Python: How to loop using a for loop more times than there are items in the file

Question

theFile   = open('theFile', 'r+')
fileCheck = open('fileCheck', 'r+')

numOfFiles = 3
currentNum = 0

def check():
    for i in theFile:
        for lines in fileCheck:
            if i == lines:
                print("We already have " + i)
                break 
            else:
                print("We don't have " + i)
                break

check()

fileCheck.close()
theFile.close()

---

fileCheck contents are:

line 1
line 2
line 4
line 5

theFile contents are:

line 1
line 2
line 3
line 4
line 5
line 6
line 7
line 8
line 9
line 10

I am trying to loop through both files to check if the contents from theFile are in fileCheck . For example, if "line 1" is already in fileCheck , I want it to ignore that and keep moving. When it gets to "line 3" which is not in fileCheck , I want it to do a series of code, then when it gets to "line 4" it should skip it and "line 5" , too. From line 6-10 it performs the code I tell it to do. I know this is not working because there are only 4 lines in fileCheck so it only performs that loop 4 times, and doesn't get all 10 lines. I want it to loop through all 10 lines but I can't figure out how.

Answer 1

Here

for i in theFile:
    for lines in fileCheck:
        ...

it looks like you're trying to iterate over fileCheck more than once. In that case, you will have to reset it somehow (for example, repeat the

fileCheck = open('fileCheck', 'r+')

but you could start by reading the whole file at once:

fileCheck = list(open('fileCheck', 'r+')

Have you considered doing

theFile = set(open('theFile, 'r+'))
fileCheck = set(open('fileCheck', 'r+'))

and then using set differences: theFile - fileCheck are the lines that are in the first but not the second set; line in theFile is True or False, and so on.