Initial revision

Demo/scripts/fact.py

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+#! /usr/local/python
+
+# Factorize numbers, slowly.
+# This version uses plain integers and is thus limited to 2**31-1.
+
+import sys
+from math import sqrt
+
+error = 'fact.error'		# exception
+
+def fact(n):
+	if n < 1: raise error	# fact() argument should be >= 1
+	if n = 1: return []	# special case
+	res = []
+	# Treat even factors special, so we can use i = i+2 later
+	while n%2 = 0:
+		res.append(2)
+		n = n/2
+	# Try odd numbers up to sqrt(n)
+	limit = int(sqrt(float(n+1)))
+	i = 3
+	while i <= limit:
+		if n%i = 0:
+			res.append(i)
+			n = n/i
+			limit = int(sqrt(float(n+1)))
+		else:
+			i = i+2
+	res.append(n)
+	return res
+
+def main():
+	if len(sys.argv) > 1:
+		for arg in sys.argv[1:]:
+			n = int(eval(arg))
+			print n, fact(n)
+	else:
+		try:
+			while 1:
+				n = int(input())
+				print n, fact(n)
+		except EOFError:
+			pass
+
+main()