How do I sum the total calculated values in a loop (Python 2.7) -

i trying sum total yearly rent period, using code shown below.

any appreciated.

rent_rate = input('please enter price per square foot:')   # price sq/ft lease_rate = input('please enter rate of lease:')           # interest rate lease_term = input('please enter tenor (in years) of lease:')   size_of_space = input('please enter size(in square feet) of space:')    print "year %25s" % "rent rate%25s"  % "rate%25s" % "square feet%25s" % "yearly rent%25s" % "monthly rent"   year in range( 0, lease_term ):    rent_rate = principal * ( 1.0 + rate ) ** year    yearly_rent = rent_rate * size_of_space    monthly_rent = yearly_rent/12    print "%4d%21.2f%21.2f%21.2f%21.2f%21.2f" % ( year + 1, rent_rate, rate, size_of_space, yearly_rent, monthly_rent) 

i think need few things! should assign 'principal' 'rent_rate' because came out of thin air!

also, if user inputs going numbers, should 'int' or 'float' of inputs! here:

rent_rate = float(input('please enter price per square foot:'))    lease_rate = float(input('please enter rate of lease:'))        lease_term = int(input('please enter tenor (in years) of lease:'))   size_of_space = float(input('please enter size(in square feet) of space:'))    print "year %25s" % "rent rate%25s"  % "rate%25s" % "square feet%25s" %  "yearly rent%25s" % "monthly rent"   year in range(0, lease_term):    rent_rate = principal * ( 1.0 + rate ) ** year    yearly_rent = rent_rate * size_of_space    monthly_rent = yearly_rent/12    print "%4d%21.2f%21.2f%21.2f%21.2f%21.2f" % ( year + 1, rent_rate, rate,     size_of_space, yearly_rent, monthly_rent) 

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