How to Declare an Array in Python

How to declare an array in python

As noted in the comments, initializing a list (not an array, that's not the type in Python, though there is an array module for more specialized use) to a bunch of zeroes is just:

a = [0] * 10000

If you want an equivalent to memset for this purpose, say, you want to zero the first 1000 elements of an existing list, you'd use slice assignment:

a[:1000] = [0] * 1000

How to declare arrays in python3

Based on your last line (that you don't know how many elements are there in the array), you want to create an empty array and then use the append() function to add values into it.

The modified version of the code which you have provided in the question:

ip_pb = []
ip_pb.append("0111111100000000000000011110001")
print(ip_pb)

How to declare and add items to an array in Python?

{} represents an empty dictionary, not an array/list. For lists or arrays, you need [].

To initialize an empty list do this:

my_list = []

or

my_list = list()

To add elements to the list, use append

my_list.append(12)

To extend the list to include the elements from another list use extend

my_list.extend([1,2,3,4])
my_list
--> [12,1,2,3,4]

To remove an element from a list use remove

my_list.remove(2)

Dictionaries represent a collection of key/value pairs also known as an associative array or a map.

To initialize an empty dictionary use {} or dict()

Dictionaries have keys and values

my_dict = {'key':'value', 'another_key' : 0}

To extend a dictionary with the contents of another dictionary you may use the update method

my_dict.update({'third_key' : 1})

To remove a value from a dictionary

del my_dict['key']

How to define a two-dimensional array?

You're technically trying to index an uninitialized array. You have to first initialize the outer list with lists before adding items; Python calls this
"list comprehension".

# Creates a list containing 5 lists, each of 8 items, all set to 0
w, h = 8, 5
Matrix = [[0 for x in range(w)] for y in range(h)] 

#You can now add items to the list:

Matrix[0][0] = 1
Matrix[6][0] = 3 # error! range... 
Matrix[0][6] = 3 # valid

Note that the matrix is "y" address major, in other words, the "y index" comes before the "x index".

print Matrix[0][0] # prints 1
x, y = 0, 6 
print Matrix[x][y] # prints 3; be careful with indexing! 

Although you can name them as you wish, I look at it this way to avoid some confusion that could arise with the indexing, if you use "x" for both the inner and outer lists, and want a non-square Matrix.

How work to with an array of arrays and how initialize multiple arrays in Numpy?

List of Arrays

You can create a list of arrays:

agents = [np.array([]) for _ in range(50)]

And then to append values to some agent, say agents[0], use:

items_to_append = [1, 2, 3]  # Or whatever you want.
agents[0] = np.append(agents[0], items_to_append)

List of Lists

Alternatively, if you don't need to use np.arrays, you can use lists for the agents values. In that case you would initialize with:

a = [[] for _ in range(50)]

And you can append to agents[0] with either

single_value = 1  # Or whatever you want.
agents[0].append(single_value)

Or with

items_to_append = [1, 2, 3]  # Or whatever you want
agents[0] += items_to_append

Python how to declare dynamic ( number of arrays )

While you can technically do this in python using exec, it is not recommended.

Instead, you should create a list of lists:

arrays = [[] for _ in range(int(input())]

Or a dictionary of lists:

arrays = {f'arr{i}': [] for i in range(int(input())}

How to declare array of zeros in python (or an array of a certain size)

buckets = [0] * 100

Careful - this technique doesn't generalize to multidimensional arrays or lists of lists. Which leads to the List of lists changes reflected across sublists unexpectedly problem

Creating an array of arrays dynamically in Python

You should not use the same x array in every loop but create it from scratch:

rows = 10
cols = 3
arr = []
for i in range(rows):
    x = []
    for j in range(cols):
        x.append((i + 1) ** j)
    arr.append(x)
print(arr)

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