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Slice a given txtfile and write only part of it in a newfile in python

This is my original .txt data:
HKEY_CURRENT_USER\SOFTWARE\7-Zip
HKEY_CURRENT_USER\SOFTWARE\AppDataLow
HKEY_CURRENT_USER\SOFTWARE\Chromium
HKEY_CURRENT_USER\SOFTWARE\Clients
HKEY_CURRENT_USER\SOFTWARE\CodeBlocks
HKEY_CURRENT_USER\SOFTWARE\Discord
HKEY_CURRENT_USER\SOFTWARE\Dropbox
HKEY_CURRENT_USER\SOFTWARE\DropboxUpdate
HKEY_CURRENT_USER\SOFTWARE\ej-technologies
HKEY_CURRENT_USER\SOFTWARE\Evernote
HKEY_CURRENT_USER\SOFTWARE\GNU
And I need to have a new file where the new lines contain only part of those strings, like:
7-Zip
AppDataLow
Chromium
Clients
...
how to do it in python?

Try this:
## read file content as string
with open("file.txt", "r") as file:
string = file.read()
## convert each line to list
lines = string.split("\n")
## write only last part after "\" in each line
with open("new.txt", "w") as file:
for line in lines:
file.write(line.split("\\")[-1] + "\n")

One approach would be to read the entire text file into a Python string. Then use split on each line to find the final path component.
with open('file.txt', 'r') as file:
data = file.read()
lines = re.split(r'\r?\n', data)
output = [x.split("\\")[-1] for x in lines]
# write to file if desired
text = '\n'.join(output)
f_out = open('output.txt', 'w')
f_out.write(text)
f_out.close()

Overwriting lines in text file [duplicate]

How can I insert a string at the beginning of each line in a text file, I have the following code:
f = open('./ampo.txt', 'r+')
with open('./ampo.txt') as infile:
for line in infile:
f.insert(0, 'EDF ')
f.close
I get the following error:
'file' object has no attribute 'insert'

Python comes with batteries included:
import fileinput
import sys
for line in fileinput.input(['./ampo.txt'], inplace=True):
sys.stdout.write('EDF {l}'.format(l=line))
Unlike the solutions already posted, this also preserves file permissions.

You can't modify a file inplace like that. Files do not support insertion. You have to read it all in and then write it all out again.
You can do this line by line if you wish. But in that case you need to write to a temporary file and then replace the original. So, for small enough files, it is just simpler to do it in one go like this:
with open('./ampo.txt', 'r') as f:
lines = f.readlines()
lines = ['EDF '+line for line in lines]
with open('./ampo.txt', 'w') as f:
f.writelines(lines)

Here's a solution where you write to a temporary file and move it into place. You might prefer this version if the file you are rewriting is very large, since it avoids keeping the contents of the file in memory, as versions that involve .read() or .readlines() will. In addition, if there is any error in reading or writing, your original file will be safe:
from shutil import move
from tempfile import NamedTemporaryFile
filename = './ampo.txt'
tmp = NamedTemporaryFile(delete=False)
with open(filename) as finput:
with open(tmp.name, 'w') as ftmp:
for line in finput:
ftmp.write('EDF '+line)
move(tmp.name, filename)

For a file not too big:
with open('./ampo.txt', 'rb+') as f:
x = f.read()
f.seek(0,0)
f.writelines(('EDF ', x.replace('\n','\nEDF ')))
f.truncate()
Note that , IN THEORY, in THIS case (the content is augmented), the f.truncate() may be not really necessary. Because the with statement is supposed to close the file correctly, that is to say, writing an EOF (end of file ) at the end before closing.
That's what I observed on examples.
But I am prudent: I think it's better to put this instruction anyway. For when the content diminishes, the with statement doesn't write an EOF to close correctly the file less far than the preceding initial EOF, hence trailing initial characters remains in the file.
So if the with statement doens't write EOF when the content diminishes, why would it write it when the content augments ?
For a big file, to avoid to put all the content of the file in RAM at once:
import os
def addsomething(filepath, ss):
if filepath.rfind('.') > filepath.rfind(os.sep):
a,_,c = filepath.rpartition('.')
tempi = a + 'temp.' + c
else:
tempi = filepath + 'temp'
with open(filepath, 'rb') as f, open(tempi,'wb') as g:
g.writelines(ss + line for line in f)
os.remove(filepath)
os.rename(tempi,filepath)
addsomething('./ampo.txt','WZE')

f = open('./ampo.txt', 'r')
lines = map(lambda l : 'EDF ' + l, f.readlines())
f.close()
f = open('./ampo.txt', 'w')
map(lambda l : f.write(l), lines)
f.close()

Can you write to the middle of a file in python?

