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i write on a file and read it but it seems when i run again

I want to write a file that says hello guys how are you but each word must be an item of list. Here is my code. It shows nothing when I run it, when I run second time it shows item by item as I want. But when I click text file, it is written two times.
with open('stavanger.txt','r+') as f: # file closes itself with with open as filename command
words = ['hello\n','guys\n','how\n', 'are\n','you\n']
f.writelines(words)
for i in f:
x=i.rstrip().split(',')#turn text file into list and we seperate list items by comma .
print(x)

The problem is that writing to a file uses a buffer. So after the line f.writelines(words) nothing really happened. Only the buffer changed.
In effect, the file still haven't changed and the file pointer is still at the beginning of the file. So the second time you run your code you see the content printed, which leaves the file pointer at the end of the file and only then the buffer is passed to the file and you have the duplicated content.
Simply use mode='w' if you just want to write to a file...

You start reading the file from where the writing stopped. It is better to open the file first for writing, then for reading
Something like this
with open('stavanger.txt', 'w') as f: # file closes itself with with open as filename command
words = ['hello\n', 'guys\n', 'how\n', 'are\n', 'you\n']
f.writelines(words)
with open('stavanger.txt', 'r') as f:
for i in f:
x = i.rstrip().split(',') # turn text file into list and we seperate list items by comma .
print(x)

How do I copy specific strings from a text file with python?

I am working in the field of astronomy, and the process that I use to unzip the images that I get from the telescopes can be very tedious. The format that the images come in is 'fits.fz' which stands for fits.fits-zipped. I want to decompress these into just '.fits'. I have already I'm working on a program that simplifies this process of decompressing. I have created a graphical interface with two buttons through Python and Tkinter. The first button creates a text file named 'list.txt' and then executes a pre-existing .bat file which dumps the names of every file in a specific directory that ends with 'fits.fz' into 'list.txt'. The first button is also supposed to copy the specific names of the files into a very specific place in another bat file. The other .bat file is called 'Decompress.bat' and is supposed to use the following command for each file in 'list.txt':
C:\ds9\ds9.exe
C:\directory\FITS FILE HERE
-savefits
I would like for the python program to be able to copy specific sections from a line of code and paste them where 'FITS FILE HERE' is.
The following is the function that is executed when the first button is pressed.
f = open('C:/jah/list.txt')
f1 = open('C:/jah/decompress.bat', 'a')
def begin_wombocombo(): #Is function for first button
open('C:/jah/list.txt', 'w').close() #Clears 'list.txt'
open('C:/jah/decompress.bat', 'w').close() #Clears 'decompress.bat'
subprocess.call([r'C:/jah/newbat.bat']) #Dumps directory into 'list.txt'
doIHaveToCopyTheLine=False #Bool for whether or not the program has to copy line
for line in f.readlines(): #loops through all instances to find fz files and then pastes them into decompress.bat
if 'fits.fz' in line:
doIHaveToCopyTheLine=True
if doIHaveToCopyTheLine:
f1.write(line)
f1.close()
f.close()
The issue with this is that it only copies the lines of text that has the fits.fz files. This means that it copies everything else on the line such as when the file was created. Is there any way to simply copy and paste the fits.fz file alone? How would I go about working these strings into the .bat file?
Thank you for your time, and btw the second button just executes 'decompress.bat' which is the file with the commands to unzip the images.

I think in Python, something like this would do the trick, without writing out batch files etc.
import os
import subprocess
target_directory = 'C:\\directory\\' # change this as required
zipped_files = [x for x in os.listdir(target_directory)
if x.lower().endswith('.fits.fz')]
for filename in zipped_files:
subprocess.call([r'C:\ds9\ds9.exe', os.path.abspath(filename), '-savefits'])

python write method append

I'm stuck in a very basic problem of I/O in python. I'd like to insert some line in existing file (called ofe, output file), extracted from an source file (called ife, input file) according to arguments passed by user as stored in an list called lineRange (which has an index idx and values lineNumber).
This is the result:
for ifeidx,ifeline in enumerate(ife,1): #for each line of the input file...
with open(outFile,'r+') as ofe:
for idx,lineNumber in enumerate(lineRange,1): #... check if it's present in desired list of lines...
if (ifeidx == lineNumber): #...if found...
ofeidx = 0
for ofeidx, ofeline in enumerate(ofe,1):
if (ofeidx == idx): #...just scroll the the output file and find which is the exact position in desired list...
ofe.write(ifeline) #...put the desired line in correct order. !!! This is always appending at the end of out file!!!!
break
Problem is, the write() method is always pointing to the end of file, appending the lines instead of inserting them when scrolling the output file.
I really don't understand what's happening since the file is open in read+write (r+) mode, neither append (a) nor read+append (r+a) mode, .
I'm also aware that code will (should) overwrite the output file lines. Additional information are the OS WIndow7, Python version 2.7 and development tool is Eclipse with PyDev 3.7.1.xx
Any suggestion on what I'm doing wrong?

You can start by reading the whole file with readlines(), which will return a list. After that you just need to do list.insert(index, value) and write it again back to the file.
with open(outFile, "r") as f:
data = f.readlines()
data.insert(index, value)
with open(outFile, "w+") as f:
f.write(data)
Of course you should change this approach if you are dealing with a huge file.
By the way, if you are not using the with statement you should close the file in the end.

