 - When working with multi-dimensional arrays you can specify the axis parameter to control how the values are appended. Python · import numpy as geek arr1 = geek.arange(8).reshape(2, 4) print("2D arr1 :", arr1) print("Shape :", arr1.shape) arr2 = geek.arange(8, 16).reshape(2, 4) print("2D arr2:", arr2) print("Shape :", arr2.shape) arr3 = geek.append(arr1, arr2) print("Appended arr3 by flattened :", arr3) arr3 = geek.append(arr1, arr2, axis = 0) print("Appended arr3 with axis 0 :", arr3) arr3 = geek.append(arr1, arr2, axis = 1) print("Appended arr3 with axis 1 :", arr3) Output : Appending 2D Array ·
Top answer 1 of 12
91
You do not "declare" arrays or anything else in python. You simply assign to a (new) variable. If you want a multidimensional array, simply add a new array as an array element.
arr = []
arr.append([])
arr[0].append('aa1')
arr[0].append('aa2')
or
arr = []
arr.append(['aa1', 'aa2'])
2 of 12
82
There aren't multidimensional arrays as such in Python, what you have is a list containing other lists.
>>> arr = [[]]
>>> len(arr)
1
What you have done is declare a list containing a single list. So arr[0] contains a list but arr[1] is not defined.
You can define a list containing two lists as follows:
arr = [[],[]]
Or to define a longer list you could use:
>>> arr = [[] for _ in range(5)]
>>> arr
[[], [], [], [], []]
What you shouldn't do is this:
arr = [[]] * 3
As this puts the same list in all three places in the container list:
>>> arr[0].append('test')
>>> arr
[['test'], ['test'], ['test']]
do you guys know how to add append an array in a 2d array?
Easy way: x = your_list[0] for i in range(len(5)): your_list.append(x) Might be a more optimized way to do it but at least it should work More on reddit.com
5
5
February 19, 2024Using numpy.append() without losing array dimensions? [Mac, 2.7]
By default numpy.append flattens both arrays. I would use numpy.dstack and just stack all the arrays on top of one another. You will get a size of (101,6,i) where i is the ith array stacked. import numpy as np a = np.arange(9).reshape(3,3) b = np.arange(9,18).reshape(3,3) c = np.arange(18,27).reshape(3,3) d = np.arange(27,36).reshape(3,3) final = np.dstack((a, b, c, d)) print final.shape print np.array_equal(final[:,:,0], a) print np.array_equal(final[:,:,1], b) print np.array_equal(final[:,:,2], c) print np.array_equal(final[:,:,3], d) The other option is to initialize final_arr to be the correct size first. Then you just index the new arrays into their proper positions. More on reddit.com
6
2
February 5, 2014How to append 3d numpy array to a 4d array
Sounds like what you really need is a python list of 3D numpy arrays. Appending to a numpy array is possible with np.append or np.concat, but it's very expensive because it forces the entire array to be remade. Is there any reason you want a 4D array?
More on reddit.com 8
1
March 9, 20192D array ( list ) in Python
https://www.reddit.com/r/learnpython/wiki/faq#wiki_why_is_my_list_of_lists_behaving_strangely.3F
More on reddit.com 4
1
February 27, 2018Videos
GeeksforGeeks
geeksforgeeks.org › python › appending-to-2d-list-in-python
Appending to 2D List in Python - GeeksforGeeks
July 23, 2025 - += operator allows you to extend a sublist with multiple elements in a concise manner. ... This is equivalent to using extend(). If we want to append multiple sublists dynamically list comprehension is a concise option.
W3Schools
w3schools.com › python › numpy › numpy_array_join.asp
NumPy Joining Array
HTML CSS JAVASCRIPT SQL PYTHON JAVA PHP HOW TO W3.CSS C C++ C# BOOTSTRAP REACT MYSQL JQUERY EXCEL XML DJANGO NUMPY PANDAS NODEJS DSA TYPESCRIPT ANGULAR ANGULARJS GIT POSTGRESQL MONGODB ASP AI R GO KOTLIN SWIFT SASS VUE GEN AI SCIPY AWS CYBERSECURITY DATA SCIENCE INTRO TO PROGRAMMING INTRO TO HTML & CSS BASH RUST · NumPy HOME NumPy Intro NumPy Getting Started NumPy Creating Arrays NumPy Array Indexing NumPy Array Slicing NumPy Data Types NumPy Copy vs View NumPy Array Shape NumPy Array Reshape NumPy Array Iterating NumPy Array Join NumPy Array Split NumPy Array Search NumPy Array Sort NumPy Array Filter
Reddit
reddit.com › r/learnpython › do you guys know how to add append an array in a 2d array?
r/learnpython on Reddit: do you guys know how to add append an array in a 2d array?
February 19, 2024 -
say i have array [[1,2,3,4,5]], how can i duplicate it 5 times to [[1,2,3,4,5],[1,2,3,4,5],[1,2,3,4,5],[1,2,3,4,5],[1,2,3,4,5]] ?
Top answer 1 of 4
1
Easy way: x = your_list[0] for i in range(len(5)): your_list.append(x) Might be a more optimized way to do it but at least it should work
2 of 4
1
y=x*5 will give you a pointer to the same OG list. It’s generally not what you want, but if you’re going to numpy, it’s fine. Otherwise, why not x.append([1,2,3,4,5]) and stick it in a for loop. You seem like you know, but are looking for a slick way to do it and there really isn’t.
