Added comments in the code to provide a little bit more insight into what's happening.

tokenizer.py

@@ -1,11 +1,10 @@
 import ptoken as token
 
 def get_tokens_from_expression_string(expression_string):
-
-	#Takes user input of an actuarial formula and parses the formula to id its components.
-	#:return: tokens (List of objects of CToken class).
+	# Takes user input (in the format of a string) of an actuarial formula and parses the formula to its components.
+	# Returns the list of Token objects that represent the string expression.
 	
-	tokens = []  # List of objects of CToken class
+	tokens = []  # List of objects of Token class
 	tmp = ""
 	parsing_number = False
 	symbols_dic = {}  # Dictionary to keep track of the no. of times each variable appears.
@@ -41,7 +40,7 @@ def get_tokens_from_expression_string(expression_string):
 					parsing_number = False
 					tmp = ""
 			elif expression_string[i + 1].isalpha():
-				#Must be a variable.
+				# Must be a variable.
 				if tokens[-1].type == token.TokenType.exp_start:
 					variable_is_negative = True
 				elif token.TokenType.get_operator(tokens[-1].value) != token.TokenType.unknown:
@@ -94,10 +93,14 @@ def get_tokens_from_expression_string(expression_string):
 			if parsing_number:
 				tokens.append(token.Token(tmp, token.TokenType.constant))
 				tokens.append(token.Token("*", token.TokenType.multiply))
+			# Check to see if the encountered variable, which is effectively a single character,
+			# has been seen before. If it has been then simply increment the number that represents how many times it's been seen
+			# else, add a new entry for it in the dictonary 'symbols_dic'.
 			if c in symbols_dic.keys():
 				symbols_dic[c] += 1
 			else:
 				symbols_dic[c] = 1
+			# Afterwards, add the variable with the count of the times it's been seen as a token object to the list of tokens.
 			tokens.append(token.Token(c + str(symbols_dic[c]), token.TokenType.variable, variable_is_negative))
 			variable_is_negative = False
 			parsing_number = False
@@ -106,12 +109,16 @@ def get_tokens_from_expression_string(expression_string):
 	return tokens
 
 def peek_list(tokens):
+	# Returns the last Token object in the list, else throws an error.
     if tokens:
         return tokens[-1]
     else:
         raise IndexError("The token list is empty.", tokens)
 
 def replace_variables(tokens, new_constants):
+	# Searches and replaces variable Tokens with Constant TokenType Token objects. Doing so enables the calc_engine to never have
+	# to even know variable token types exist.
+	# Returns a list of Token objects with the variables replaced by the supplied list of new constants.
 	newTokenList = []
 	for t in tokens:
 		if t.type == token.TokenType.variable:
@@ -125,6 +132,7 @@ def replace_variables(tokens, new_constants):
 	return newTokenList
 	
 def print_token_list(tokens):
+	# Prints the list of Tokens to standard out.
 	for tk in tokens:
 		if tk.type == token.TokenType.variable:
 			if tk.is_negative_variable:
@@ -136,6 +144,7 @@ def print_token_list(tokens):
 	print()
 	
 def stringify_token_list(tokens):
+	# Returns a string that represents the list of Tokens.
 	text = ''
 	for tk in tokens:
 		text += str(tk.value)