Why are non-Western countries siding with China in the UN? Use this method when you need to check whether the file exists or not before performing an action on the file. Not exactly, but not too far. To set the pointer to the end of a file you can use seek(0, 2), this means set the pointer to position 0 relative to the end of the file (0 = absolute positioning, 1 = relative to the start of the file, 2 = relative to the end of the file). Common exceptions when you are working with files include. os.path.isdir () method in Python is used to check whether the specified path is an existing directory or not. Lets use this function to check if any process with chrome substring in name is running or not i.e. Read/Write data. This application cannot be modified. Here is a generator that iterates over files in use for a specific PID: On Windows it is not quite so straightforward, the APIs are not published. Python - How to check if a file is used by another application? For this example, we'll measure the initial size of the file, wait 2 seconds, then measure it again and compare the two sizes to see if it changed. This solution only can be used for Linux system. Unless both the new application and the legacy application need synchronized access for writing to the same file and you are willing to handle the possibility of the legacy application being denied opening of the file, do not use this method. How can I access environment variables in Python? The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network. During her writing stints, she has been associated with digital marketing agencies and technical firms. To compare all files within a directory, all you need to do is create a function to iterate over the contents of a folder, creating a hash or measuring its size and storing that result in a dictionary, if the item you are iterating over is a sub-directory, we can recursively call the same function. How to work with context managers and why they are useful. The issue with this method is that for larger files it can take quite some time and processing power to calculate a checksum of the file. You can work with this list in your program by assigning it to a variable or using it in a loop: We can also iterate over f directly (the file object) in a loop: Those are the main methods used to read file objects. If favouring the "check whether the legacy application has the file open" (intrusive approach prone to race conditions) then you can solve the said race condition by: Updated NOTE on this solution: Checking with FileAccess.ReadWrite will fail for Read-Only files so the solution has been modified to check with FileAccess.Read. The system will not allow you to open the file under these circumstances. This is the file now, after running the script: Tip: The new line might not be displayed in the file until f.close() runs. There are 10 files in the folder. Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? With lsof we can basically check for the processes that are using this particular file. Connect and share knowledge within a single location that is structured and easy to search. How do I tell if a file does not exist in Bash? If we're able to rename it, then no other process is using it. The legacy application is opening and closing the file every X minutes, but I do not want to assume that at t = t_0 + n*X + eps it already closed the file. In contrast, readlines() returns a list with all the lines of the file as individual elements (strings). This is my current working directory: With this mode, you can create a file and then write to it dynamically using methods that you will learn in just a few moments. To get quick access to Python IDE, do check out Replit. rev2023.3.1.43269. The first method that you need to learn about is read(), which returns the entire content of the file as a string. Required fields are marked *. I can still open a file which is opend with 'w+' by another process. The test commands only work in Unix based machines and not Windows based OS machines. Does Cosmic Background radiation transmit heat? "TypeError: a bytes-like object is required, not 'str'" when handling file content in Python 3. You can use this function to check if a file is in used. You can create, read, write, and delete files using Python. To provide the best experiences, we use technologies like cookies to store and/or access device information. This is not a bad solution if you have few users for the fileit is indeed a sort of locking mechanism on a private file. The first parameter of the open() function is file, the absolute or relative path to the file that you are trying to work with. Get started, freeCodeCamp is a donor-supported tax-exempt 501(c)(3) charity organization (United States Federal Tax Identification Number: 82-0779546). Does With(NoLock) help with query performance? An easy way to lock a file in a cross-platform way is to avoid the system call and cheat. Replies have been disabled for this discussion. The log file will be rollovered in certain interval. Python 3.4 and above versions offer the Pathlib module, which can be imported using the import function. How to check if a file is open for writing on windows in python? In my app, I write to an excel file. Very nice solution. At a minimum you should pair the two rename operations together. The following code returns a list of PIDs, in case the file is still opened/used by a process (including your own, if you have an open handle on the file): I provided one solution. Tip: A module is a Python file with related variables, functions, and classes. A better solution is to open the file in read-only mode and calculate the file's size. the try statement is being ignored on my end. And have some results: I tried this code, but it doesn't work, no matter i use "r+" or "a+" flag. How to troubleshoot crashes detected by Google Play Store for Flutter app, Cupertino DateTime picker interfering with scroll behaviour. Join Bytes to post your question to a community of 471,987 software developers and data experts. Python has a built-in module OS which can be called upon to interact with the underlying files, folders and directories. 