Converting a string into a float that includes the negative

[phamtony33 at gmail.com]

I am having issue with converting the string into a float because there is a negative, so only end up with "ValueError: invalid literal for float(): 81.4]"

def contains_words(word,msg):
	if word in msg:
		return true
	else:
		return false
		
def get_tweet(tweet_line):
	part_list = tweet_line.split('\t')
	tweet = part_list[3]
	return tweet

def get_longitude(tweet_line):
	part_list = tweet_line.split('\t')
	gps = part_list[0]
	gps_list = gps.split(', ')
	long = gps_list[1]
	long1 = long[1:]
	longitude = float(long1)
	return longitude

a = get_longitude("[41.3, -81.4]\t6\t2011-08-28 19:02:28\tyay. little league world series!")
print a

the answer should be 
get_longitude("[41.3, -81.4]\t6\t2011-08-28 19:02:28\tyay. little league world series!") → -81.4