Comparing lines of two text files in python [duplicate]

Answer 1

Don't just read the files line by line but filter each line: extract the stuff within ( ) and remove BlockNum: if it exists. Something like this:

def getRecords(fn):
    for line in open(fn, 'r'):
        entry = line.rstrip()[line.find('(')+1:-1]
        if entry.startswith('BlockNum:'):
            yield entry[10:]
        else:
            yield entry

import itertools
filesAreEqual = all(a == b for a, b in itertools.izip(getRecords("file1.txt"),
                                                      getRecords("file2.txt")))

Answer 2

What I understand from your code is that compare the first line of file1 to all the lines in file2.

What you actually want to do is to read a line in file1, compare it to file2 if it is different reutun "different" and finish. Otherwise, finish comparing all the lines and return equal.

I don't like the answers in how to compare lines in two files are same or different in python since they load all the files in the memory.

What I would do is something like

f1 = open("file1")
f2 = open("file2")
line1 = next(f1)
line2 = next(f2)
found_different = False
while line1 and line2:
   if line1 != line2:
      found_different = True
      break
   line1 = next(f1)
   line2 = next(f2)

if not line1 and not line2 and not found_different:
   print "equal"
else:
   print "different"

Answer 3

Your problem is that in your second for loop, you say:

if line==line2:

When it needs to be:

if line1==line2:

Since it has no idea what line is, you get errors. Here is the corrected code, after testing.

fin1=open("file1.txt","r")
fin2=open("file2.txt","r")
for line1 in fin1:
    for line2 in fin2:
        if line1==line2:
            print "same data"
        else:
            print "data are different"
fin1.close()
fin2.close()

Happy coding!