Update Lesson 2 Task %*f#ncA0#>? to work without libraries

Lesson_2/We know/dumb_decryptor.py

@@ -5,7 +5,35 @@
 # Return codes:
 # 0 - OK
 
-rot13 = str.maketrans('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz', 
-   'NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm')
+def isUppercase(chr):
+	if chr >= "A" and chr <= "Z":
+		return True
+	else:
+		return False
 
-print(input("Enter message: ").translate(rot13))
+def isLowercase(chr):
+	if chr >= "a" and chr <= "z":
+		return True
+	else:
+		return False
+
+def isLetter(chr):
+	if isUppercase(chr) or isLowercase(chr):
+		return True
+	else:
+		return False
+
+string = input("Enter message: ")
+newstring = ''
+
+for i in range(len(string)):
+	if not isLetter(string[i]):
+		continue
+	uppercase = isUppercase(string[i])
+	newOrd = ord(string[i]) + 13
+	if isLetter(chr(newOrd)) and uppercase == isUppercase(chr(newOrd)):
+		newstring += chr(newOrd)
+	else:
+		newstring += chr(newOrd - 26)
+
+print(newstring)