Develop Reference

Writing variables to new line of txt file in python

From other posts, I've learned that '\n' signifies a new line when adding to a txt file. I'm trying to do just this, but I can't figure out the right syntax when an attribute is right before the new line.
My code I'm trying is like this:
for item in list:
with open("file.txt", "w") as att_file:
att_file.write(variable\n)
As you can probably see, I'm trying to add the variable for each item in the list to a new line in a txt file. What's the correct way to do this?

You just need to specify the newline character as a string:
Eg:
with open("file.txt", "w") as att_file:
for item in list:
att_file.write(attribute + "\n")

try this:
att_file.write(attribute+"\n")
note :attribute must be some variable and must be string type
your code will look like this:
with open("file.txt", "w") as att_file:
for item in list:
att_file.write(item+"\n")
with should be before for, else every time you are opening file with write mode, it will omit the
previous write

file7 = open('test_list7_file.txt','a')
file7.write(var7 + '\n')
will work fine, BUT IF YOU APPEND TO EXISTING txt file the MOUSE CURSOR
needs to be ONE SPACE AFTER THE LAST ENTRY when you save the file for use in your program.
~no space and it joins the last entry,
~on the next line already when you create you file to be added to, it adds an empty line first

Python does not read file contents in a+ mode. Reads new line character as a separate line between two consecutive lines

I have the following code
checkIP = open("checkIP.txt", "r+")
ip = '10.xx.xx.xxx'
checkIP.write(ip)
The problem is let say when I write variable ip for first time. It gets added to the file.
Second time when I run the program variable ip is added to file so the file now looks like this.
10.xx.xx.xxx10.xx.xx.xxx
If instead I have checkIP.write( ip + '\n'), when i run second time the file looks like
10.xx.xx.xxx
10.xx.xx.xxx
But when I run it third time line by line it reads 10.xx.xx.xxx as first line ,'\n' as second and 10.xx.xx.xxx as third.
Also if I have a+ as the mode and after first time I have
10.xx.xx.xxx
It just reads nothing from file. There is no blank or new line present.
What I want to do is everytime I add an IP it should append in next line and everytime I read there should not be any new line character when I read line by line in python.
Any help would be appreciated.

with open("someText.txt","a+") as f:
f.writeline(new_ip_address)
ip_addresses = map(str.strip,open("someText.txt"))
Im not really sure what your question actually is ... but this will do what you asked for

edit a file line by line interactively from user input in python

I want to know how to edit a file on the fly row by row in python.
For example I have a text file where I usually have:
key value
key value
key value
key value
key value
...
they are not necessarily the same pair for each line. It's just the way I explained it.
I would like to show line by line key and value (on my terminal) and then I want to do one of this two things:
-just press enter (or whatever hot-key) to go ahead and read (show) next line.
-enter a new value then hit enter. this will actually replace the value (that was being shown) on the file and finally go ahead to show next pair of key values.
Till end of file or possibly till I type 'quit' or some other keyword. doesn't matter.
-Being able to go back to the previous row would be a plus (in case of accidentally going to next row), but it's not too important for now.
I find myself often editing huge files in a very tedious and repetitive way, and text editors are really frustrating with their cursors going everywhere when pressing the arrow-key. Also having to use the backspace to delete is annoying.
I know how to read a file and how to write a file in python. But not in such interactive way. I only know how to write the whole file at once. Plus I wouldn't know if it is safe to open the same file in both reading and writing. Also I know how to manipulate each line, split the text in a list of values etc... all I really need is to understand how to modify the file at that exact current line and handle well this type of interaction.
what is the best way to do this?

All the answers focus on loading the contents of the file in memory, modifying and then on close saving all on disk, so I thought I'd give it a try:
import os
sep = " "
with open("inline-t.txt", "rb+") as fd:
seekpos = fd.tell()
line = fd.readline()
while line:
print line
next = raw_input(">>> ")
if next == ":q":
break
if next:
values = line.split(sep)
newval = values[0] + sep + next + '\n'
if len(newval) == len(line):
fd.seek(seekpos)
fd.write(newval)
fd.flush()
os.fsync(fd)
else:
remaining = fd.read()
fd.seek(seekpos)
fd.write(newval + remaining)
fd.flush()
os.fsync(fd)
fd.seek(seekpos)
line = fd.readline()
seekpos = fd.tell()
line = fd.readline()
The script simply opens the file, reads line by line, and rewrites it if the user inputs a new value. If the length of the data matches previous data, seek and write are enough. If the new data is of different size, we need to clean-up after us. So the remainder of the file is read, appended to the new data, and everything is rewritten to disk. fd.flush and os.fsync(fd) guarantee that changes are indeed available in the file as soon as it is written out. Not the best solution, performance-wise, but I believe this is closer to what he asked.
Also, consider there might be a few quirks in this code, and I'm sure there's room for optimizing -- perhaps one global read at the beggining to avoid multiple whole file reads if changes that need adjusting are made often, or something like that.

The way I would go about this is to load all the lines of the text file in a list, and then iterate through that list, changing the values of the list as you go along. Then at the very end (when you get to the last line or whenever you want), you will write that whole list out to the file with the same name, so that way it will overwrite the old file.

