> Frank Millman <fr***@chagford.com> wrote:
This is a question about the performance trade-off between two methods
of storing data. One method is to create a separate attribute for each
piece of data, and get/set the value according to its name. Another
method is to create a list, and get/set the value according to its
position in the list. In my limited tests, the first method is quicker.
Aahz <aa**@pythoncraft.com> wrote:
That doesn't make any sense. While lists and dicts are both essentially
O(1) for access, the constant is larger for dicts. Please show us your
testing code.
Code shown below, but here is a summary -
print f.getval_from_attr()
print f.getval_from_list()
print f.setval_in_attr(1000)
print f.setval_in_list(1000)
Results, to 2 decimal places, are as follows -
0.32
0.45
0.34
0.44
OTOH, there's certainly nothing wrong with using dicts; they are the
single most fundamental Python data type after strings. (All Python
name/attribute access is built on top of dicts.)
This is exactly my point, but I may be misunderstanding how it works
internally. If I have a class with 20 attributes, it will have a
dictionary with 20 entries. If I have hundreds of instances of the
class, do I end up with hundreds of dictionaries (or the equivalent
internal structures), and if so, does this not lead to memory bloat?
If I store the data in a list, there will only be one dictionary entry
per instance. On the other hand, I suppose there must be some
reference to each of the elements of each list, so maybe there is an
equivalent overhead. Is this a valid concern, or am I worrying about
nothing?
Thanks for your input. Test program is shown below.
Frank
-------------------------------------
from time import time
class frank:
def __init__(self,a,b,c,l):
self.a = a # an attribute
self.b = b # an attribute
self.c = c # an attribute
self.l = l # a list
def getval_from_attr(self):
start = time()
for i in xrange(1000000):
aa = self.a
return (time() - start)
def getval_from_list(self):
start = time()
for i in xrange(1000000):
aa = self.l[0]
return (time() - start)
def setval_in_attr(self,val):
start = time()
for i in xrange(1000000):
self.a = val
return (time() - start)
def setval_in_list(self,val):
start = time()
for i in xrange(1000000):
self.l[0] = val
return (time() - start)
f = frank(100,200,300,[100,200,300])
print f.getval_from_attr()
print f.getval_from_list()
print f.setval_in_attr(1000)
print f.setval_in_list(1000)
-------------------------------------
Results, to 2 decimal places, are as follows -
0.32
0.45
0.34
0.44
