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Remove current line from file [duplicate]

This question already has answers here:
Is it possible to modify lines in a file in-place?
(5 answers)
Closed 2 years ago.
Consider a file with the following lines:
remove
keep
remove
Is it possible to remove the current line while iterating the file lines?
for word in file:
if word != "keep":
remove_line_from_file
In the end the file should just the line with word keep.
I know I could create a file with the remaining words but I was hoping to keep the same file.

Python has a nice library named fileinput which allows you to modify files inplace. You can print what you want to keep back into the file:
with fileinput.input(filename, inplace=True) as lines:
for line in lines:
if line == 'keep':
print(line,)

No, but you can extract all the contents of the file beforehand, modify the text, and then rewrite them back into the file:
with open('file.txt','r') as f:
lines = f.readlines()
with open('file.txt','w') as f:
f.write(''.join([ln for ln in lines if 'keep' in ln])) # Writes all the lines back to file.txt that has the word `keep` in them

python append a new line to end of huge file after the last non-whitepsace lines [duplicate]

This question already has answers here:
Most efficient way to modify the last line of a large text file in Python
(2 answers)
Get last n lines of a file, similar to tail
(35 answers)
Closed 3 years ago.
I am currently appending like this:
with open(filename, "a") as fh:
fh.write("some line")
This assumes that the last line of the file is a new line and that it is empty
in the case where the file doesn't end with a new line, my code appends to the last line
i.e.
last line of textsome line
and not:
last line of text
some line
in the case where the file ends with many "empty" new lines, the line is added after them , which isn't good either.
i.e.
...
...
last line
\n
\n
\n
...
some line
I want my line to be added on a new line after the last meaningful existing line (line with text that is non-empty)
The text files are quite large, 10-20 gigs each , so I can't easily "read" and then "chomp".
I know that the files won't have more then 1-10 empty lines at the end (usually only a single empty line at the end hence the code usually works and rarely fails)
is there a variation on open (file, 'a') to seek to end of content of file on a new line?

How to read each line in a file backwards using Python [duplicate]

This question already has answers here:
How do I reverse a string in Python?
(19 answers)
Closed 3 years ago.
I'm trying to read a file (example below), line by line, backwards using Python.
abcd 23ad gh1 n d
gjds 23iu bsddfs ND31 NG
Note: I'm not trying to read the file from the end to the beginning, but I want to read each line starting from the end, i.e d for line 1, and NG for line 2.
I know that
with open (fileName) as f:
for line in f:
reads each line from left to right, I want to read it from right to left.

Try this:
with open(fileName, 'r') as f:
for line in f:
for item in line.split()[::-1]:
print(item)

If your file is not too big, you can read lines in reverse easily
with open(fileName) as f:
for line in reversed(f.readlines()):
# do something
Otherwise, I believe you'd have to use seed.

How to save line by line a file.txt in array or table? [duplicate]

This question already has answers here:
How to read the entire file into a list in python?
(6 answers)
Closed 5 years ago.
I would like to save a file.txt line by line in variable (array or list)
.So if the file.txt is:
hi there
what's up
I want my code to save it line by line in the same variable making a table so I can access easily each line when I want using that variable. And what can I do if I wanna access only line 2? It is supposed I don't know how many lines the file.txt has.
Thank you very much!

Well it is super easy in Python:
text_file = open("filename.txt", "r")
# Splits the element by "\n"
lines = text_file.readlines()
text_file.close()
#Print List of Lines in your File
print(lines)
#Print Number of Lines in your File
print(len(lines))
#Access Second Line in your file
print(lines[1])# Since python is zero indexed

How to read text file line by line and do something for a particular line? [duplicate]

This question already has answers here:
How to jump to a particular line in a huge text file?
(17 answers)
Closed 8 years ago.
I want to read a text file line by line. I found how to read line by line by searching but not how to call a specific line in a text file. Basically, i want to do something with particular lines( like the first line, the second line, the third line, etc):
if particular_line is something:
....
Also, how can i do something like this:
if return_from_another_function in file:
....
Basically, i want an example of how i could do that if it's possible.

f = open('filename', 'r')
lines = f.readlines()
now you get a list type object lines which you can use to access particular line or iterate and search for particular line.

Probably this will help:
myfile = open(filename, "rb", 0)
for line in myfile
if(line is "your string to be compared")
print "do something here"

The standard linecache module makes this a snap:
import linecache
theline = linecache.getline(thefilepath, desired_line_number)
For your second que (from Ans):
If your file is not too large, you can read it into a string, and just use that (easier and often faster than reading and checking line per line):
if 'blabla' in open('example.txt').read():
print "true"