How to randomly segment lines from one text file into two different text files?

I have a text file with say, 100 lines, I want to randomly segment these lines into 80-20 lines into two separate text files, Using the code below but it's not doing proper partition. I am getting a different number of files. I should get 80 lines in file2 and 20 files in file1. can someone point out the error and plz suggest if there is a better way. please note in total.txt is the original file which needs to be segmented into file1 and file 2. '''

def partition(l, pred):
    fid_train=open('meta/file1.txt','w')
    fid_test = open('meta/file2.txt','w')
    for e in l:
        if pred(e):
            fid_test.write(e)
        else:
            #fid_train.write(e+'\n')
            fid_train.write(e)
    return fid_train,fid_test
lines = open("meta/total_list.txt").readlines()
lines1, lines2 = partition(lines, lambda x: random.random() < 0.2)    

'''