How do I generate PuLP variables and constrains without using exec?

I have written the following Python Code using the PuLP Library for solving the Knapsack Problem using the Integer Programming formulation. I am using strings to generate the LpVariable commands and add the constraints and then executing them with eval. Is there a way to do this without using eval?

from pulp import *

#Knapsack problem

items = input ('Enter the number of items :')

items = int(items)

#print('Enter %d items one by one')

print ('Enter {0} items profit one by one'.format(items))

obj = []
weight = []
knapweight = 0


for i in range(0,items):
    print('Enter {0} item profit : '.format(i+1))
    obj.append(input())

for i in range(0, items):
    print('The profit at {0} is {1}'.format(i, obj[i]))

print ('\nEnter {0} items weights one by one'.format(items))


for i in range(0, items):
    print('Enter {0} item weight'.format(i+1))
    weight.append(input())

for i in range(0, items):
    print('The profit at {0} is {1}'.format(i, weight[i]))

print ('\nEnter the weight of the knapsack :')
knapweight = input()

print ('The weight of the knapsack is : {0}'.format(knapweight))


#generating variables
for i in range(0, items):
    str = 'x{0} = LpVariable("x{1}", cat=\'Binary\')'.format(i+1,i+1)
    print (str)
    exec(str)

prob = LpProblem('Knapsack', LpMaximize)

print ('\nDynamic Generaion\n')

#weight constraint generation
str = "prob += "

for i in range(0, items):
    if i == (items-1):
        str = str + weight[i] + '*x{0}'.format(i+1)
    else:
        str = str + weight[i] + '*x{0}'.format(i+1) + '+'

str = str + '<=' + knapweight
exec(str)
print(str)

#objective function generation
str = "prob += "

for i in range(0, items):
    if i == (items-1):
        str = str + obj[i] + '*x{0}'.format(i+1)
    else:
        str = str + obj[i] + '*x{0}'.format(i+1) + '+'

exec(str)
print(str)

status = prob.solve()
print(LpStatus[status])

print ('\nThe values of the variables : \n')

for i in range(0, items):
    print('x{0} = {1}'.format(i+1, value(eval('x{0}'.format(i+1)))))