Develop Reference

How to create a program that writes a print("hello world"), in the main file where the original program was written?

If I want to run a program that writes a print("hello world") in the code of my main file, where I wrote the original program, how would I do that in Python?
I thought something like:
import main
with open("main.py " , "a+") as file_object:
file_object.seek(0)
data = file_object.read(100)
if len(data)>0:
file_object.write("\n")
file_object.write('print("hello world)')
but the console shows this:
ValueError: I/O operation on closed file.

From my understanding, you are trying to determine if a file has content and if it does include a new line, and then append the print statement.
You do not need to use seek you can just check the size of the file:
import os
if os.path.getsize(filename):
# file isn't empty
else:
# file is empty
You should also close the quotation marks in your print statement

You can use __file__ which gives you the path of your file and then append your text to it.
path = __file__
f = open(path, "a")
f.write('\nprint("hello world")')
f.close()

you wrong because Indent correctly, like this. You can modify like:
import main
with open("main.py" , "a+") as file_object:
file_object.seek(0)
data = file_object.read(100)
if len(data)>0:
file_object.write("\n")
file_object.write('print("hello world")')

Python results output to txt file

I tried this code posted 2 years ago:
import subprocess
with open("output.txt", "wb") as f:
subprocess.check_call(["python", "file.py"], stdout=f)
import sys
import os.path
orig = sys.stdout
with open(os.path.join("dir", "output.txt"), "wb") as f:
sys.stdout = f
try:
execfile("file.py", {})
finally:
sys.stdout = orig
It hangs up the terminal until I ctl-z and then it crashes the terminal but prints the output.
I'm new to coding and am not sure how to resolve. I'm obviously doing something wrong. Thanks for your help.

You can simply open and write to the file with write.
with open('output.txt', 'w') as f:
f.write('output text') # You can use a variable from other data you collect instead if you would like
Since you are new to coding, i'll just let you know that opening a file using with will actually close it automatically after the indented code is ran. Good luck with your project!

Casper.js unable to open JSON file when activated through python script

I have a CasperJS script that opens a JSON file of search terms and parses a page looking for them. It works fine when I run it from the command line.
var casper = require('casper').create();
var fs = require('fs')
var names = fs.read('/var/www/html/tracker/names.json');
...
But when I try to run it through a shell script using Python, it has difficulty reading the JSON file. fs.read returns "".
The Python script:
app = subprocess.Popen("/usr/local/bin/casperjs /var/www/html/tracker/scraper.js", shell=True)
app.wait()
out, errs = app.communicate()

Figured it out. Naturally, my own boneheaded mistake.
Didn't make this clear in the question, but the Python script first prepares names.json before running the scraper through a subprocess. So if we add a little bit to the code snippet shown above:
# Save JSON file
f = open('names.json', 'w')
f.write( json.dumps(json_ready, sort_keys=True, indent=4) )
# Query scraper
app = subprocess.Popen("/usr/local/bin/casperjs /var/www/html/tracker/scraper.js", shell=True)
app.wait()
out, errs = app.communicate()
The problem? I forgot to close f.
# Save JSON file
f = open('names.json', 'w')
f.write( json.dumps(json_ready, sort_keys=True, indent=4) )
f.close()

How to execute a python script and write output to txt file?

I'm executing a .py file, which spits out a give string. This command works fine
execfile ('file.py')
But I want the output (in addition to it being shown in the shell) written into a text file.
I tried this, but it's not working :(
execfile ('file.py') > ('output.txt')
All I get is this:
tugsjs6555
False
I guess "False" is referring to the output file not being successfully written :(
Thanks for your help

what your doing is checking the output of execfile('file.py') against the string 'output.txt'
you can do what you want to do with subprocess
#!/usr/bin/env python
import subprocess
with open("output.txt", "w+") as output:
subprocess.call(["python", "./script.py"], stdout=output);

This'll also work, due to directing standard out to the file output.txt before executing "file.py":
import sys
orig = sys.stdout
with open("output.txt", "wb") as f:
sys.stdout = f
try:
execfile("file.py", {})
finally:
sys.stdout = orig
Alternatively, execute the script in a subprocess:
import subprocess
with open("output.txt", "wb") as f:
subprocess.check_call(["python", "file.py"], stdout=f)
If you want to write to a directory, assuming you wish to hardcode the directory path:
import sys
import os.path
orig = sys.stdout
with open(os.path.join("dir", "output.txt"), "wb") as f:
sys.stdout = f
try:
execfile("file.py", {})
finally:
sys.stdout = orig

If you are running the file on Windows command prompt:
python filename.py >> textfile.txt
The output would be redirected to the textfile.txt in the same folder where the filename.py file is stored.
The above is only if you have the results showing on cmd and you want to see the entire result without it being truncated.

The simplest way to run a script and get the output to a text file is by typing the below in the terminal:
PCname:~/Path/WorkFolderName$ python scriptname.py>output.txt
*Make sure you have created output.txt in the work folder before executing the command.

Use this instead:
text_file = open('output.txt', 'w')
text_file.write('my string i want to put in file')
text_file.close()
Put it into your main file and go ahead and run it. Replace the string in the 2nd line with your string or a variable containing the string you want to output. If you have further questions post below.

file_open = open("test1.txt", "r")
file_output = open("output.txt", "w")
for line in file_open:
print ("%s"%(line), file=file_output)
file_open.close()
file_output.close()

using some hints from Remolten in the above posts and some other links I have written the following:
from os import listdir
from os.path import isfile, join
folderpath = "/Users/nupadhy/Downloads"
filenames = [A for A in listdir(folderpath) if isfile(join(folderpath,A))]
newlistfiles = ("\n".join(filenames))
OuttxtFile = open('listallfiles.txt', 'w')
OuttxtFile.write(newlistfiles)
OuttxtFile.close()
The code above is to list all files in my download folder. It saves the output to the output to listallfiles.txt. If the file is not there it will create and replace it with a new every time to run this code. Only thing you need to be mindful of is that it will create the output file in the folder where your py script is saved. See how you go, hope it helps.

You could also do this by going to the path of the folder you have the python script saved at with cmd, then do the name.py > filename.txt
It worked for me on windows 10

Read file and copy to standard output.

I'm trying to write a python program that will read input and copy it to standard output (with no alterations). I've been told that it needs to operate as a Python version of the Unix cat function. If a file cannot be opened, an error message needs to be printed, and then the program needs to continue processing any additional files. I am a complete beginner, and have tried my best to scrape something together with my limited knowledge. Here is what I have so far:
from sys import argv, stdout, stdin, stderr
if len(argv) == 1:
try:
stdout.write(raw_input(' ') + '\n')
except:
stderr.write ('sorry' + '\n')
quit()
else:
for filename in argv[1:]:
try:
filehandle + open(filename)
except IOError:
stderr.write('Sorry, could not open', filename + '\n')
continue
f = filehandle.read()
stdout.write(f)
I am not quite sure where to go from here.. does anyone have any advice/am I on the right track even a little bit? Please and thank you!

This function will copy the specified file to the console line by line (in case you later on decide to give it the ability to use the -n command line option of cat)
def catfile(fn):
with open(fn) as f:
for line in f:
print line,
It can be called with the filename once you have established the file exists.