Develop Reference

How do I start a COM server? Code is in Python

I want to run Python code as a COM server. Eventually I want to run an RTD server available here. But first I want to know what exactly you have to do to getting any COM server running. So let's focus on this example.
class HelloWorld:
_reg_clsid_ = "{7CC9F362-486D-11D1-BB48-0000E838A65F}"
_reg_desc_ = "Python Test COM Server"
_reg_progid_ = "Python.TestServer"
_public_methods_ = ['Hello']
_public_attrs_ = ['softspace', 'noCalls']
_readonly_attrs_ = ['noCalls']
def __init__(self):
self.softspace = 1
self.noCalls = 0
def Hello(self, who):
self.noCalls = self.noCalls + 1
# insert "softspace" number of spaces
return "Hello" + " " * self.softspace + who
if __name__=='__main__':
import win32com.server.register
win32com.server.register.UseCommandLine(HelloWorld)
Ok, this works in the way that there were no errors and server is registered, hence it is available in the HKEY_CLASSES_ROOT registry. But what can I do with this? Some say you have to compile a instance and have a .dll or .exe file. WHat else do I have to do?

Well, I ran your example. The registry key for the server is at:
HKEY_CLASSES_ROOT\WOW6432Node\CLSID\{7CC9F362-486D-11D1-BB48-0000E838A65F}
It has two subkeys... one for LocalServer32 and one for InProcServer32
I created a simple VBA macro in Excel:
Sub d()
Set obj = CreateObject("Python.TestServer")
MsgBox obj.Hello("joe")
End Sub
Macro ran just fine. My version of Excel is 64-bit. I ran the macro and then fired up Task Manager while the message box was being displayed. I could see pythonw.exe running in the background.
The only difference between my python script and yours is probably the name and also that I added a line to print to make sure I was executing the function:
if __name__=='__main__':
import win32com.server.register
print("Going to register...")
win32com.server.register.UseCommandLine(HelloWorld)
When I ran the 64-bit csript.exe test, it worked... as expected... when I ran the 32-bit version it failed.
I know why...sort of...
The registry entry for InProcServer32 is pythoncom36.dll
That's no good. It is an incomplete path. I tried modifying the path variable on my shell to add to one of the 3 places where the DLL existed on my system, but it didn't work. Also, tried coding the path in the InProcServer32. That didn't work.. kept saying it couldn't find the file.
I ran procmon, and then I observerved that it couldn't load vcruntime140.dll. Found the directory under python where those files were, and added to my path. It got further along. If I cared enough, I might try more. Eventually using procmon, I could find all the problems. But you can do that.
My simple solution was to rename the key InProcServer32 for the CLSID to be _InProcServer32. How does that work? Well, the system can't find InProcServer32 so it always uses LocalServer32--for 32-bit and 64-bit processes. If you need the speed of in process then you'd need to fix the problem by using procmon and being relentless until you solved all the File Not Found errors and such. But, if you don't need the speed of in process, then just using the LocalServer32 might solve the problem.
Caveats I'm using an Anaconda distro that my employer limits access to and I can only install it from the employee store. YMMV.

winreg parameters to retrieve PATH in Windows 10

To retrieve the contents of the %PATH% variable on a Windows 10 Home edition machine, what values should be used for the key, subkey, and name parameters in the following Python script?
import winreg
def _get_reg_value(key, subkey, name):
"""Return registry value specified by key, subkey, and name.
Environment variables in values of type REG_EXPAND_SZ are expanded
if possible.
"""
key = _winreg.OpenKey(key, subkey)
try:
ret = _winreg.QueryValueEx(key, name)
except WindowsError:
return None
else:
key.Close()
if ret[1] == _winreg.REG_EXPAND_SZ:
return expandvars(ret[0])
else:
return ret[0]
Note that we are not using os.environ here because we need to interact with the permanent path values, not just with the runtime values that are exposed by os.environ.
The code example above is from this link . I am using it to study how to interact with the Windows Registry programmatically using Python.
Failed Attempt:
When I call the above function using the following syntax in a .py file run from Windows CMD, all that is returned is a blank line in Windows CMD, followed by a command prompt. As if nothing has happened.
key = winreg.OpenKey(winreg.HKEY_LOCAL_MACHINE, r'SYSTEM\CurrentControlSet\Control\Session Manager')
_get_reg_value(key, 'Environment', 'Path')

