比较字符串Python的最快方法

Question

Situation: Comparing strings in fileA with pre-defined strings in fileB. Example of said function in my code:

string = open('fileA', 'r')
stringlist = open('fileB', 'r')

//compare the strings
for i in string:
    for j in stringlist:
        if i == j:
            print("Same String found!" + i + " " + j)

Problem: In my actual program, string contains more than 200 strings, while stringlist is a file with more than 50,000 strings. The nested for loop, as I have read, is slow as a comparison function.

Question: What is the fastest way to compare the two files' content?

Additional information 1: Both files are CSV files, and are opened in my program as CSV-delimited.

Additional information 2: Strings are md5 hashes (32 characters).

Additional information 3: I am open to other ways to store the strings, ie Compare the strings on-the-fly instead of saving it to fileA.

Additional information 4: I am also open to other methods or modules that I can use (ie: Threading/parallel processing) -- speed is the key here.

Answer 1

If you are okay with not printing duplicates, using set.intersection should be really fast:

list1 = ["hello", "world", "foo"]
list2 = ["foo", "bar", "baz"]

set(list1).intersection(list2)
# {'foo'}

Answer 2

You should use sets :

setA = set(listA)
setB = set(listB)
common = setA.intersection(setB)

common now holds all the strings that are present in both lists

You can also do this with a one-liner:

common = set(listA).intersection(set(listB))

If you can do this comparison "on the fly" it is of course better and faster than saving the lists to a file and then reading again from that file, you gain nothing by doing that.

And of course, to print duplicates:

for x in common:
    print(x)