Write strings to another file

The Problem - Update:
I could get the script to print out but had a hard time trying to figure out a way to put the stdout into a file instead of on a screen. the below script worked on printing results to the screen. I posted the solution right after this code, scroll to the [ solution ] at the bottom.
First post:
I'm using Python 2.7.3. I am trying to extract the last words of a text file after the colon (:) and write them into another txt file. So far I am able to print the results on the screen and it works perfectly, but when I try to write the results to a new file it gives me str has no attribute write/writeline. Here it the code snippet:
# the txt file I'm trying to extract last words from and write strings into a file
#Hello:there:buddy
#How:areyou:doing
#I:amFine:thanks
#thats:good:I:guess
x = raw_input("Enter the full path + file name + file extension you wish to use: ")
def ripple(x):
with open(x) as file:
for line in file:
for word in line.split():
if ':' in word:
try:
print word.split(':')[-1]
except (IndexError):
pass
ripple(x)
The code above works perfectly when printing to the screen. However I have spent hours reading Python's documentation and can't seem to find a way to have the results written to a file. I know how to open a file and write to it with writeline, readline, etc, but it doesn't seem to work with strings.
Any suggestions on how to achieve this?
PS: I didn't add the code that caused the write error, because I figured this would be easier to look at.
End of First Post
The Solution - Update:
Managed to get python to extract and save it into another file with the code below.
The Code:
inputFile = open ('c:/folder/Thefile.txt', 'r')
outputFile = open ('c:/folder/ExtractedFile.txt', 'w')
tempStore = outputFile
for line in inputFile:
for word in line.split():
if ':' in word:
splitting = word.split(':')[-1]
tempStore.writelines(splitting +'\n')
print splitting
inputFile.close()
outputFile.close()
Update:
checkout droogans code over mine, it was more efficient.

Try this:
with open('workfile', 'w') as f:
f.write(word.split(':')[-1] + '\n')
If you really want to use the print method, you can:
from __future__ import print_function
print("hi there", file=f)
according to Correct way to write line to file in Python. You should add the __future__ import if you are using python 2, if you are using python 3 it's already there.

I think your question is good, and when you're done, you should head over to code review and get your code looked at for other things I've noticed:
# the txt file I'm trying to extract last words from and write strings into a file
#Hello:there:buddy
#How:areyou:doing
#I:amFine:thanks
#thats:good:I:guess
First off, thanks for putting example file contents at the top of your question.
x = raw_input("Enter the full path + file name + file extension you wish to use: ")
I don't think this part is neccessary. You can just create a better parameter for ripple than x. I think file_loc is a pretty standard one.
def ripple(x):
with open(x) as file:
With open, you are able to mark the operation happening to the file. I also like to name my file object according to its job. In other words, with open(file_loc, 'r') as r: reminds me that r.foo is going to be my file that is being read from.
for line in file:
for word in line.split():
if ':' in word:
First off, your for word in line.split() statement does nothing but put the "Hello:there:buddy" string into a list: ["Hello:there:buddy"]. A better idea would be to pass split an argument, which does more or less what you're trying to do here. For example, "Hello:there:buddy".split(":") would output ['Hello', 'there', 'buddy'], making your search for colons an accomplished task.
try:
print word.split(':')[-1]
except (IndexError):
pass
Another advantage is that you won't need to check for an IndexError, since you'll have, at least, an empty string, which when split, comes back as an empty string. In other words, it'll write nothing for that line.
ripple(x)
For ripple(x), you would instead call ripple('/home/user/sometext.txt').
So, try looking over this, and explore code review. There's a guy named Winston who does really awesome work with Python and self-described newbies. I always pick up new tricks from that guy.
Here is my take on it, re-written out:
import os #for renaming the output file
def ripple(file_loc='/typical/location/while/developing.txt'):
outfile = "output.".join(os.path.basename(file_loc).split('.'))
with open(outfile, 'w') as w:
lines = open(file_loc, 'r').readlines() #everything is one giant list
w.write('\n'.join([line.split(':')[-1] for line in lines]))
ripple()
Try breaking this down, line by line, and changing things around. It's pretty condensed, but once you pick up comprehensions and using lists, it'll be more natural to read code this way.

You are trying to call .write() on a string object.
You either got your arguments mixed up (you'll need to call fileobject.write(yourdata), not yourdata.write(fileobject)) or you accidentally re-used the same variable for both your open destination file object and storing a string.

Python: Write to next empty line

I'm trying to write the output of something that is being done over three big iterations and each time I'm opening and closing the outfile. Counters get reset and things like this after the iterations and I'm a massive newb and would struggle to work around this with the shoddy code I've written. So even if it's slower I'd like change the way it is being output.
Currently for the output it's just rewriting over the first line so I have only the output of the last run of the program. (tau, output are variables given values in the iterations above in the code)
with open(fileName + '.autocorrelate', "w") as outfile:
outfile.writelines('{0} {1}{2}'.format(tau, output, '\n'))
I was wondering if there are any quick ways to get python to check for the first empty line when it opens a file and write the new line there?

Open with "a" instead of "w" will write at the end of the file. That's the way to not overwrite.

If you open your file in append mode : "a" instead of "w", you will be able to write a new line at the end of your file.

You do do something like that to keep a reference (line number) to every empty line in a file
# Get file contents
fd = open(file)
contents = fd.readlines()
fd.close()
empty_line = []
i = 0
# find empty line
for line in contents:
if line == "":
empty_line.append(i)
i+=1