2. Then it takes the return value of the code. The first step is to import the built-in function using the import os.path library. Tip: You can get the same list with list(f). To see if anything has changed in the directory, all you need to do is compare the output of this function over a given interval just as we did in the first two examples. You can change your settings at any time, including withdrawing your consent, by using the toggles on the Cookie Policy, or by clicking on the manage consent button at the bottom of the screen. An issue with trying to find out if a file is being used by another process is the possibility of a race condition. To be able to read a file and perform another operation in the same program, you need to add the "+" symbol to the mode, like this: Very useful, right? I do not want to assume that at t = @twinaholic: Probably not, but the program would continue running even if the file couldn't be opened. Is the legacy application opening and closing the file between writes, or does it keep it open? In Python, there are several ways to check if a file exists; here are the top methods you should know about. Using os.path.isdir () Method to check if file exists. I want to build an application on top of an existing one. I need this on FreeBSD. The value returned is limited to this number of bytes: Important: You need to close a file after the task has been completed to free the resources associated to the file. Notice that we are writing data/ first (the name of the folder followed by a /) and then names.txt (the name of the file with the extension). If the file is in use, then the other process (assuming it isn't your application that is holding it - if you get this with every file, then it may be) has an exclusive lock on the file. I write in Perl. Thanks, I had tried comparing size, modification times, etc, and none of that worked. Learn how your comment data is processed. This code can work, but it can not reach my request, since i don't want to delete the file to check if it is open. Sometimes, you may want to delete the content of a file and replace it entirely with new content. You could check a file, decide that it is not in use, then just before you open it another process (or thread) leaps in and grabs it (or even deletes it). The only other option I could think of was to try and rename the file or directory containing the file temporarily, then rename it back. Ok, let's say you decide to live with that possibility and hope it does not occur. This is a huge advantage during the process of debugging. All Rights Reserved. Context Managers are Python constructs that will make your life much easier. Share. Could you supply me with some python code to do this task? How do I include a JavaScript file in another JavaScript file? If used it must be a byte sequence, or a string if encoding or errors is specified or text is true. sharing (locking): this assumes that the legacy program also opens the file in shared mode (usually the default in Windows apps); moreover, if your application acquires the lock just as the legacy application is attempting the same (race condition), the legacy application will fail. t_0 + n*X + eps it already closed If the size differs during the two intervals, you know there has been a modification made to the file. So, we will iterate over all the running process and for each process whose name contains the given string, we will keep it's info in a list i.e. To learn more about them, please read this article in the documentation. As in my system many chrome instances are running. It works well for me on linux, how about windows? Vim seems to use. I can just parse the output of lsof for the file I need before accessing it. This is basically telling us that a file object is an object that lets us work and interact with existing files in our Python program. please see the following code. Much rather have his message and yours than neither. file for that process. If no options are specified, fstat reports on all open files in the system. 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Save process output (stdout) We can get the output of a program and store it in a string directly using check_output. How do I check whether a file exists without exceptions? This can be used when the file that you are trying to open is in the same directory or folder as the Python script, like this: But if the file is within a nested folder, like this: Then we need to use a specific path to tell the function that the file is within another folder. this is extremely intrusive and error prone. You can watch for file close events, indicating that a roll-over has happened. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. But if the user forgets to close the file before any further writing, a warning message should appear. If all you care about is the current process, an easy way is to use the file object attribute "closed". Close the file to free the resouces. One thing I've done is have python very temporarily rename the file. What factors changed the Ukrainians' belief in the possibility of a full-scale invasion between Dec 2021 and Feb 2022? "How to Handle Exceptions in Python: A Detailed Visual Introduction". A file is considered open by a edit: I'll try and clarify. Acceleration without force in rotational motion? Pre-requisites: Ensure you have the latest Python version installed. A curious thing is that if you try to run this line again and a file with that name already exists, you will see this error: According to the Python Documentation, this exception (runtime error) is: Now that you know how to create a file, let's see how you can modify it. Why was the nose gear of Concorde located so far aft? Whether there is a pythonic or non-pythonic way of doing this will probably be the least of your concerns - the hard question will be whether what you are trying to achieve will be possible at all. What factors changed the Ukrainians' belief in the possibility of a full-scale invasion between Dec 2021 and Feb 2022? Asking for help, clarification, or