I would like to write to the middle of a line in a file.
for exemple i have a file:
Text.txt:
"i would like to insert information over here >>>>>>>[]<<<<<<<<"
Is is it possible to precise an index where: file.write() has to start writing?
I have started with this:
file = open(file_path, 'w')
file.write()

I think what you can do is to substitute already existing characters with the same amount of other characters you want. You can open a file, locate the starting point, and start writing. But you will overwrite all the following bytes if you use f.write(). If you want to "insert" something inbetween, you have to read and rewrite all the following content of the file.
Overwrite:
with open('text.txt', 'w') as f:
f.write("0123456789")
# now the file 'text.txt' has "0123456789"
with open('text.txt', 'r+b') as f:
f.seek(-4, 2)
f.write(b'a')
# now the file 'text.txt' has "012345a789"
Insert:
with open('text.txt', 'w') as f:
f.write("0123456789")
# now the file 'text.txt' has "0123456789"
with open('text.txt', 'r+b') as f:
f.seek(-4, 2)
the_rest = f.read()
f.seek(-4, 2)
f.write(b'a')
f.write(the_rest)
# now the file 'text.txt' has "012345a6789"

import fileinput
file = [The file where the code is]
for line in fileinput.FileInput(file, inplace=1):
if [The text that should be in that line] in line:
line = line.rstrip()
line = line.replace(line, [The text that should be there after this file was run])
print (line,end="")
As text in that line you should enter the whole line, else it could not work (I didn't test it out though)

Python read .txt and split words after symbol #

I have a large 11 GB .txt file with email addresses. I would like to save only the strings till the # symbol among each other. My output only generate the first line.I have used this code of a earlier project. I would like to save the output in a different .txt file. I hope someone could help me out.
my code:
import re
def get_html_string(file,start_string,end_string):
answer="nothing"
with open(file, 'rb') as open_file:
for line in open_file:
line = line.rstrip()
if re.search(start_string, line) :
answer=line
break
start=answer.find(start_string)+len(start_string)
end=answer.find(end_string)
#print(start,end,answer)
return answer[start:end]
beginstr=''
end='#'
file='test.txt'
readstring=str(get_html_string(file,beginstr,end))
print readstring

Your file is quite big (11G) so you shouldn't keep all those strings in memory. Instead, process the file line by line and write the result before reading next line.
This should be efficient :
with open('test.txt', 'r') as input_file:
with open('result.txt', 'w') as output_file:
for line in input_file:
prefix = line.split('#')[0]
output_file.write(prefix + '\n')

If your file looks like this example:
user#google.com
user2#jshds.com
Useruser#jsnl.com
You can use this:
def get_email_name(file_name):
with open(file_name) as file:
lines = file.readlines()
result = list()
for line in lines:
result.append(line.split('#')[0])
return result
get_email_name('emails.txt')
Out:
['user', 'user2', 'Useruser']

How to remove line that contain a certain string in python

I have a text file that looks like this
Big:house
small:door
Big:car
Small:chair
Big:plane
How to I remove the lines that contain the word "big" so it may look like this, I dont want to create a new file all together though
small:door
small:chair
Here was my attempt
with open('QWAS.txt','r') as oldfile:
for line in oldfile:
if bad_words in line:
newfile.write(line)

This is what we can do:
Read data to string (remove rows that start with 'big')
Go to the start of file (seek)
Write the string
Truncate (remove overflow)
And now to the code, open it in read and write mode:
with open('QWAS.txt','r+') as f:
data = ''.join([i for i in f if not i.lower().startswith('big')]) #1
f.seek(0) #2
f.write(data) #3
f.truncate() #4

Try this:
newfile = r'output.txt'
oldfile = r'input.txt'
with open(newfile, 'w') as outfile, open(oldfile, 'r') as infile:
for line in infile:
if if line[:5].lower() == 'small':
outfile.write(line)
#output
small:door
Small:chair
Of course, this assumes you want to eliminate rows where small or Small is to the left of the colon. Additionally, you will have a new file output, as I don't think you really want to update your input file.

You can try using regular expressions
import re
oldfile = open('QWAS.txt','r')
newfile = open('newfile.txt','w')
for line in oldfile:
if re.search('[Ss]mall',line):
newfile.write(line)
oldfile.close()
newfile.close()
Which gives the output file "newfile.txt"
small:door
Small:chair
If you just take every line that doesn't have small and write it to a new file "newfile2.txt"
import re
oldfile = open('QWAS.txt','r')
newfile = open('newfile.txt','w')
newfile2 = open('newfile2.txt','w')
for line in oldfile:
if re.search('[Ss]mall',line):
newfile.write(line)
else:
newfile2.write(line)
oldfile.close()
newfile.close()
newfile2.close()