python不通过readlines（）进行迭代

Question

I have a text file with just strings on each row. I want to get python to look at a row and then check if that string is in a list and if it is not add it, else skip to next line. Later I will use collections to count total occurrences of each list item.

testset = ['2']
# '2' is just a "sanity check" value that lets me know I am extending list

file = open('icecream.txt')

filelines = file.readlines()

for i in filelines:
    if i not in testset:
    testset.extend(i)
else:
    print(i, "is already in set")

print(testset)

I was expecting to get:

testset = ['2', 'chocolate', 'vanilla', 'AmericaConeDream', 'cherrygarcia', ...]

instead I got:

testset = ['2', 'c', 'h', 'o', 'c', 'o' ....]        

Not sure what is happening here. I have tried to run this using: for i in file:

As I believe I read on another post that the open() was a iterator in and of itself. Can someone enlighten me as to how I get this iteration to work?

Answer 1

extend() iterates over the elements (in this case, the characters) of its argument, and adds each of the them individually to the list. Use append() instead:

    testset.append(i)

If you don't care about the order in which the lines appear in testset , you could use a set instead of a list. The following one-liner will create a set containing every unique line in the file:

testset = set(open('icecream.txt'))

Answer 2

You can think of extend as append for an an iterable of values rather than just one. Because you plan to use a counter to counter the files anyway, I would do the following to key the unique values:

with open('text.txt') as text:
    data = Counter(i for i in text) # try data.keys()

Answer 3

EDIT: look at NPE's answer : it's basically the same, but more elegant and pythonic.

Try reading and splitting and reducing in one go:

textset = set(file.read().split('\n'))