The script below will unroll 1048576 (20-bits) x 32-bytes (32-megabytes) of SHA256 hash digests into memory and will perform 1048576 (20-bits) of array index look ups to get the final hash digest.

import hashlib
def tohex(h):
	o = ""
	for c in h:
		d = ord(c)
		f = ""
		if (d < 16):
			f = "0"
		d = hex(d)
		o += (f + d[2:])
	return o
def scrypt(p, r, m):
	h = hashlib.sha256(p).digest()
	#print(tohex(h))
	k = h
	l = []
	s = 0
	while (s < m):
		k = hashlib.sha256(k).digest()
		#print(s,tohex(k))
		l.append(k)
		s += 1
	k = h
	i = 0
	n = (m - 1)
	while (i < r):
		tt = ((ord(k[28]) << 24) | (ord(k[29]) << 16) | (ord(k[30]) << 8) | (ord(k[31]) << 0))
		j = (tt & n)
		#print(i,hex(tt),j,tohex(l[j]))
		k = l[j]
		i += 1
	return tohex(k)
s = scrypt("P@ssW0rd1!", 2**20, 2**20)
print(s)

cat /proc/cpuinfo | grep -i 'model.*name' | head -n 1 ; date ; python scrypt.py ; date
model name	: Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz
Sat Jan 25 13:20:42 EST 2014
3f26b65f9c3ae151c7113efd3abe57a5e7257ba9b9010ec53acde03112b5a9b1
Sat Jan 25 13:20:44 EST 2014

# cat /proc/cpuinfo | grep -i 'model.*name' | head -n 1 ; date ; python scrypt.py ; date
model name	: Intel(R) Xeon(R) CPU E5-2650 0 @ 2.00GHz
Sun Jan 26 19:18:13 UTC 2014
3f26b65f9c3ae151c7113efd3abe57a5e7257ba9b9010ec53acde03112b5a9b1
Sun Jan 26 19:18:16 UTC 2014

sysctl -n machdep.cpu.brand_string ; date ; python scrypt.py ; date
Intel(R) Core(TM) i5-3210M CPU @ 2.50GHz
Sat 25 Jan 2014 13:16:15 EST
3f26b65f9c3ae151c7113efd3abe57a5e7257ba9b9010ec53acde03112b5a9b1
Sat 25 Jan 2014 13:16:19 EST

and also, a random py script to generate random passwords:

import os
import random
import string
import sys
f = open(sys.argv[1], "r")
for l in f.readlines():
	l = l.strip()
	p = []
	for x in range(0, int(sys.argv[2])):
		if ((x % 4) == 0):
			p.append(random.choice(string.digits))
		elif ((x % 4) == 1):
			p.append(random.choice(string.uppercase))
		elif ((x % 4) == 2):
			p.append(random.choice(string.lowercase))
		elif ((x % 4) == 3):
			p.append(random.choice("~!@#$%^&*+"))
	random.shuffle(p)
	s = "".join(p)
	print(l + "," + s)
f.close()