responding to other answers. If the user interrupts the program (ctrl-c) after the first rename then the filename will not be restored and the user will be unaware of this condition. You'd still be in trouble even if python would let you write something like: if file_is_open(filename): process_file(filename) There's nothing that says no one will open the file after the file_is_open call but before the process_file call. As per the existence of the file, the output will display whether or not the file exists in the specified path. For example, if you only need to read the content of a file, it can be dangerous to allow your program to modify it unexpectedly, which could potentially introduce bugs. As a programmer, you need to foresee these circumstances and handle them in your program to avoid sudden crashes that could definitely affect the user experience. What is behind Duke's ear when he looks back at Paul right before applying seal to accept emperor's request to rule? Since glob is used for pattern matching, you can use it to check a files status. Whether there is a pythonic or non-pythonic way of doing this will probably be the least of your concerns - the hard question will be whether what you are trying to achieve will be possible at all. Torsion-free virtually free-by-cyclic groups. Why is there a memory leak in this C++ program and how to solve it, given the constraints? However, this method will not return any files existing in subfolders. Check If a File Is Not Open Nor Being Used by Another Process. In such a situation, you'll first want to check that this is not the case, wait if necessary and the only proceed with accessing the necessary file. If you are working with files that are larger than just a few megabytes, you could run in to issues such as high CPU usage, long wait times or running out of memory entirely. You could check a file, decide that it is not in use, then just before you open it another process (or thread) leaps in and grabs it (or even deletes it). Familiarity with any Python-supported text editor of your choice. Is there a way to check if a file with given name is opened by some process (other than our process)? I really hope you liked my article and found it helpful. In her free time, she likes to paint, spend time with her family and travel to the mountains, whenever possible. To generate an MD5 checksum of a file, we can make use of the. "Appending" means adding something to the end of another thing. "Education is the most powerful weapon which you can use to change the world." Nelson Mandela Contents [ hide] 1. Can you check for Windows File-type Association, way to check values before Initialisation. Linux is a registered trademark of Linus Torvalds. Throw an error when writing to a CSV file if file is in-use in python? Is lock-free synchronization always superior to synchronization using locks? You can do this with the write() method if you open the file with the "w" mode. Now that you can accurately determine the size of a file at a given point, you'll need to create a piece of code that measures a file's size at two different intervals. Let's see what happens if we try to do this with the modes that you have learned so far: If you open a file in "r" mode (read), and then try to write to it: Similarly, if you open a file in "w" mode (write), and then try to read it: The same will occur with the "a" (append) mode. Whether those other application read/write is irrelevant for now. Ackermann Function without Recursion or Stack. In this example we create a function that generates an MD5 hash from the contents of a given file. Would you check the link of lsof? For checking the existence of a file(s), you can use any of the procedures listed above. Every developer understands the need to create fall back codes, which can save a prorgram from failing in the case that a condition isn't met. rev2023.3.1.43269. Is there a pythonic way to do this? This argument is provided since some operating systems permit : in a file name.-d or --diff <file1> <file2> Open a file difference editor. How do I concatenate two lists in Python? This context manager opens the names.txt file for read/write operations and assigns that file object to the variable f. This variable is used in the body of the context manager to refer to the file object. This is how you could do that: #. Learn how to detect whether a given file is being copied or currently being modified/written to using pure Python. So I need a way to check this file is open before the writing process. This minimizes the window of danger. The test command in the sub-process module is an efficient way of testing the existence of files and directories. And we want to add a new line to it, we can open it using the "a" mode (append) and then, call the write() method, passing the content that we want to append as argument. If you do want to detect modifications to larger files in this manner, consider making use of the update() function to feed your file in chunks to the MD5 function, this is more memory efficient. Tip: The default modes are read ("r") and text ("t"), which means "open for reading text" ("rt"), so you don't need to specify them in open() if you want to use them because they are assigned by default. The '-f' function tests the existence of a file and returns False for a directory. the given string processName. Amending it to be an answer, with a comment about what to avoid would make sense. The try and except statement checks a command and produces an output. Each string represents a line to be added to the file. That solves the problems brought up in the comments to his answer. @DennisLi Same happened to me. :). See something you don't agree with or feel could be improved? But wait! If Pythons processor is able to locate the file, it will open the file and print the result File is open and available for use. This is posted as an answer, which it is not. open ("demo.txt") Not completely safe without a lock, but I can handle correctness only in 99.99% of the cases. This is exactly what I needed, and works as intended if you are doing a file operation, e.g scraping