Happy Numbers done

Numbers/happy_numbers.py

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+"""
+Happy Numbers - A happy number is defined by the
+following process. Starting with any positive integer,
+replace the number by the sum of the squares of its
+digits, and repeat the process until the number equals
+1 (where it will stay), or it loops endlessly in a
+cycle which does not include 1. Those numbers for which
+this process ends in 1 are happy numbers, while those
+that do not end in 1 are unhappy numbers. Take an input
+number from user, and find first 8 happy numbers from
+that input.
+"""
+
+NUMBERS_REQUIRED = 8 # number of happy numbers required
+
+def is_happy_number(num):
+    seen = []
+    while True:
+        sum_digits = sum(int(digit) ** 2 for digit in str(num))
+        if sum_digits == 1:
+            return True
+        elif sum_digits in seen:
+            return False
+        else:
+            num = sum_digits
+            seen.append(num)
+
+if __name__ == '__main__':
+
+    happies = [] # list of happy numbers found
+
+    num = input('Start at: ')
+
+    while len(happies) != NUMBERS_REQUIRED:
+        if is_happy_number(num):
+            happies.append(num)
+        num += 1
+
+    print happies
+