Re: Creating a function for a directory
On Mon, 11 Nov 2013 14:26:46 -0800, Matt wrote: So I want to take the file, desktop/test.txt and write it to desktop/newfolder/test.txt. I tried the below script, and it gave me: IOError: [Errno 2] No such file or directory: 'desktop/%s.txt'. Any suggestions would be great. def firstdev(file): in_file = open(desktop/%s.txt) % file indata = in_file.read() out_file = open(desktop/newfolder/%s.txt, 'w') % file out_file.write(indata) out_file.close() in_file.close() firstdev(test) would it not be more efficient and less error prone to use the os module to copy the file rather than manually reading re-writing it (unless of- course you intend to expand this in future to process the data first)? -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
unknown wrote: On Mon, 11 Nov 2013 14:26:46 -0800, Matt wrote: So I want to take the file, desktop/test.txt and write it to desktop/newfolder/test.txt. I tried the below script, and it gave me: IOError: [Errno 2] No such file or directory: 'desktop/%s.txt'. Any suggestions would be great. def firstdev(file): in_file = open(desktop/%s.txt) % file indata = in_file.read() out_file = open(desktop/newfolder/%s.txt, 'w') % file out_file.write(indata) out_file.close() in_file.close() firstdev(test) would it not be more efficient and less error prone to use the os module to copy the file rather than manually reading re-writing it (unless of- course you intend to expand this in future to process the data first)? Hmm, I don't see a suitable function in os -- but there is shutil.copy() -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
On Tue, 12 Nov 2013 11:24:02 +0100, Peter Otten wrote: unknown wrote: On Mon, 11 Nov 2013 14:26:46 -0800, Matt wrote: So I want to take the file, desktop/test.txt and write it to desktop/newfolder/test.txt. I tried the below script, and it gave me: IOError: [Errno 2] No such file or directory: 'desktop/%s.txt'. Any suggestions would be great. def firstdev(file): in_file = open(desktop/%s.txt) % file indata = in_file.read() out_file = open(desktop/newfolder/%s.txt, 'w') % file out_file.write(indata) out_file.close() in_file.close() firstdev(test) would it not be more efficient and less error prone to use the os module to copy the file rather than manually reading re-writing it (unless of- course you intend to expand this in future to process the data first)? Hmm, I don't see a suitable function in os -- but there is shutil.copy() that's what i get for posting on the fly without checking first but i think the principle holds. -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
On 2013-11-12, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: Using os.path.exists before opening a file is, for the most part, a waste of time. I use it in conjuction with file creation times to check that I didn't forget to update/create one of the data files a process might need. Since I have to create the data file manually, race conditions seem unlikely. -- Neil Cerutti -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
On Mon, Nov 11, 2013 at 5:26 PM, Matt mattgrav...@gmail.com wrote: So I want to take the file, desktop/test.txt and write it to desktop/newfolder/test.txt. I tried the below script, and it gave me: IOError: [Errno 2] No such file or directory: 'desktop/%s.txt'. Any suggestions would be great. Its better in the future to cut and paste the traceback rather than paraphrase... That being said, it can't find the in_file. Maybe you aren't in the directory above desktop? Try specifying a complete path, instead of relative. Once you solve that, be sure the ouput path is specificed completely and that it exists. def firstdev(file): in_file = open(desktop/%s.txt) % file indata = in_file.read() out_file = open(desktop/newfolder/%s.txt, 'w') % file out_file.write(indata) out_file.close() in_file.close() firstdev(test) -- https://mail.python.org/mailman/listinfo/python-list -- Joel Goldstick http://joelgoldstick.com -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
On Tue, Nov 12, 2013 at 9:26 AM, Matt mattgrav...@gmail.com wrote: So I want to take the file, desktop/test.txt and write it to desktop/newfolder/test.txt. I tried the below script, and it gave me: IOError: [Errno 2] No such file or directory: 'desktop/%s.txt'. Any suggestions would be great. def firstdev(file): in_file = open(desktop/%s.txt) % file indata = in_file.read() out_file = open(desktop/newfolder/%s.txt, 'w') % file You're using the % operator, which does your interpolations, at the wrong point. You want to be adjusting the file name, not adjusting the opened file: in_file = open(desktop/%s.txt % file) out_file = open(desktop/newfolder/%s.txt % file, 'w') ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
On 11/11/2013 5:26 PM, Matt wrote: So I want to take the file, desktop/test.txt and write it to desktop/newfolder/test.txt. I tried the below script, and it gave me: IOError: [Errno 2] No such file or directory: 'desktop/%s.txt'. Any suggestions would be great. def firstdev(file): in_file = open(desktop/%s.txt) % file The problem is the above line. Rewrite is thus: in_file = open(desktop/%s.txt % file) indata = in_file.read() out_file = open(desktop/newfolder/%s.txt, 'w') % file Same here: out_file = open(desktop/newfolder/%s.txt% file, 'w') out_file.write(indata) out_file.close() in_file.close() Also don't get in the habit of reassigning built-in functions e;g; file. firstdev(test) -- Bob Gailer 919-636-4239 Chapel Hill NC -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
