Speed improvements for prime finder - especially for large ranges

Author: kylesalk

Prime/code.py

@@ -1,46 +1,40 @@
 def SieveOfEratosthenes(range_to):
 
-  # creating a boolean array first
-  prime = [True for i in range(range_to + 1)]
-  p = 2
-  while (p * p <= range_to):
-       
-    # If prime[p] is not changed, then it is a prime
-    if (prime[p] == True):
-         
-        # Update all multiples of p
-        for i in range(p * 2, range_to + 1, p):
-            prime[i] = False
-    p += 1
-  print([p for p in range(2, range_to) if prime[p]])
+    # creating a boolean array first
+    prime = [True for i in range(range_to + 1)]
+    p = 2
+    while (p * p <= range_to):    
 
-def prime(range_from, range_to):
-  
-  allList = [x for x in range(2, range_to + 1)]
+        # If prime[p] is not changed, then it is a prime
+        if (prime[p] == True):
+
+            # Update all multiples of p
+            for i in range(p * 2, range_to + 1, p):
+                prime[i] = False
+
+        p += 1
 
-  ptr = 0
-  while True:
-    i = 2
-    while i * allList[ptr] <= range_to:
-      if i*allList[ptr] in allList:
-        allList.remove(i*allList[ptr])
-      i += 1
-    ptr += 1
-    if allList[ptr] ** 2 > range_to:
-      break
+    print([p for p in range(2, range_to) if prime[p]])
 
 
-  primeList = [x for x in allList if x > range_from]
-  print("Prime List Between ", range_from, " and ", range_to, " is")
-  print(primeList)
+def is_prime(num):
+        for i in range(2, int(num / 2) + 1):
+            if num % i == 0:
+                return False
+        return True
 
+
+def prime(range_from, range_to):
+    allList = [num for num in range(range_from, range_to + 1) if is_prime(num)]
+
+    print("Prime List Between", range_from, "and", range_to, "is")
+    print(allList)
 
 
 if __name__ == "__main__":
-  print("Enter the range of number")
-  range_from = int(input("From: "))
-  range_to = int(input("To: "))
-
-  prime(range_from, range_to)
-  SieveOfEratosthenes(range_to)
+    print("Enter the range of number")
+    range_from = int(input("From: "))
+    range_to = int(input("To: "))
 
+    prime(range_from, range_to)
+    SieveOfEratosthenes(range_to)