I hope I am not being too ignorant :p but here goes... my boss has
written a bit of python code and asked me to speed it up for him...
I've reduced the run time from around 20 minutes to 13 (not bad I think
;) to speed it up further I asked him to replace a loop like this:-
index = 0
for element in a:
av = a[index]
bv = b[index]
cv = c[index]
dv = d[index]
avbv = (av-bv) * (av-bv)
diff = cv - dv
e.append(diff - avbv)
index = index + 1
(where a, b, c and d are 200,000 element float arrays)
to use the built in zip function.. it would seem made for this problem!
for av, bv, cv, dv in zip(a, b, c, d):
avbv = (av-bv) * (av - bv)
diff = cv - dv
e.append(diff - avbv)
however this seems to run much slower than *I* thought it would
(and in fact slower than slicing) I guess what I am asking is.. would
you expect this?
full code listing (I hope I have made a very obvious error):-
import array
import time
a = array.array("f")
b = array.array("f")
c = array.array("f")
d = array.array("f")
e = array.array("f")
for value in xrange(1, 200000, 1):
a.append(float(value))
b.append(float(value))
c.append(float(value))
d.append(float(value))
start = time.time()
index = 0
for element in a:
av = a[index]
bv = b[index]
cv = c[index]
dv = d[index]
avbv = (av-bv) * (av-bv)
diff = cv - dv
e.append(diff - avbv)
index = index + 1
end0 = time.time()
print end0-start
e = array.array("f")
for av, bv, cv, dv in zip(a, b, c, d):
avbv = (av-bv) * (av - bv)
diff = cv - dv
e.append(diff - avbv)
end1 = time.time()
print end1-end0
e = array.array("f")
## just for a laugh my own zip function
## the joke is it runs faster than built in zip ??
def myzip(*args):
index = 0
for elem in args[0]:
zipper = []
for arg in args:
zipper.append(arg[index])
index = index +1
yield zipper
for av, bv, cv, dv in myzip(a, b, c, d):
avbv = (av-bv) * (av - bv)
diff = cv - dv
e.append(diff - avbv)
end2 = time.time()
print end2-end1
timings from 4 million element input array
slice:
8.77999997139
zip():
36.5759999752
myzip():
12.1449999809
--
http://mail.python.org/mailman/listinfo/python-list