Sorry for incorect answer. Those guys nailed it On Nov 11, 2013 5:43 PM, bob gailer bgai...@gmail.com wrote: On 11/11/2013 5:26 PM, Matt wrote: So I want to take the file, desktop/test.txt and write it to desktop/newfolder/test.txt. I tried the below script, and it gave me: IOError: [Errno 2] No such file or directory: 'desktop/%s.txt'. Any suggestions would be great. def firstdev(file): in_file = open(desktop/%s.txt) % file The problem is the above line. Rewrite is thus: in_file = open(desktop/%s.txt % file) indata = in_file.read() out_file = open(desktop/newfolder/%s.txt, 'w') % file Same here: out_file = open(desktop/newfolder/%s.txt% file, 'w') out_file.write(indata) out_file.close() in_file.close() Also don't get in the habit of reassigning built-in functions e;g; file. firstdev(test) -- Bob Gailer 919-636-4239 Chapel Hill NC -- https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
On 11/11/2013 22:26, Matt wrote: So I want to take the file, desktop/test.txt and write it to desktop/newfolder/test.txt. I tried the below script, and it gave me: IOError: [Errno 2] No such file or directory: 'desktop/%s.txt'. Any suggestions would be great. def firstdev(file): in_file = open(desktop/%s.txt) % file in_file = open(desktop/%s.txt % file) indata = in_file.read() out_file = open(desktop/newfolder/%s.txt, 'w') % file out_file.write(indata) out_file.close() in_file.close() firstdev(test) -- Python is the second best programming language in the world. But the best has yet to be invented. Christian Tismer Mark Lawrence -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
On Monday, November 11, 2013 4:26:46 PM UTC-6, Matt wrote: So I want to take the file, desktop/test.txt and write it to desktop/newfolder/test.txt. I tried the below script, and it gave me: IOError: [Errno 2] No such file or directory: 'desktop/%s.txt'. Any suggestions would be great. def firstdev(file): in_file = open(desktop/%s.txt) % file indata = in_file.read() out_file = open(desktop/newfolder/%s.txt, 'w') % file out_file.write(indata) out_file.close() in_file.close() firstdev(test) 1. i believe win32 file paths require a qualifying volume letter. 2. Never, ever, *EVER* write data to disc before confirming the paths your passing are pointing to the location you intended to write the data. Use os.path.exists(path) to test your paths BEFORE trying to write data. 3. Be sure your variables names are both self documenting and non clobbering. psst: file is a builtin! Using filename would be a far wiser choice for a variable containing a filename. When i see file, i think of a file object 4. When dealing with files you must be sure that exceptions are handled cleanly. You don't want open file objects floating aimlessly around in memory because your naive code blew chunks. 5. Remember, you cannot write a file into a directory that does not exist. 6 For OS compatibility always use os.path.join() to join path parts into a whole. This method will insert the proper separator for you depending on the OS. -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
Thank you guys so much. Brain fart moment. I appreciate it -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
On Tue, Nov 12, 2013 at 9:51 AM, Rick Johnson rantingrickjohn...@gmail.com wrote: On Monday, November 11, 2013 4:26:46 PM UTC-6, Matt wrote: So I want to take the file, desktop/test.txt and write it to desktop/newfolder/test.txt. I tried the below script, and it gave me: IOError: [Errno 2] No such file or directory: 'desktop/%s.txt'. Any suggestions would be great. def firstdev(file): in_file = open(desktop/%s.txt) % file indata = in_file.read() out_file = open(desktop/newfolder/%s.txt, 'w') % file out_file.write(indata) out_file.close() in_file.close() firstdev(test) 1. i believe win32 file paths require a qualifying volume letter. They do not; omitting the drive letter makes the path relative to the current drive (and since it doesn't start with a directory specifier, the current directory). 2. Never, ever, *EVER* write data to disc before confirming the paths your passing are pointing to the location you intended to write the data. Use os.path.exists(path) to test your paths BEFORE trying to write data. Why? Why, oh why? If there's a problem, it'll be signalled with an exception. Testing that the path exists opens you up to race problems, so you won't see anything now, but some day your code will be in a concurrent situation and you'll get unexpected exceptions. Why not just expect the exception? 3. Be sure your variables names are both self documenting and non clobbering. psst: file is a builtin! Using filename would be a far wiser choice for a variable containing a filename. When i see file, i think of a file object This one's arguable. How often do you use the 'file' builtin? I've worked with files in Python innumerable times, and I don't remember the last time I used 'file'. Yes, avoid shadowing important builtins like 'list' and 'int', but 'id' and 'file' aren't that big a deal. 4. When dealing with files you must be sure that exceptions are handled cleanly. You don't want open file objects floating aimlessly around in memory because your naive code blew chunks. They won't float around forever. The garbage collector will get to them. If you're advocating use of 'with', that's only going to be an issue if the code's called in a loop AND if it throws before the close() calls come through. 