Python documentation
docs.python.org › 3 › tutorial › datastructures.html
5. Data Structures — Python 3.14.3 documentation
The list methods make it very easy to use a list as a stack, where the last element added is the first element retrieved (“last-in, first-out”). To add an item to the top of the stack, use append(). To retrieve an item from the top of the ...
Python Forum
python-forum.io › thread-16863.html
2D arrays and appending values using a loop
Hi, I need some help with the appending of the values into the 2D array using a FOR loop. I am ok with printing the values, its the append that I need help with: Array=[[100,20],[90,29],[102,89],[2,2]] for row in Array: print ('Row Values:',...
Vultr Docs
docs.vultr.com › python › third-party › numpy › append
Python Numpy append() - Add Elements to Array | Vultr Docs
April 10, 2025 - Here, python append to numpy array is done efficiently by appending elements to a list first, then converting it to a NumPy array in one step.
DigitalOcean
digitalocean.com › community › tutorials › python-add-to-array
Python Array Add: How to Append, Extend & Insert Elements | DigitalOcean
April 15, 2025 - Learn how to add elements to an array in Python using append(), extend(), insert(), and NumPy functions. Compare performance and avoid common errors.
Medium
medium.com › @whyamit101 › how-to-append-two-arrays-in-numpy-efa74e5e2788
How to Append Two Arrays in NumPy? | by why amit | Medium
February 26, 2025 - Since we didn’t specify an axis, NumPy flattens everything into a single array. Example 1: Appending Without axis (Flattens Everything) Let’s see what happens when we append 2D arrays without an axis.
Snakify
snakify.org › two-dimensional lists (arrays)
Two-dimensional lists (arrays) - Learn Python 3 - Snakify
Another (but similar) way: create an empty list and then append a new element to it n times (this element should be a list of length m): ... But the easiest way is to use generator, creating a list of n elements, each of which is a list of m zeros: ... In this case each element is created independently from the others. The list [0] * m is n times consructed as the new one, and no copying of references occurs. Say, a program takes on input two-dimensional array in the form of n rows, each of which contains m numbers separated by spaces.
Spark By {Examples}
sparkbyexamples.com › home › python › how to append numpy arrays examples
How to Append NumPy Arrays Examples - Python
March 27, 2024 - In code, two 2D NumPy arrays are created, and then a new row [5, 7, 9] is appended to the original array using np.append() along axis=0.
NumPy
numpy.org › doc › 2.2 › reference › generated › numpy.append.html
numpy.append — NumPy v2.2 Manual
Delete elements from an array. ... >>> import numpy as np >>> np.append([1, 2, 3], [[4, 5, 6], [7, 8, 9]]) array([1, 2, 3, ..., 7, 8, 9])
Note.nkmk.me
note.nkmk.me › home › python › numpy
NumPy: append() to add values to an array | note.nkmk.me
February 4, 2024 - By default, when the first argument is a two-dimensional array, it is flattened to one dimension, and then the values from the second argument are appended to it. a_2d = np.arange(6).reshape(2, 3) print(a_2d) # [[0 1 2] # [3 4 5]] ...
AskPython
askpython.com › home › two dimensional array in python
Two Dimensional Array in Python - AskPython
August 6, 2022 - size = int(input()) array_input ... ... Elements in a 2D array can be inserted using the insert() function specifying the index/position of the element to be inserted....
DataCamp
datacamp.com › doc › numpy › append
NumPy append()
NumPy's `append()` function is used to add elements to the end of an existing array, effectively creating a new array with the additional elements.
iO Flood
ioflood.com › blog › numpy-append
Numpy Append Function: From Basics to Advanced Usage
January 31, 2024 - In Numpy, the ‘axis’ parameter refers to the dimension of the array. For a 1D array, there’s only one axis (axis=0). For a 2D array, there are two axes: axis=0 (rows) and axis=1 (columns). When you use the ‘numpy.append()’ function, the ‘axis’ parameter defines along which axis the arrays will be appended.
Delft Stack
delftstack.com › home › howto › python › append 2d array python
How to Append 2D Array in Python | Delft Stack
February 22, 2025 - Python’s built-in lists can represent 2D arrays as lists of lists. The simplest way to append values is using the append() method.
EyeHunts
tutorial.eyehunts.com › home › python 2d array append
Python 2D array append
June 27, 2023 - # Initialize a 2D array array_2d = [[1, 2, 3], [4, 5, 6]] # Append a new row to the 2D array new_row = [7, 8, 9] array_2d.append(new_row) # Append elements to an existing row in the 2D array existing_row_index = 1 array_2d[existing_row_index].append(7) array_2d[existing_row_index].append(8) # Print the modified 2D array for row in array_2d: print(row)
Scaler
scaler.com › home › topics › 2d array in python
2D Array in Python | Python Two-Dimensional Array - Scaler Topics
October 10, 2025 - Inserting a value in an array means adding a new element at a given index in the array and then shifting the remaining elements accordingly. Inserting a value would cause the values after to be shifted forward. We can add values in a python 2D array in two ways:-