Added comments

02a.py

@@ -11,31 +11,35 @@ def main(lines):
 		Ignore any doubles or triples past the first set.
 		At the end, multiply x2 by x3 to get the checksum.
 	"""
-	x2, x3 = 0, 0
-	for line in lines:
-		chars = {}
-		gota2, gota3 = False, False
-		for char in line:
-			if char in chars.keys():
-				chars[char] += 1
-			else:
-				chars[char] = 1
-		for k,v in chars.items():
-			if v == 2 and not gota2:
-				x2 += 1
-				gota2 = True
-			if v == 3 and not gota3:
-				x3 += 1
-				gota3 = True
-			if gota2 and gota3:
-				break
-	print("Totals: x2 {}, x3 {}".format(x2, x3))
-	print("Checksum: {}".format(x2 * x3))
+	x2, x3 = 0, 0 # independent counters. Count how many lines had at least one pair/triplet
+	for line in lines: # iterate over each line in the input file
+		chars = {} # dictionary to hold character: count values (e.g. a:1, b:2) for the current line
+
+		for char in line: # iterate over characters in each line
+			if char in chars.keys(): # if we've seen the character before in this line
+				chars[char] += 1 	 # increment its count in the dictionary by 1
+			else:					 # but if we haven't
+				chars[char] = 1		 # then add it to the dictionary
+
+		gota2, gota3 = False, False  # Do we have at least one pair/triplet in the line?
+		for k,v in chars.items():    # iterate over the dictionary
+			if v == 2 and not gota2: # if the count is 2, we have a pair; if we didn't already have one, then
+				x2 += 1				 # increment the "pair" counter by 1, and
+				gota2 = True		 # track that we've seen one so we don't accidentally add any more
+			if v == 3 and not gota3: # if the count is 3, we have a triplet; if we didn't already have one, then
+				x3 += 1				 # increment the triplet counter by 1, and
+				gota3 = True		 # track that we've seen one so we don't accidentally add any more
+
+			if gota2 and gota3:		 # if at this point we've seen both a pair and a triplet,
+				break				 # we don't need to check any more characters, so break the loop
+
+	print("Totals: x2 {}, x3 {}".format(x2, x3)) # print our totals
+	print("Checksum: {}".format(x2 * x3)) # print the totals multiplied, which is our checksum
 
 
 if __name__ == "__main__":
-	lines = []
-	with open("02in.txt","r") as f:
-		for line in f:
-			lines.append(line.strip())
-	main(lines)
+	lines = [] # an empty list for the lines in the input file
+	with open("02in.txt","r") as f: # open the file. "with" means we don't have to close it
+		for line in f: # iterate over the lines in the input file
+			lines.append(line.strip()) # strip the newline character, then add it to the list
+	main(lines) # and pass the list to our main function.