if (suffval != '') and (suffval not in allowed):
if (suffval is not None)
if (not len(suffval))
if (suffval not in allowed) & (suffval is not None) & (len(suffval) != 0):
By "records without values" do you mean records with NULL or records with just an empty string? If a string is empty it will have length zero.
if (suffval not in allowed) & (suffval is not None) & (len(suffval) != 0): # flag record
if (suffval != ' ') and (suffval not in allowed)
if (not suffval.isspace()) and (suffval not in allowed):