Arrays

Notes on arrays and array-like structures.

Questions

Goodrich Python Questions

See also Arrays/Python

exploring relationship between list length and size

Question 5-1: execute the code fragment, and compare the results to those in the book.

The code fragment starts with an empty list, dynamically growing the list by appending items to the end, and showing how the size of the list is doubled each time the list gets bigger.

This also demonstrates the importance of declaring a list size if you know it! It's really expensive to keep resizing a list. (Remember the days of Matlab - you'd get an order of magnitude savings in time simply by declaring the array straight out.

Key function:

• sys.getsizeof(data) to get the size of a list in bytes

The code populates the list with None (null) objects, which take up as much space as pointers to addresses in memory (64 bits on a 64 bit memory/computer)

import sys
data = []
n = 50
for k in range(n+1):
    a = len(data)
    b = sys.getsizeof(data)
    print("Length: {0:3d}\tSize in bytes: {1:6d}".format(a,b))
    data.append(None)

import sys

<pre>
$ python list_length_sizeof.py
Length:   0	Size in bytes:     72
Length:   1	Size in bytes:    104
Length:   2	Size in bytes:    104
Length:   3	Size in bytes:    104
Length:   4	Size in bytes:    104
Length:   5	Size in bytes:    136
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Length:   9	Size in bytes:    200
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