If Python's winreg library simply wraps the corresponding Windows APIs, then you have to open each component of the key. You can't say:
winreg.OpenKey(winreg::HKEY_LOCAL_MACHINE, "FOO\\BAR")
Instead, you first have to open FOO and then open BAR:
foo_key = winreg.OpenKey(winreg::HKEY_LOCAL_MACHINE, "FOO")
bar_key = winreg.OpenKey(foo_key, "BAR")
This is likely the root of your problem.
But there may be more to it. After making such a change, you're supposed to broadcast a WM_SETTINGCHANGE so that other processes (like the shell) know to invalidate their caches and reread the system settings. It's likely the PowerShell commandlet does that automatically.
There can be other issues, too. For example, if you're running a 32-bit Python on a 64-bit OS, you might run into Registry redirection, depending exactly on which part(s) of the hive you're trying to access.
To clarify, what you're calling the "permanent path values" is part of the system environment variables. If you have privileges (e.g., running as Administrator), you are correct that you can modify the path from the system environment block at those keys.
The system merges the user environment variables with the system environment variables. If PATH is defined in both environments, the final PATH is the concatenation of the system values followed by the user values. For other variables with both a system and a user definition (e.g., TMP), the user values are used.
Child processes inherit a copy of their parent process's environment. So, even with a WM_SETTINGCHANGE broadcast, they probably won't update their path to reflect changes you've made to the system environment block.

How to get current directory with subprocess?

How can i get the current directory to which I am in? like the use of
os.getcwd()

First, I presume you're not asking about a particular subprocess that exists simply to tell you the current working directory and do nothing else (Apducer's answer). If that were the case you could simply as os.getcwd() and forget the subprocess. You clearly already know that. So you must be dealing with some other (arbitrary?) subprocess.
Second, I presume you understand, via dr1fter's answer, that you have control over the working directory in which the subprocess starts. I suspect that's not enough for you.
Rather, I suspect you're thinking that the subprocess might, according to its own internal logic, have changed its working directory sometime since its launch, that you can't predict where it has ended up, and you want to be able to send some sort of signal to the subprocess at an arbitrary time, to interrogate it about where it's currently working. In general, this is only possible if the process has been specifically programmed with the logic that receives such a signal (through whatever route) and issues such a response. I think that's what SuperStew meant by the comment, "isn't that going to depend on the subprocess?"
I say "in general" because there are platform-specific approaches. For example, see:
windows batch command to determine working directory of a process
How do I print the current working directory of another user in linux?

by default, subprocesses you spawn inherit your PWD. you can however, specify the cwd argument to the subprocess.Popen c'tor to set a different initial PWD.

Unix (Linux, MacOS):
import subprocess
arguments = ['pwd']
directory = subprocess.check_output(arguments)
Windows:
import subprocess
arguments = ['cd']
directory = subprocess.check_output(arguments)
If you want to run in both types of OS, you'll have to check the machine OS:
import os
import subprocess
if os.name == 'nt': # Windows
arguments = ['cd']
else: # other (unix)
arguments = ['pwd']
directory = subprocess.check_output(arguments)

How to get a file close event in python

Using python 2.7 on windows 7 64 bit machine.
How to get a file close event:
when file is opened in a new process of file opener (like notepad, wordpad which opens file everytime in new process of wordpad)
when file is opened in a tab of file opener (like notepad++, which opens all files in new tab but there exist only a single process of notepad++ running)
So, how to get file close event in above cases? Is it possible to achieve above cases through a common code? I am dealing with different file types

