Pascal coordinate calculator

Hard Challenges/8PascalCoordinates.py

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+#Write a program that will take coordinates, and tell you the corresponding number in pascals triangle. For example:
+#Input: 1, 1
+#output:1
+#=======
+#input: 4, 2
+#output: 6
+#=======
+#input: 1, 19
+#output: error/nonexistent/whatever
+import re 
+
+def factorial(n):
+	if n == 0:
+		return 1
+	else:
+		fac = 1
+		for i in xrange(1,n+1):
+			fac*=i
+	return fac
+
+#If it is row 4, column 2, we want 4 choose 2
+#The formula for this combination is (row!)/((row!)*(row-column)!)
+#Also, remember that the first row/column in the triangle is row/column 0, not 1
+
+def prompt():
+	print "Hello, this will give you the number of a coordinate in pascals triangle"
+	coordinates = raw_input("Enter the coordinates as follows (row, column) ")
+	coordinates = re.findall('\d+', coordinates)
+	return coordinates
+
+def calculate_number(coordinates):
+	row = int(coordinates[0])
+	column = int(coordinates[1])
+	pascals_number = (factorial(row)/((factorial(column))*factorial(row-column)))
+	if pascals_number < 1:
+		return -1
+	return pascals_number
+
+def main():
+	coords = prompt()
+	number = calculate_number(coords)
+	if number > 0:
+		print number
+	else:
+		print "Non-existant"
+
+if __name__ == '__main__':
+	main()