Oct 3, 2009 · @AndersonGreen As I said there's no such thing as a variable declaration in Python. You would create a multidimensional list by taking an empty list and putting other lists inside it or, if the dimensions of the list are known at write-time, you could just write it as a literal like this: my_2x2_list = [[a, b], [c, d]].

Edit: If you don't know the size of big_array in advance, it's generally best to first build a Python list using append, and when you have everything collected in the list, convert this list to a numpy array using numpy.array(mylist). The reason for this is that lists are meant to grow very efficiently and quickly, whereas numpy.concatenate ...

One thing to note: all elements in the list will have initially the same id (or memory address). When you change any element later on in the code, this will impact only the specified value, - HOWEVER - if you create a list of custom objects in this way (using the int multiplier) and later on you change any property of the custom object, this will change ALL the objects in the list.

Dec 7, 2009 · Use the array module. With it you can store collections of the same type efficiently. >>> import array >>> import itertools >>> a = array_of_signed_ints = array.array("i", itertools.repeat(0, 10)) For more information - e.g. different types, look at the documentation of the array module. For up to 1 million entries this should feel pretty snappy.

The question says "How to declare array of zeros ..." but then the sample code references the Python list: buckets = [] # this is a list However, if someone is actually wanting to initialize an array, I suggest: from array import array my_arr = array('I', [0] * count) The Python purist might claim this is not pythonic and suggest:

As @Arnab and @Mike pointed out, an array is not a list. Few differences are 1) arrays are fixed size during initialization 2) arrays normally support lesser operations than a list. Maybe an overkill in most cases, but here is a basic 2d array implementation that leverages hardware array implementation using python ctypes(c libraries)

To create an empty multidimensional array in NumPy (e.g. a 2D array m*n to store your matrix), in case you don't know m how many rows you will append and don't care about the computational cost Stephen Simmons mentioned (namely re-buildinging the array at each append), you can squeeze to 0 the dimension to which you want to append to: X = np.empty(shape=[0, n]).

Jul 12, 2011 · Matrix operations in numpy most often use an array type with two dimensions. There are many ways to create a new array; one of the most useful is the zeros function, which takes a shape parameter and returns an array of the …

May 5, 2011 · I need to create a NumPy array of length n, each element of which is v. Is there anything better than: a = empty(n) for i in range(n): a[i] = v I know zeros and ones would work for v = 0, 1. I

Aug 27, 2014 · There isn't a way to implicitly call an Object() constructor for each element of an array like there is in C++ (recall that in Java, each element of a new array is initialised to null for reference types). I would say that your list comprehension method is the most Pythonic: lst = [Object() for i in range(100)]