This has proven to be a very easy task for *nix systems, but on Windows, getting a file close event is not a simple task. Read below the summary of common methods grouped by OS'es.
For Linux
On Linux, the filesystem changes can be easily monitored, and in great detail. The best tool for this is the kernel feature called inotify, and there is a Python implementation that uses it, called Pynotify.
Pyinotify
Pyinotify is a Python module for monitoring filesystems changes. Pyinotify relies on a Linux Kernel feature (merged in kernel 2.6.13) called inotify, which is an event-driven notifier. Its notifications are exported from kernel space to user space through three system calls. Pyinotify binds these system calls and provides an implementation on top of them offering a generic and abstract way to manipulate those functionalities.
Here you can find the list of the events that can be monitored with Pynotify.
Example usage:
import pyinotify
class EventHandler(pyinotify.ProcessEvent):
def process_IN_CLOSE_NOWRITE(self, event):
print "File was closed without writing: " + event.pathname
def process_IN_CLOSE_WRITE(self, event):
print "File was closed with writing: " + event.pathname
def watch(filename):
wm = pyinotify.WatchManager()
mask = pyinotify.IN_CLOSE_NOWRITE | pyinotify.IN_CLOSE_WRITE
wm.add_watch(filename, mask)
eh = EventHandler()
notifier = pyinotify.Notifier(wm, eh)
notifier.loop()
if __name__ == '__main__':
watch('/path/to/file')
For Windows
Situation for Windows is quite a bit more complex than for Linux. Most libraries rely on ReadDirectoryChanges API which is restricted and can't detect finer details like file close event. There are however other methods for detecting such events, so read on to find out more.
Watcher
Note: Watcher has been last updated in February 2011, so its probably safe to skip this one.
Watcher is a low-level C extension for receiving file system updates using the ReadDirectoryChangesW API on Windows systems. The package also includes a high-level interface to emulate most of the .NET FileSystemWatcher API.
The closest one can get to detecting file close events with Watcher is to monitor the FILE_NOTIFY_CHANGE_LAST_WRITE and/or FILE_NOTIFY_CHANGE_LAST_ACCESS events.
Example usage:
import watcher
w = watcher.Watcher(dir, callback)
w.flags = watcher.FILE_NOTIFY_CHANGE_LAST_WRITE
w.start()
Watchdog
Python API and shell utilities to monitor file system events. Easy install: $ pip install watchdog. For more info visit the documentation.
Watchdog on Windows relies on the ReadDirectoryChangesW API, which brings its caveats as with Watcher and other libraries relying on the same API.
Pywatch
A python near-clone of the Linux watch command. The pywatch.watcher.Watcher class can be told to watch a set of files, and given a set of commands to run whenever any of those files change. It can only monitor the file changed event, since it relies on polling the stat's st_mtime.
Bonus for Windows with NTFS:
NTFS USN Journal
The NTFS USN (Update Sequence Number) Journal is a feature of NTFS which maintains a record of changes made to the volume. The reason it is listed as a Bonus is because unlike the other entries, it is not a specific library, but rather a feature existing on NTFS system. So if you are using other Windows filesystems (like FAT, ReFS, etc..) this does not apply.
The way it works it that the system records all changes made to the volume in the USN Journal file, with each volume having its own instance. Each record in the Change Journal contains the USN, the name of the file, and information about what the change was.
The main reason this method is interesting for this question is that, unlike most of the other methods, this one provides a way to detect a file close event, defined as USN_REASON_CLOSE. More information with a complete list of events can be found in this MSDN article. For a complete documentation about USN Journaling, visit this MSDN page.
There are multiple ways to access the USN Journal from Python, but the only mature option seems to be the ntfsjournal module.
The "proper" way for Windows:
File system filter driver
As descibed on the MSDN page:
A file system filter driver is an optional driver that adds value to
or modifies the behavior of a file system. A file system filter driver
is a kernel-mode component that runs as part of the Windows executive.
A file system filter driver can filter I/O operations for one or more
file systems or file system volumes. Depending on the nature of the
driver, filter can mean log, observe, modify, or even prevent. Typical
applications for file system filter drivers include antivirus
utilities, encryption programs, and hierarchical storage management
systems.
It is not an easy task to implement a file system filter driver, but for someone who would like to give it a try, there is a good introduction tutorial on CodeProject.
P.S. Check #ixe013's answer for some additional info about this method.
Multiplatform
Qt's QFileSystemWatcher
The QFileSystemWatcher class provides an interface for monitoring files and directories for modifications. This class was introduced in Qt 4.2.
Unfortunately, its functionality is fairly limited, as it can only detect when a file has been modified, renamed or deleted, and when a new file was added to a directory.
Example usage:
import sys
from PyQt4 import QtCore
def directory_changed(path):
print('Directory Changed: %s' % path)
def file_changed(path):
print('File Changed: %s' % path)
app = QtCore.QCoreApplication(sys.argv)
paths = ['/path/to/file']
fs_watcher = QtCore.QFileSystemWatcher(paths)
fs_watcher.directoryChanged.connect(directory_changed)
fs_watcher.fileChanged.connect(file_changed)
app.exec_()