Python won't write each time new lines into text file

I have two python files, both of them in the same folder. The main file executes the whole function, making my program what I want it to do. The other file writes data to a text file.
However, there's one issue with writing data to the text file: instead of writing each time new lines to the existing text, it completely overwrites the whole file.
File responsible for writing data(writefile.py)
import codecs
def start(text):
codecs.open('D:\\Program Files (x86)\\Python342\\passguess.txt', 'a', 'utf-8')
with open('D:\\Program Files (x86)\\Python342\\passguess.txt', 'w') as file:
file.write(text + '\n')
I've tried out couple of things such as .join(text) or running the code from writefile.py in the main file. Nothing seems to work..

The problem lies with the line
with open('D:\\Program Files (x86)\\Python342\\passguess.txt', 'w') as file:
this one opens the file in write mode, to append you want 'a' option so just change to
with open('D:\\Program Files (x86)\\Python342\\passguess.txt', 'a') as file:
and you should be fine

How to erase the file contents of text file in Python?

I have text file which I want to erase in Python. How do I do that?

In python:
open('file.txt', 'w').close()
Or alternatively, if you have already an opened file:
f = open('file.txt', 'r+')
f.truncate(0) # need '0' when using r+

Opening a file in "write" mode clears it, you don't specifically have to write to it:
open("filename", "w").close()
(you should close it as the timing of when the file gets closed automatically may be implementation specific)

Not a complete answer more of an extension to ondra's answer
When using truncate() ( my preferred method ) make sure your cursor is at the required position.
When a new file is opened for reading - open('FILE_NAME','r') it's cursor is at 0 by default.
But if you have parsed the file within your code, make sure to point at the beginning of the file again i.e truncate(0)
By default truncate() truncates the contents of a file starting from the current cusror position.
A simple example

As #jamylak suggested, a good alternative that includes the benefits of context managers is:
with open('filename.txt', 'w'):
pass

When using with open("myfile.txt", "r+") as my_file:, I get strange zeros in myfile.txt, especially since I am reading the file first. For it to work, I had to first change the pointer of my_file to the beginning of the file with my_file.seek(0). Then I could do my_file.truncate() to clear the file.

Writing and Reading file content
def writeTempFile(text = None):
filePath = "/temp/file1.txt"
if not text: # If not provided return file content
f = open(filePath, "r")
slug = f.read()
return slug
else:
f = open(filePath, "a") # Create a blank file
f.seek(0) # sets point at the beginning of the file
f.truncate() # Clear previous content
f.write(text) # Write file
f.close() # Close file
return text
It Worked for me

If security is important to you then opening the file for writing and closing it again will not be enough. At least some of the information will still be on the storage device and could be found, for example, by using a disc recovery utility.
Suppose, for example, the file you're erasing contains production passwords and needs to be deleted immediately after the present operation is complete.
Zero-filling the file once you've finished using it helps ensure the sensitive information is destroyed.
On a recent project we used the following code, which works well for small text files. It overwrites the existing contents with lines of zeros.
import os
def destroy_password_file(password_filename):
with open(password_filename) as password_file:
text = password_file.read()
lentext = len(text)
zero_fill_line_length = 40
zero_fill = ['0' * zero_fill_line_length
for _
in range(lentext // zero_fill_line_length + 1)]
zero_fill = os.linesep.join(zero_fill)
with open(password_filename, 'w') as password_file:
password_file.write(zero_fill)
Note that zero-filling will not guarantee your security. If you're really concerned, you'd be best to zero-fill and use a specialist utility like File Shredder or CCleaner to wipe clean the 'empty' space on your drive.

You have to overwrite the file. In C++:
#include <fstream>
std::ofstream("test.txt", std::ios::out).close();

You can also use this (based on a few of the above answers):
file = open('filename.txt', 'w')
file.close()
of course this is a really bad way to clear a file because it requires so many lines of code, but I just wrote this to show you that it can be done in this method too.
happy coding!

You cannot "erase" from a file in-place unless you need to erase the end. Either be content with an overwrite of an "empty" value, or read the parts of the file you care about and write it to another file.

Assigning the file pointer to null inside your program will just get rid of that reference to the file. The file's still there. I think the remove() function in the c stdio.h is what you're looking for there. Not sure about Python.

Since text files are sequential, you can't directly erase data on them. Your options are:
The most common way is to create a new file. Read from the original file and write everything on the new file, except the part you want to erase. When all the file has been written, delete the old file and rename the new file so it has the original name.
You can also truncate and rewrite the entire file from the point you want to change onwards. Seek to point you want to change, and read the rest of file to memory. Seek back to the same point, truncate the file, and write back the contents without the part you want to erase.
Another simple option is to overwrite the data with another data of same length. For that, seek to the exact position and write the new data. The limitation is that it must have exact same length.
Look at the seek/truncate function/method to implement any of the ideas above. Both Python and C have those functions.

This is my method:
open the file using r+ mode
read current data from the file using file.read()
move the pointer to the first line using file.seek(0)
remove old data from the file using file.truncate(0)
write new content and then content that we saved using file.read()
So full code will look like this:
with open(file_name, 'r+') as file:
old_data = file.read()
file.seek(0)
file.truncate(0)
file.write('my new content\n')
file.write(old_data)
Because we are using with open, file will automatically close.