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 › 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.
Delft Stack
delftstack.com › "delft stack" › "howto" › "python how-to's" › "how to append 2d array in 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.
Two dimensional array in python - Stack Overflow
What you're using here are not arrays, but lists (of lists). If you want multidimensional arrays in Python, you can use Numpy arrays. You'd need to know the shape in advance. ... You try to append to second element in array, but it does not exist. More on stackoverflow.com
Appending to 2D lists in Python - Stack Overflow
this is the most bizarre functionality ... in Python. seems almost like a bug. 2021-11-22T22:26:19.01Z+00:00 ... Save this answer. ... Show activity on this post. ... In other words, all three list references refer to the same list instance. ... Save this answer. ... Show activity on this post. Came here to see how to append an item to a 2D array, but the title ... More on stackoverflow.com
#12 how am I suppose to add to the 2d list?
You must select a tag to post in this category. Please find the tag relating to the section of the course you are on E.g. loops, learn-compatibility When you ask a question, don’t forget to include a link to the exercise or project you’re dealing with! If you want to have the best chances ... More on discuss.codecademy.com
0
0
April 11, 2023python - How to use append for 2D arrays? - Stack Overflow
You can check the difference in ... that np.append uses np.concatenate 2019-02-25T08:18:35.197Z+00:00 ... K.Maj your answer does not answer the question. The question was about: Why x does not change the value? 2019-02-25T11:03:50.27Z+00:00 ... Thanks. But it seems it changes x from a 2D array to 1D ... More on stackoverflow.com
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
my_list = [[1, 2, 3, 4, 5]] new_list = my_list * 5 print(new_list) Prints: [[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]] But be aware that this only creates multiple labels to the same [1, 2, 3, 4, 5] list object. Mutating any one of the inner lists mutates all of the inner lists as there is only one inner list object: new_list[0][0] += 40 print(new_list) print(my_list) # The original list object Prints: [[41, 2, 3, 4, 5], [41, 2, 3, 4, 5], [41, 2, 3, 4, 5], [41, 2, 3, 4, 5], [41, 2, 3, 4, 5]] [[41, 2, 3, 4, 5]] but you can reassign different objects within new_list: new_list[1] = [7,8,9] print(new_list) Prints: [[41, 2, 3, 4, 5], [7, 8, 9], [41, 2, 3, 4, 5], [41, 2, 3, 4, 5], [41, 2, 3, 4, 5]] If you actually want deep copies of the original inner list, you can use a list comprehension: my_list = [[1, 2, 3, 4, 5]] new_list = [my_list[0][:] for _ in range(5)] new_list[0][0] += 40 print(new_list) Prints: [[41, 2, 3, 4, 5], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5]]
2 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
how would you instantiate a two-dimensional array in the constructor? Nov 21, 2021
r/learnpython 4y ago
First time working with classes. How do I append an object to a list and how do I find a specific value in each object in the list? Nov 1, 2023
r/learnpython 2y ago
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']]
Kite
kite.com › python › answers › how-to-append-to-a-2d-list-in-python
Kite.com
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Top answer 1 of 3
72
You haven't created three different empty lists. You've created one empty list, and then created a new list with three references to that same empty list. To fix the problem use this code instead:
listy = [[] for i in range(3)]
Running your example code now gives the result you probably expected:
>>> listy = [[] for i in range(3)]
>>> listy[1] = [1,2]
>>> listy
[[], [1, 2], []]
>>> listy[1].append(3)
>>> listy
[[], [1, 2, 3], []]
>>> listy[2].append(1)
>>> listy
[[], [1, 2, 3], [1]]
2 of 3
19
[[]]*3 is not the same as [[], [], []].
It's as if you'd said
a = []
listy = [a, a, a]
In other words, all three list references refer to the same list instance.
IQCode
iqcode.com › code › python › python-2d-array-append
python 2d array append Code Example
temp_list = [[], [], [], []] temp_list[0].append("a1") temp_list[1].append("a2") temp_list[2].append("a3") tem...
AdamSmith.haus
adamsmith.haus › python › answers › how-to-append-to-a-2d-list-in-python
How to append to a 2D list in Python - Adam Smith
Python answers, examples, and documentation
EyeHunts
tutorial.eyehunts.com › home › python 2d array append
Python 2D array append
June 27, 2023 - To append elements to a 2D array in Python, you can use the append() method available for Python lists. Here's the syntax for appending...
Statistics Globe
statisticsglobe.com › home › python programming language for statistics & data science › append to 2d list in python (3 examples)
Extend 2D List in Python (3 Examples) | Append New Elements
April 5, 2023 - How to add a new element to a 2D list in Python - Create demo 2D list - Add new element to 2D list using append() method
Dot Net Perls
dotnetperls.com › 2d-python
Python - 2D List Examples - Dot Net Perls
Step 2 We access each sub-list and call append on it. This appends to the inner lists. Step 3 We display the element at indexes 0, 0 and this value is 1. With the print() method we can display the entire list contents. Step 4 This loop can iterate rows and columns in the 2D list.
Iditect
iditect.com › faq › python › appending-to-2d-lists-in-python.html
Appending to 2D lists in Python
In Python, you can append elements to a 2D list (a list of lists) using the append() method or list comprehension. A 2D list is essentially a list where each element is itself a list.
AskPython
askpython.com › python › 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....
Python Forum
python-forum.io › thread-30401.html
Append 2d empty lists
October 19, 2020 - Hi there! I wanted to store my functions result in a 2d list. The function returns 5 values and has to run 100 times in a for loop. I tried to initiate a storage list by ding this: list1 = [[]]*5which returns list1 = [[], [], [], [], []] However, w...
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.
Codecademy Forums
discuss.codecademy.com › computer science
#12 how am I suppose to add to the 2d list? - Computer Science - Codecademy Forums
April 11, 2023 - You must select a tag to post in this category. Please find the tag relating to the section of the course you are on E.g. loops, learn-compatibility When you ask a question, don’t forget to include a link to the exercise or project you’re dealing with! If you want to have the best chances ...
Sololearn
sololearn.com › en › Discuss › 2630146 › runtime-of-appending-items-from-a-2d-array-to-a-1d-list
Runtime of appending items from a 2d array to a 1d list | Sololearn: Learn to code for FREE!
If n is the size of the original un-flattened list (5), Then I would say its O(n) + O(n*m log n*m), but this might just be a bit much for me to wrap my head around atm. Lol ... Thank you. It would be something like this: def flat_matrix(A): flat = [] for i in range(len(A)): for j in range(len(A[i])): flat.append(A[i][j]) return flat
NumPy
numpy.org › doc › stable › reference › generated › numpy.append.html
numpy.append — NumPy v2.5 Manual
Delete elements from an array. ... Try it in your browser! >>> import numpy as np >>> np.append([1, 2, 3], [[4, 5, 6], [7, 8, 9]]) array([1, 2, 3, ..., 7, 8, 9])
Top answer 1 of 4
8
You're forgetting to append the empty list beforehand. Thus why you get a, IndexError when you try to do arr[i].
arr = []
for i in range(10):
arr.append([])
for j in range(5):
arr[i].append(i*j)
2 of 4
7
You need to define your initial array in the following way: arr=[[] for i in range(10)], as you cannot append a value to a nonexistent array (which is what happens when i>=1). So the code should look like:
arr=[[] for i in range(10)]
for i in range(10):
for j in range(5):
arr[i].append(i*j)
print(i,i*j)
print(arr)