I managed to install windows based network printer with python3 on ubuntu.
For better coding, I want to check first if the file with the drivers in it exists after the download. I know it is possible with os.path.isfile or something like that but I would like to do that with subprocess although os will not be supported in the future anymore.
So how do I do it? With subprocess.call or something like that?
to check for a file to be present, You ideally use pathlib, which is the pythonic and portable way to interact with the filesystem.
But to avoid Time of Check to Time of Use Errors (TOCTTOU) You should consider:
Instead of :
if check_printer_present():
# now, after checking the printer is present,
# the printer might go offline
use_printer()
better use:
try:
use_printer()
except PrinterError():
printer_error_cleanup()
see:
https://de.wikipedia.org/wiki/Time-of-Check-to-Time-of-Use-Problem
You might remember that idiom as :
it's better to ask forgiveness than permission
(t is better to act decisively and apologize for it later
than to seek approval to act and risk delay, objections, etc.)
Related
Basically I cant use os.Mkdir or os.MkdirAll because it will create the directories as root. I know I can go the exec.Cmd route and set the syscall.Credential{}. But thats a bit cumbersome and I have to remove and replace a lot of code.
I was wondering if there was anything global I can set so calls to the os package will be ran as a specified user.
Thanks in advance.
In general, a process will make system calls as the user that ran the process. Maybe seteuid is what you're looking for?
We have a python script that needs to trigger the open of the Microsoft Store. We believe that the easiest way to do that is to use the ms-windows-store:// protocol.
We're currently doing that like this
import subprocess
ret = subprocess.call(["start", "ms-windows-store://pdp/?ProductId=9WZDNCRFHVJL"], shell=True)
Is that the recommended way to do this? I'm not sure if using start is correct here, or if there's something better?
Use os.startfile("ms-windows-store://pdp/?ProductId=9WZDNCRFHVJL"). This calls WINAPI ShellExecuteW directly. If you use subprocess, you have the expense of starting a child process. Plus CMD's start command will first search PATH to find a file that it can execute. Presuming nothing is found (and nothing likely will be, given this name), it hands the request off to ShellExecuteExW to let the OS shell handle it.
I am currently creating a music player in python 3.3 and I have a way of opening the mp3/wav files, namely through using through 'os.startfile()', but, this way of running the files means that if I run more than one, the second cancels the first, and the third cancels the second, and so on and so forth, so I only end up running the last file. So, basically, I would like a way of reading the mp3 file length so that I can use 'time.sleep(SongLength)' between the start of each file.
Thanks in advance.
EDIT:
I forgot to mention, but I would prefer to do this using only pre-installed libraries, as i am hoping to publish this online as a part of a (much) larger program
i've managed to do this Using an external module, as after ages of trying to do it without any, i gave up and used tinytag, as it is easy to install and use.
Nothing you can do without external libraries, as far as I know. Try using pymad.
Use it like this:
import mad
SongFile = mad.MadFile("something.mp3")
SongLength = SongFile.total_time()
What I mean by this is:
I have a program. The end user is currently using it. I submit a new piece of source code and expect it to run as if it were always there?
I can't find an answer that specifically answers the point.
I'd like to be able to say, "extend" or add new features (rather than fix something that's already there on the fly) to the program without requiring a termination of the program (eg. Restart or exit).
Yes, you can definitely do that in python.
Although, it opens a security hole, so be very careful.
You can easily do this by setting up a "loader" class that can collect the source code you want it to use and then call the exec builtin function, just pass some python source code in and it will be evaluated.
Check the package
http://opensourcehacker.com/2011/11/08/sauna-reload-the-most-awesomely-named-python-package-ever/ . It allows to overcome certain raw edges of plain exec. Also it may be worth to check Dynamically reload a class definition in Python
I would like to know how to check with python, if the filename\Directory the user has supplied to me, is acceptable (not include forbidden sings and so on) by the OS (Linux, Windows, Dos) ?
I am currently using Linux, but my goal with this question is to know if there is any library that would do that automatically, in accordance to the OS's rules.
The usual approach in python is to assume everything is correct, but to catch any exceptions if you're wrong ("Easier to ask for forgiveness than permission").
So for this case, just try to do whatever you were doing with the filename, and if it's not a valid filename you can catch the exception and alert the user then.