The problem you are facing is not with Python, but with Windows. It can be done, but you will have to write some non-trival C/C++ code for it.
A file open or a file close user mode notification does not exist in userland on Windows. That's why the libraries suggested by others do not have file close notification. In Windows, the API to detect changes in userland is ReadDirectoryChangesW. It will alert you of one of the following notifications :
FILE_ACTION_ADDED if a file was added to the directory.
FILE_ACTION_REMOVED if a file was removed from the directory.
FILE_ACTION_MODIFIED if a file was modified. This can be a change in the time stamp or attributes.
FILE_ACTION_RENAMED_OLD_NAME if a file was renamed and this is the old name.
FILE_ACTION_RENAMED_NEW_NAME if a file was renamed and this is the new name.
No amount of Python can change what Windows provides you with.
To get a file close notification, tools like Process Monitor install a Minifilter that lives in the kernel, near the top of other filters like EFS.
To acheive what you want, you would need to:
Install a Minifilter that has the code to send events back to userland. Use Microsoft's Minispy sample, it is stable and fast.
Convert the code from the user program to make it a Python extension (minispy.pyd) that exposes a generator that produces the events. This is the hard part, I will get back to that.
You will have to filter out events, you won't beleive the amount of IO goes on an idle Windows box!
Your Python program can then import your extension and do its thing.
The whole thing looks something like this :
Of course you can have EFS over NTFS, this is just to show that your minifilter would be above all that.
The hard parts :
Your minifilter will have to be digitally signed by an authority Microsoft trusts. Verising comes to mind but there are others.
Debugging requires a separate (virtual) machine, but you can make your interface easy to mock.
You will need to install the minifilter with an account that has adminstrator rights. Any user will be able to read events.
You will have to deal with multi-users your self. There is only one minifilter for many users.
You will have to convert user program from the MiniSpy sample to a DLL, which you will wrap with a Python extension.
The last two are the hardest.

You can use Pyfanotyfi or butter.
I think you'll find this link very usefull: Linux file system events with C, Python and Ruby
There you will find an example about doing exactly what you want(using pyinotify) this is the code:
import pyinotify
DIR_TO_WATCH="/tmp/notify-dir"
FILE_TO_WATCH="/tmp/notify-dir/notify-file.txt"
wm = pyinotify.WatchManager()
dir_events = pyinotify.IN_DELETE | pyinotify.IN_CREATE
file_events = pyinotify.IN_OPEN | pyinotify.IN_CLOSE_WRITE | pyinotify.IN_CLOSE_NOWRITE
class EventHandler(pyinotify.ProcessEvent):
def process_IN_DELETE(self, event):
print("File %s was deleted" % event.pathname) #python 3 style print function
def process_IN_CREATE(self, event):
print("File %s was created" % event.pathname)
def process_IN_OPEN(self, event):
print("File %s was opened" % event.pathname)
def process_IN_CLOSE_WRITE(self, event):
print("File %s was closed after writing" % event.pathname)
def process_IN_CLOSE_NOWRITE(self, event):
print("File %s was closed after reading" % event.pathname)
event_handler = EventHandler()
notifier = pyinotify.Notifier(wm, event_handler)
wm.add_watch(DIR_TO_WATCH, dir_events)
wm.add_watch(FILE_TO_WATCH, file_events)
notifier.loop()