5. Remember, you cannot write a file into a directory that does not exist. So? Exception thrown, traceback printed to console, process terminated cleanly. I'm not seeing a problem here. 6 For OS compatibility always use os.path.join() to join path parts into a whole. This method will insert the proper separator for you depending on the OS. Technically true. However, most modern OSes will accept a slash. There'll be a few situations where that's not true, but the OP an happily just use slashes for simplicity. Remember the zen: Practicality beats purity. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
On Mon, 11 Nov 2013 14:51:45 -0800, Rick Johnson wrote: 2. Never, ever, *EVER* write data to disc before confirming the paths your passing are pointing to the location you intended to write the data. Use os.path.exists(path) to test your paths BEFORE trying to write data. This is subject to a race condition, which opens you to a security vulnerability: time of check to time of use bugs. If you follow Rick's advice, and write code like this: if os.path.exists(path): write_to(path) # custom function to open and write to the file else: handle_missing_file() your code is doubly buggy. First, os.path.exists only tells you if the path exists, not whether it is writable. Perhaps it is on read-only media, or you don't have permission to open it, or it's a directory. Secondly, even if the file exists at the moment you call os.path.exists, there is no guarantee that it will still exist a moment later when you try writing to it. Another process may delete or rename the file, or change permissions in the meantime. So you have to write: if os.path.exists(path): try: write_to(path) except (IOError, OSError): handle_missing_or_locked_file() else: handle_missing_or_locked_file() But now your test doesn't actually accomplish anything. Worse, just because the path *doesn't* exist when you check using exists, that doesn't mean it won't exist by the time you call write_to! Using os.path.exists before opening a file is, for the most part, a waste of time. -- Steven -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
On Tue, Nov 12, 2013 at 9:44 AM, Joel Goldstick joel.goldst...@gmail.com wrote: Sorry for incorect answer. Those guys nailed it Your answer wasn't incorrect, because it didn't give any false information. Bob and I saw the problem itself and gave advice, but you gave useful general advice on how to find the problem, which is worth bearing in mind. Matt, read Joel's response for useful tips on how to figure out what might have gone wrong. :) ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
On Monday, November 11, 2013 5:11:52 PM UTC-6, Chris Angelico wrote: On Tue, Nov 12, 2013 at 9:51 AM, Rick Johnson 1. i believe win32 file paths require a qualifying volume letter. They do not; omitting the drive letter makes the path relative to the current drive (and since it doesn't start with a directory specifier, the current directory). Hmm. Let's confirm: import os os.path.exists(C:/Windows/System32) True os.path.exists(/Windows/System32) True Yep, it's official. Implicit File Path Resolution I need to author a PyWart on this soon! 2. Never, ever, *EVER* write data to disc before confirming the paths your passing are pointing to the location you intended to write the data. Use os.path.exists(path) to test your paths BEFORE trying to write data. Why? Why, oh why? If there's a problem, it'll be signalled with an exception. Except when there's a problem that won't be signaled by an EXCEPTION, but will be signaled by EMOTIONS; like for instance removing the wrong directory or truncating the wrong file because of a typo in your source code. OPPS! :-'( Testing that the path exists opens you up to race problems, so you won't see anything now, but some day your code will be in a concurrent situation and you'll get unexpected exceptions. Why not just expect the exception? Because today i'm not facing a concurrent situation, so i'm not going to bother and protect from it. Just like i'm not facing a snake bite, so i won't bother to lug around a vial of antidote. Your attempts to discredit me via hypothetical scenarios is entertaining however. This one's arguable. How often do you use the 'file' builtin? I've worked with files in Python innumerable times, and I don't remember the last time I used 'file'. Yes, avoid shadowing important builtins like 'list' and 'int', but 'id' and 'file' aren't that big a deal. My first concern is with the OP adopting self documenting names. Shadowing file is merely ensuring that the OP knows file is a builtin. Shadowing any builtin can create very difficult bugs to track. This is the point the OP should remember. They won't float around forever. The garbage collector will get to them. That depends on how they are stored. You make too many assumptions Chris. I don't have an problems with GC's, but i'm not about to write sloppy code and assume the GC is going to swoop in and save me like a feline trapped in a tree. 5. Remember, you cannot write a file into a directory that does not exist. So? Exception thrown, traceback printed to console, process terminated cleanly. I'm not seeing a problem here. Now you're just trolling! def firstdev(file): in_file = open(desktop/%s.txt) % file indata = in_file.read() out_file = open(desktop/newfolder/%s.txt, 'w') % file Just from reading that code NO ONE could know for sure if newfolder even existed BEFORE the OP tried to open the out_file. Maybe the OP thinks that missing sub-directories are auto-created by the open function, but there's no way to know for sure, hence my comment. 