How to check whether a file exists in Python

Key Takeaways

how should you check whether or not a file or directory exists in Python this is one of those things that's confusing mostly because python offers several different ways to do it so which one should you use I've seen many beginners follow a path like this first they check to see if the path exists using something like os. path. exists print something in return if it doesn't and then proceed to open the file and do something with the data if it does and in most situations although this does have some problems let's be honest it's probably fine for small personal scripts and other things like that I probably wouldn't even worry about it but if your intention is to build something just a little bit more robust then let's take a look at some of the issues the first issue is that time passes between when we check to see if the file exists and when we try to open it it's possible that another thread or some external process deleted the file between when we check whether it exists and when we tried to open it if that were to happen this open call would raise an exception specifically a F not found error which is something you might like to catch so really we need to basically repeat our error handling code okay so we surround it in a try accept but wait if open was going to throw if the file didn't exist then why did we need to check that it exists in the first place and that's my point checking whether it exists or not is basically redundant if you're going to open the file immediately after checking whether it exists instead just try to open it it either exists and opened successfully or you get an exception when you do it this way the operating system will prevent other processes from deleting the file out from under you as long as you have it open in Python although it typically will not prevent the same process from deleting it out from under itself it's also still possible that other threads or processes read or write to the file in between when you open it and when you read it so there are still things you need to worry about just a few less of them another advantage of this approach is that there are other things that can go wrong when you try to open a file besides the file not being found for instance you might get an is a directory error if you tried to open a directory instead of a file you could use the OS path function to check if something's a directory but once again you'd end up with a potential very subtle bug if whether it's a directory not changes in between when you ask the question and when you actually try to open the file so if you're checking whether the file exists because you want to open it then don't just try to open it and catch whatever errors you get and if you want to be super modern you even consider using path Li read text as a quick oneliner to get all the data out but sometimes you don't want to actually open the file you really do just want to know whether or not it exists you could be using the existence of a file as a Boolean checking whether an old temp file exists or checking if the user made a configuration directory in that case the recommended way to check whether or not a file or directory exists depends on whether you really need strings or whether you could do with pathlib path objects many applications default to Strings because it seems like the easiest choice and in a lot of cases it is if that's you then OS path exists might be what you want hopefully unsurprisingly it tells you whether or not the file exists exist will return true for files and directories and it also follows symbolic links in particular exists will return false For a symbolic link that points to a file that doesn't exist so even if there is an actual file the symbolic link at this location it would still return false it does sound a bit confusing but this is the behavior that you would usually want if you want to check that you got an actual file and not a directory or some kind of device object then you want is file instead once again is file follows links and this is probably what you want even though it sounds a little confusing and you guessed it for directories there's iser and it also follows symbolic links so that's all fine and dandy and it works but using strings to represent paths can be kind of error prone instead using path lb. path can provide a more ergonomic and safer interface if you already have a string you can convert to a path very easily like this or you can do it like this if you're constructing from scratch paths provide a wrapper around a lot of the os. paath functionality and they make it easy to access through method calls for instance path. exists we'll use os. path. exists path. is file we'll use os. paath do is file and similarly for isur and number of other os. paath functions if you're already using strings all over the place of course there's a bit of overhead to convert but once you do pretty much every built-in function that takes a string path also takes a pathlib path and importantly path. path takes care of a lot of idiosyncrasies that might come up if you were to switch operating systems things like using forward slashes on Linux but backs slashes on Windows oh and pathlib actually follows pep eight