I have not found a package that captures open and close events on Windows. As others have mentioned, pyinotify, is an excellent option for Linux based operating systems.
Since I wasn't able to watch for the closed event, I settled for the modified event. It's very much an 'after the fact' type of solution (ie. I can't pause until I see a file is closed). But, this has worked surprisingly well.
I've used the watchdog package. The code below is from their sample implementation and watches the current directory if you don't pass a path on the command line, otherwise it watches the path you pass.
Example call: python test.py or python test.py C:\Users\Administrator\Desktop
import sys
import time
import logging
from watchdog.observers import Observer
from watchdog.events import LoggingEventHandler
if __name__ == "__main__":
logging.basicConfig(level=logging.INFO,
format='%(asctime)s - %(message)s',
datefmt='%Y-%m-%d %H:%M:%S')
path = sys.argv[1] if len(sys.argv) > 1 else '.'
event_handler = LoggingEventHandler()
observer = Observer()
observer.schedule(event_handler, path, recursive=True)
observer.start()
try:
while True:
time.sleep(1)
except KeyboardInterrupt:
observer.stop()
observer.join()
This code will show you when files are created, modified, deleted or renamed/moved. You can filter by just modified by watching for the on_modified event.

Persistent WinSCP connection for batch copy in Python

I'm trying to copy thousands files to a remote server. These files are generated in real-time within the script. I'm working on a Windows system and need to copy the files to a Linux server (hence the escaping).
I currently have:
import os
os.system("winscp.exe /console /command \"option batch on\" \"option confirm off\" \"open user:pass#host\" \"put f1.txt /remote/dest/\"")
I'm using Python to generate the files but need a way to persist the remote connection so that I can copy each file, to the server, as it is generated (as opposed to creating a new connection each time). That way, I'll only need to change the field in the put option thus:
"put f2 /remote/dest"
"put f3 /remote/dest"
etc.

I needed to do this and found that code similar to this worked well:
from subprocess import Popen, PIPE
WINSCP = r'c:\<path to>\winscp.com'
class UploadFailed(Exception):
pass
def upload_files(host, user, passwd, files):
cmds = ['option batch abort', 'option confirm off']
cmds.append('open sftp://{user}:{passwd}#{host}/'.format(host=host, user=user, passwd=passwd))
cmds.append('put {} ./'.format(' '.join(files)))
cmds.append('exit\n')
with Popen(WINSCP, stdin=PIPE, stdout=PIPE, stderr=PIPE,
universal_newlines=True) as winscp: #might need shell = True here
stdout, stderr = winscp.communicate('\n'.join(cmds))
if winscp.returncode:
# WinSCP returns 0 for success, so upload failed
raise UploadFailed
This is simplified (and using Python 3), but you get the idea.

Instead of using an external program (winscp) you could also use an python ssh-library like pyssh.

You would have to start persistent WinSCP sub-process in Python and feed the put commands to its standard input continuously.
I do not have Python example for this, but there's an equivalent JScript example:
https://winscp.net/eng/docs/guide_automation_advanced#inout
or C# example:
https://winscp.net/eng/docs/guide_dotnet#input
Though using WinSCP .NET assembly via its COM interface for Python would be a way easier:
https://winscp.net/eng/docs/library