from the web then writing to a file and want to know when it's completed to either carry on operations or to display 'done' to the user. # retrieve the current position of the pointer, # if the function reaches this statement it means an error occurred within the above context handler, # if the initial size is equal to the final size, the file has most likely. Understand your hesitation about using exceptions, but you can't avoid them all of the time: Ok after talking to a colleague and a bit of brainstorming I came up with a better solution. The glob module matches all the pathnames with the specified parameters and succinctly allows you to access the file system. import psutil for proc in psutil.process_iter (): try: # this returns the list of opened files by the current process flist = proc.open_files () if flist: print (proc.pid,proc.name) for nt in flist: print ("\t",nt.path) # This catches a race condition where a process ends # before we can examine its files except psutil.NoSuchProcess as err: print #, Mar 7 '07 You can use the type() function to confirm that the value returned by f.read() is a string: In this case, the entire file was printed because we did not specify a maximum number of bytes, but we can do this as well. How to create an empty NumPy Array in Python? The second parameter of the open() function is the mode, a string with one character. It doesn't work. Here you can see an example with FileNotFoundError: Tip: You can choose how to handle the situation by writing the appropriate code in the except block. If check is true, and the process exits with a non-zero exit code, a CalledProcessError exception will be raised. To remove a file using Python, you need to import a module called os which contains functions that interact with your operating system. The output is True, since the folder/directory exists at the specified path. There has one thread will regularly record some logs in file. Get a list of all the PIDs of a all the running process whose name contains. Connect and share knowledge within a single location that is structured and easy to search. PTIJ Should we be afraid of Artificial Intelligence? in code side, the pseudocode similars like below: So, how do i check is a file is already open or is used by other process? The "a" mode allows you to open a file to append some content to it. import os.path os.path.isfile (r "C:\Users\Wini Bhalla\Desktop\Python test file.txt") How to choose voltage value of capacitors. Learn more, Capturing Output From an External Program. If you try to do so, you will see this error: This particular exception is raised when you try to open or work on a directory instead of a file, so be really careful with the path that you pass as argument. Why do we kill some animals but not others? The only difference here is that this command only works for directories. How to create a file in memory for user to download, but not through server? Thanks for your answers. It really makes sense for Python to grant only certain permissions based what you are planning to do with the file, right? Here's the code: You can check if a file has a handle on it using the next function (remember to pass the full path to that file): I know I'm late to the party but I also had this problem and I used the lsof command to solve it (which I think is new from the approaches mentioned above). Agree with or feel could be improved certain permissions based what you are planning to do the. Temporarily rename the file, the output will display whether or not the file attribute! For file close events, indicating that a roll-over has happened Python version installed False for a directory close.: you can use any of the code the same list with the... Superior to synchronization using locks our terms of service, privacy policy and cookie policy write an! Hash from the contents of a full-scale invasion between Dec 2021 and 2022. It really makes sense for Python to grant only certain permissions based what you are working with files include you. Python: a bytes-like object is required, not 'str ' '' when handling file content in 3! A '' mode and none of that worked ; here are the top methods you know! Readlines ( ) method in Python code to do with the write )... Output is true, since the folder/directory exists at the specified path community of 471,987 developers. Using check_output I 've done is have Python very temporarily rename the file object attribute `` closed.! The write ( ) method if you open the file under these circumstances string represents a line to be to! The constraints detect whether a file is in used the running process whose name contains access the file.... Open files in the possibility of a file with related variables, functions, delete! Be added to the end of another thing to an excel file time with her family and travel the! Siding with China in the possibility of a program and store it in a way. The return value of the code be added to the file I a! More about them, please read this article in the sub-process module a... Or currently being modified/written to using pure Python latest Python version installed access to Python IDE, do check Replit... Back at Paul right before applying seal to accept emperor 's request to?. Solves the problems brought up in the specified parameters and succinctly allows you to access the file.. You care about is the Dragonborn 's Breath Weapon from Fizban 's of! Mode, a string if encoding or errors is specified or text is true if you the... Generate an MD5 checksum of a given file the contents of a program and store in... Sub-Process module is a huge advantage during the process exits with a non-zero code! That is structured and easy to search CSV file if file is in-use in:. A comment about what to avoid the python check if file is open by another process will not return any files existing in subfolders options specified! Function tests the existence of files and directories the user forgets to close the file in read-only and. Some content to it these circumstances files, folders and directories may want to build an application on of. An issue with trying to find out if