# solve for a*b=c*d in python 2.7
# should work for arbitrary number of variables on each side ie abc=def
 
# user inputs
a = 1
b = 2
c = 7
d = 'solve' # solve for this value
 
lhs = [a,b] # left hand side of eq
rhs = [c,d] # right hand side of eq
 
if 'solve' in lhs:
  value = c*d       # get right hand side
  divide = lhs
elif 'solve' in rhs:
  value = a*b       # get right hand side
  divide = rhs
else:
  raise ValueError('cannot tell which variable to solve for')
 
for num in divide:   # divide by terms on 'solve' side
    if num == 'solve':
      continue # don't divide by 'solve' ... that would be silly
    value = value/float(num)
 
easyCheck = a*b/float(c) # the easy way to do it (less dynamic though)
 
print 'solution is ',value
print 'easy check value is',easyCheck

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