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 10, 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
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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:-