First post and first code. Primefinder

The first post on this blog. I have previously used math packages, namely MATLAB, to solve chemical engineering problems. In an attempt to move away from commercial products and gain a better understanding of what is going on behind the curtain; I've decided to learn how to use python to solve these problems. I'm posting the code as I'm learning. In the beginning it will be mostly python examples but I hope I soon can get in to solve real problems.

This code example generates all prime numbers within a given range. It is a good python example with uses: if statements, for loops, while loops, and user inputs. I know the code can be optimized but I leave it to you. The code is licensed under GNU GPLv3.

Copy the code and save it to a file named primefinder.py and run.

The Code:

#!/usr/bin/env python

print 'This program finds all prime numbers between a range given'
nMin = eval(raw_input('Enter left hand side of the range: '))
nMax = eval(raw_input('Enter right hand side, number is excluded: '))

# Checking if nMin is to small for this algorithm
if nMin <= 2: # If less than 2, add to and start with 3
 a = [2] 
 print '2' 
 nMin = 3
else:
 a = []

i = 2
# Loop to find all primes in the range
for n in range(nMin,nMax):
 while i < n:   # For every number less than n:
  if n%i != 0:  # If n is not a factor of i
   prime = 1 # Set the checking variable to true
   i = i +1  # Go to next number
  else: 
   prime = 0 # Otherwise set checking variable to false
   i = n + 1 # Exit the loop
 i = 2     # Reset i for next number in the range
 # Print the primes found and save them in variable a 
 if prime == 1:
  print n 
  a.append(n)

# Find out how many was found and print result
Size = len(a)
print 'The number of prime numbers found in this range is', Size

# Ask user what to do next.
while 1>0:
 print 'Would you like me to reprint all the numbers?'
 ANS = raw_input('yes/no: ')
 if ANS == 'yes':
  print a
  exit()
 elif ANS == 'no':
  exit()
 else:
  print 'Type yes or no'

An example of the code running:

This program finds all prime numbers between a range given
Enter left hand side of the range: 0
Enter right hand side, number is excluded: 50
2
3
5
7
11
13
17
19
23
29
31
37
41
43
47
The number of prime numbers found in this range is 15
Would you like me to reprint all the numbers?
yes/no: yes
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]