CODEWITHSUNDEEP
python
Fang
Fang

Reputation: 844

how to skip certain line in text file and keep reading the next line in python?

I have been searching for this answer but did not quite get it.

I have a text file that looks like this

who are you????
who are you man?
who are you!!!!
who are you? man or woman?

I want to skip the line with man in it and print

who are you????
who are you!!!!

My code so far

f = open("test.txt", "r")
word = "man"
for line in f:
    if word in line:
        f.next()
    else:
        print line

This prints the first line only

who are you????

How should I troubleshoot this problem?

Thank you for your help.

Upvotes: 3

Views: 17813

Answers (3)

Eric Duminil
Eric Duminil

Reputation: 54223

Problem

With your current code, when the current line contains "man" :

  • you don't print anything. That's correct.
  • you also skip the next line. That's your problem!
  • f.next() is already called implicitely by for line in f: at each iteration. So you actually call f.next() twice when "man" is found.
  • If the last line of your file contains a "man", Python will throw an exception because there's no next line.

You might have been looking for continue, which would also achieve the desired result but would be complex and unneeded. Note that it's called next in Perl and Ruby, which might be confusing.

Example

who are you????            # <- This line gets printed, because there's no "man" in it
who are you man?           # word in line is True. Don't print anything. And skip next line
who are you!!!!            # Line is skipped because of f.next()
who are you? man or woman? # word in line is True. Don't print anything. 
                           #   Try to skip next line, but there's no next line anymore.
                           #   The script raises an exception : StopIteration

Correct code

Don't forget to close the file. You can do this automatically with with :

word = "man"
with open("test.txt") as f:
    for line in f:
        if not word in line:
            print line, # <- Note the comma to avoid double newlines

Upvotes: 5

Giordano
Giordano

Reputation: 5570

It's not necessary to add an if else statement in for loop, so you can modify your code in this way:

f = open("test.txt", "r")
word = "man"
for line in f:
    if not word in line:
        print line

Furthermore, the issue in your code is that you are using f.next() directly in a for loop used to scan the file. This is the reason because when the line contains "man" word, your code skips two lines.

If you want preserve if else statement because this is only an example of a more complex problem, you can use the following code:

f = open("test.txt", "r")
word = "man"
for line in f:
    if word in line:
        continue
    else:
        print line

Using continue, you skip one loop's iteration, and so you can reach your goal.

As Alex Fung suggests, would be better use with, so your code would become like this:

with open("test.txt", "r") as test_file:
    for line in test_file:
        if "man" not in line:
            print line

Upvotes: 5

Tore
Tore

Reputation: 51

How about

f = open("test.txt", "r")
word = "man"
for line in f:
    if not word in line:
        print line

Upvotes: 1

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