6 For OS compatibility always use os.path.join() to join path parts into a whole. This method will insert the proper separator for you depending on the OS. Technically true. However, most modern OSes will accept a slash. There'll be a few situations where that's not true, but the OP an happily just use slashes for simplicity. Many a developer have lived to regret those words. PS: I thought Steven was the official devils advocate around here? Hmm. I guess everyone needs a day off. -- https://mail.python.org/mailman/listinfo/python-list
Re: Creating a function for a directory
On Tue, Nov 12, 2013 at 4:42 PM, Rick Johnson rantingrickjohn...@gmail.com wrote: On Monday, November 11, 2013 5:11:52 PM UTC-6, Chris Angelico wrote: On Tue, Nov 12, 2013 at 9:51 AM, Rick Johnson 1. i believe win32 file paths require a qualifying volume letter. They do not; omitting the drive letter makes the path relative to the current drive (and since it doesn't start with a directory specifier, the current directory). Hmm. Let's confirm: import os os.path.exists(C:/Windows/System32) True os.path.exists(/Windows/System32) True Yep, it's official. Implicit File Path Resolution I need to author a PyWart on this soon! That's not a Python issue at all. And are you seriously going to decry relative pathnames?!? 2. Never, ever, *EVER* write data to disc before confirming the paths your passing are pointing to the location you intended to write the data. Use os.path.exists(path) to test your paths BEFORE trying to write data. Why? Why, oh why? If there's a problem, it'll be signalled with an exception. Except when there's a problem that won't be signaled by an EXCEPTION, but will be signaled by EMOTIONS; like for instance removing the wrong directory or truncating the wrong file because of a typo in your source code. Which os.path.exists will not protect you from. So? Testing that the path exists opens you up to race problems, so you won't see anything now, but some day your code will be in a concurrent situation and you'll get unexpected exceptions. Why not just expect the exception? Because today i'm not facing a concurrent situation, so i'm not going to bother and protect from it. Just like i'm not facing a snake bite, so i won't bother to lug around a vial of antidote. Your attempts to discredit me via hypothetical scenarios is entertaining however. 6 For OS compatibility always use os.path.join() to join path parts into a whole. This method will insert the proper separator for you depending on the OS. Technically true. However, most modern OSes will accept a slash. There'll be a few situations where that's not true, but the OP an happily just use slashes for simplicity. Many a developer have lived to regret those words. (Reordered to bring together two comments getting one response) Do you care about what you currently are seeing, or what you might some day see? Concurrency is a common problem on many platforms; platforms not supporting slashes between paths are rare, and most of them will have other porting issues. Why are you ignoring the likely, while trying to prevent the unlikely? They won't float around forever. The garbage collector will get to them. That depends on how they are stored. You make too many assumptions Chris. I don't have an problems with GC's, but i'm not about to write sloppy code and assume the GC is going to swoop in and save me like a feline trapped in a tree. Ah, actually yes you are. When have you ever explicitly disposed of an object in Python? You just let the GC deal with it for you. 5. Remember, you cannot write a file into a directory that does not exist. So? Exception thrown, traceback printed to console, process terminated cleanly. I'm not seeing a problem here. Now you're just trolling! Mercurial signals some errors by dumping an exception to stderr. This works quite nicely, even in production. If your script can't recover from being given a non-writeable directory, don't catch the exception. def firstdev(file): in_file = open(desktop/%s.txt) % file indata = in_file.read() out_file = open(desktop/newfolder/%s.txt, 'w') % file Just from reading that code NO ONE could know for sure if newfolder even existed BEFORE the OP tried to open the out_file. Maybe the OP thinks that missing sub-directories are auto-created by the open function, but there's no way to know for sure, hence my comment. And the OP might have thought that it would automatically publish that to the world, tweet the URL, and create a Facebook status saying just opened a file lolol and get five people to Like it. Doesn't mean we need to probe before doing things. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
