How to define a dynamic two-dimensional array in python?

Question

I want to define a dynamic two-dimensional array in python.

I don't know how many rows my two-dimensional array will have at the start of my program. I would like to define new rows in this 2D array as needed.

As like this code:

array = [][100]
array[0][]  = new array()
array[0][2] = 'hello'

array[1][] = new array()
array[1][3]= 'hello'

There are no real two-dimensional arrays in Python, but you can have a list of lists. And you don't need to specify the size beforehand. Or are you really talking about Python arrays ? — Felix Kling
– Felix Kling, Commented Jul 13, 2011 at 1:00
Yes , I want to define Python arrays.Give Me example how to define list of list whit out specify the size beforehand. thanks — Masoud Abasian
– Masoud Abasian, Commented Jul 13, 2011 at 1:03
i want to do this: >>> mat =[][] >>> mat[0] = ['row1','row1','row1'] >>> mat[1] = ['row2','row2'] >>> mat[2]=['row3'] and give value like this: >>> print mat[1][1] row2 — Masoud Abasian
– Masoud Abasian, Commented Jul 13, 2011 at 1:28
I suggest you read a Python tutorial first (docs.python.org/tutorial). Understanding the basic data types is essential. — Felix Kling
– Felix Kling, Commented Jul 13, 2011 at 7:34

Eryk Sun · Accepted Answer · 2011-07-13 05:52:00Z

Do you mean something like the following?

class DynamicList(list):

    def __getslice__(self, i, j):
        return self.__getitem__(slice(i, j))
    def __setslice__(self, i, j, seq):
        return self.__setitem__(slice(i, j), seq)
    def __delslice__(self, i, j):
        return self.__delitem__(slice(i, j))

    def _resize(self, index):
        n = len(self)
        if isinstance(index, slice):
            m = max(abs(index.start), abs(index.stop))
        else:
            m = index + 1
        if m > n:
            self.extend([self.__class__() for i in range(m - n)])

    def __getitem__(self, index):
        self._resize(index)
        return list.__getitem__(self, index)

    def __setitem__(self, index, item):
        self._resize(index)
        if isinstance(item, list):
            item = self.__class__(item)
        list.__setitem__(self, index, item)

>>> mat = DynamicList()
>>> mat[0] = ['row1','row1','row1']
>>> mat[1] = ['row2','row2']
>>> mat[2]= ['row3']
>>> mat
[['row1', 'row1', 'row1'], ['row2', 'row2'], ['row3']]
>>> print mat[1][1]
row2
>>> mat[5][5] = 'row5'
>>> mat
[['row1', 'row1', 'row1'], ['row2', 'row2'], ['row3'], [], [], [[], [], [], [], 
[], 'row5']]
>>> print mat[5]
[[], [], [], [], [], 'row5']
>>> print mat[5][5]
row5

John Zwinck · Accepted Answer · 2011-07-13 01:30:29Z

4

How about using NumPy's matrix class?

answered Jul 13, 2011 at 1:30

John Zwinck

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