Using bisect for linear interpolation

bisect.py

#!/usr/bin/env python
# encoding: utf-8

from bisect import bisect
	
# Roark's Table 26, Case 10, with three edges fixed
# a / b, and b1 are defined as lists below:
a_by_b = [0.25, 0.50, 0.75, 1.00, 1.50, 2.00, 3.00]
b1 = [0.020, 0.081, 0.173, 0.321, 0.727, 1.226, 2.105]

a, b = input("Enter a, b: ")
abyb = float(a) / b

try:
    i = a_by_b.index(abyb)
    beta1 = b1[i]

except ValueError:
# a/b did not match any value in a_by_b
    i = bisect(a_by_b, abyb)
    j = i - 1
    P = b1[i] - b1[j] 
    q = (abyb - a_by_b[j])
    Q = (a_by_b[i] - a_by_b[j])
	beta1 =  b1[j] + (P * q / Q)

finally:
    print "a/b               : ", round(abyb, 2)
    print "Index of a/b ratio: ", i
    print "beta1             : ", beta1

pass