a file in another JavaScript file of debugging with family... Not others you supply me with some Python code to do this with the `` a '' mode difference... Python 3 be raised rather have his message and yours than neither service... ' '' when handling file content in Python, you may want to build an application on top of existing... Variables, functions, and none of that worked your choice the try is. Be used for Linux system except statement checks a command and produces an output the code only works for.... Each string represents a line to be an answer, you need to if... With trying to find out if a file with related variables, functions, and process. Are specified, fstat reports on all open files in the possibility of a the. Write ( ) returns a list of all the PIDs of a file is in.... Chrome instances are running knowledge within a single location that is structured and easy search. Contains functions that interact with the write ( ) returns a list with all the pathnames the. Detected by Google Play store for Flutter app, I had tried comparing size, modification times, etc and. Need before accessing it given name is running or not there has one thread will regularly record some logs file... Technical firms find out if a file and returns False for a directory string with one.... An application on top of an existing directory or not before performing an action on file! I really hope you liked my article and found it helpful way of testing the existence a... Could you supply me with some Python code to do with the specified.... Opened by some process ( other than our process ) OS which be... Flutter app, I had tried comparing size, modification times, etc, and none of worked. Used to check values before Initialisation module is an efficient way of testing the existence of the open a! N'T agree with or feel could be improved in name is running or not file... Output from an External program os.path library the Dragonborn 's Breath Weapon from Fizban 's Treasury of an... Used for Linux system File-type Association, way to check this file is before. And directories for pattern matching, you need to check if a file exists not! Use of the code, she likes to paint, spend time with her family and travel to file. Procedures listed above an empty NumPy Array in Python the processes that are using this file! A bytes-like object is required, not 'str ' '' when handling file content in Python is used another! Have the latest Python version installed avoid the system call and cheat her writing stints, she likes to,! Function is the current process, an easy way to check if a file is being or... Version installed current process, an easy way to check whether a given file is being copied or currently modified/written! And travel to the file, right a files status and easy to search this C++ and! Memory for user to download, but not through server statement is being by! ( other than our process ) two rename operations together use any the... Pattern matching, you can create, read, write, and delete using. Python 3: I 'll try and except statement checks a command and produces an.! Underlying files, folders and directories only difference here is that this command works... You liked my article and found it helpful: Ensure you have the latest Python version.! A function that generates an MD5 hash from the contents of a file we. 471,987 software developers and data experts a given file first step is to use the file individual. Download, but not through server done is have Python very temporarily rename file! It helpful another thing animals but not through server an error when writing to CSV. In certain python check if file is open by another process 've done is have Python very temporarily rename the file system, way to a. Read-Only mode and calculate the file, we can make use of the file object attribute `` ''... Not allow you to open the file exists or not before performing action. Responding to other answers brought up in the possibility of a file is in used for... Spend time with her family and travel to the mountains, whenever possible, read, write, the. Nor being used by another process agree to our terms of service privacy... Or text is true, since the folder/directory exists at the specified path my! Returns a list of all the running process whose name contains to append some content to.... It helpful write ( ) method to check whether a given file the processes that are using this file. Performing an action on the file system forgets to close the file in a string one! Can watch for file close events, indicating that a roll-over has happened to! Array in Python, there are several ways to check if a file to append content... Posted as an answer, you can do this task the log file will raised. To accept emperor 's request to rule through server OS machines the documentation me with some code. Individual elements ( strings ) `` TypeError: a bytes-like object is required, not 'str ''! Instances are running data experts message and yours than neither this function to check a. Size, modification times, etc, and none of that worked, way to check if a file Python. Whether a given file it works well for me on Linux, how Windows. Method in python check if file is open by another process, you agree to our terms of service, privacy policy cookie! Are specified, fstat reports on all open files in the possibility of a file is considered by. Be called upon to interact with the specified parameters and succinctly allows you access! Given the python check if file is open by another process huge advantage during the process of debugging been associated with digital marketing and! Content to it if file exists ; here are the top methods you should the. To synchronization using locks an issue with trying to find out if a file in memory for user download. Based machines and not Windows based OS machines and returns False for a.. Then no other process is using it open ( ) method to check if any process chrome... Know about the mode, a warning message should appear accept emperor request! With your operating system before performing an action on the file, right access the 's...