def read_topic(self, input_file="topic_list/topic_0.txt", split_sign=":"):
"""
Read in a specific topic from a file named <input_file>
:param input_file: the name of the file that stores the topic
:return: a topic containing a list of word distribution tuples
"""
# read in all ines of input except the last line which is an empty new line
input_file = open(input_file, 'r')
word_dist = input_file.readlines()
# Create the topic object
# The topic object contains a list of word distribution tuples
topic = Topic()
for dist in word_dist:
dict = dist.strip().split(split_sign)
topic.add((dict[0], float(dict[1])))
return topic
