g = 0
c = 0
a = 0
t = 0

class ProcessData(threading.Thread):
    def __init__(self, batch):
            threading.Thread.__init__(self)
            self.batch = batch
            self.g = 0
            self.c = 0
            self.a = 0
            self.t = 0
    def run(self):
            global g, c, a, t
            threadLock.acquire()
            for line in self.batch:
                    line = line.lower()
                    for nucleotide in line:
                            if nucleotide == "g":
                                    self.g += 1
                            if nucleotide == "c":
                                    self.c += 1
                            if nucleotide == "a":
                                    self.a += 1
                            if nucleotide == "t":
                                    self.t += 1
            g += self.g
            c += self.c
            a += self.a
            t += self.t
            print(g+c+a+t)
            threadLock.release()

File "gc_threaded.py", line 49, in run t += self.t
TypeError: unsupported operand type(s) for +=: 'ProcessData' and 'int'