String comparison doesn’t seem to work for lines read from a file

I have a file named test.txt that contains the following:

Line 1
Line 2
Line 3
Line 4

I have simple Python program like this:

f = open("test.txt")

myline = "Line 3"
for line in f:
    print myline + " - " + line
    if myline == line:
        print "We have a match!"

if myline == "Line 3":
    print "This works."

I got this result:

Line 3 - Line 1

Line 3 - Line 2

Line 3 - Line 3

Line 3 - Line 4

This works.

Why doesn’t “We have a match!” get printed?

What did I miss?

Answers:

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Method 1

Why doesn’t “We have a match!” get printed? What did I miss?

If you will notice the output on console you are getting double n (newlines) one because of print second because in file every line has n at the end. Your file that looks like:

Line 1
Line 2
Line 3
Line 4

is basically: Line 1nLine 2nLine 3nLine 4 (assuming you don’t have any extra white spaces e.g. tabs, blank space).

In for loop: for line in f:, end char of line is n (and line that you think is 'Line 3' is actually 'Line 3n') Hence your if condition fails.

To remove that n just use str.strip([chars]); function. The method strip() returns a copy of the string in which all chars have been stripped from the beginning and the end of the string (default whitespace characters).

So, replace if myline == line: by if myline == line.strip() that is what @C.B.’s answer.

Method 2

Strip the newline character:

for line in f:
    print myline + " - " + line
    if myline == line.strip():
        print "We have a match!"

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0