# Scripts/stdinreader

- `Download example`

…

## stdinreader.py

    #!/usr/bin/env python3

    from Foundation import (
        NSObject,
        NSFileHandle,
        NSNotificationCenter,
        NSFileHandleReadCompletionNotification,
        NSFileHandleNotificationDataItem,
        NSFileHandleError,
    )
    from PyObjCTools import AppHelper

    class FileObserver(NSObject):
        def initWithFileDescriptor_readCallback_errorCallback_(
            self, fileDescriptor, readCallback, errorCallback
        ):
            self = self.init()
            self.readCallback = readCallback
            self.errorCallback = errorCallback
            self.fileHandle = NSFileHandle.alloc().initWithFileDescriptor_(fileDescriptor)
            self.nc = NSNotificationCenter.defaultCenter()
            self.nc.addObserver_selector_name_object_(
                self,
                "fileHandleReadCompleted:",
                NSFileHandleReadCompletionNotification,
                self.fileHandle,
            )
            self.fileHandle.readInBackgroundAndNotify()
            return self

        def fileHandleReadCompleted_(self, aNotification):
            ui = aNotification.userInfo()
            newData = ui.objectForKey_(NSFileHandleNotificationDataItem)
            if newData is None:
                if self.errorCallback is not None:
                    self.errorCallback(self, ui.objectForKey_(NSFileHandleError))
                self.close()
            else:
                self.fileHandle.readInBackgroundAndNotify()
                if self.readCallback is not None:
                    self.readCallback(self, str(newData))

        def close(self):
            self.nc.removeObserver_(self)
            if self.fileHandle is not None:
                self.fileHandle.closeFile()
                self.fileHandle = None
            # break cycles in case these functions are closed over
            # an instance of us
            self.readCallback = None
            self.errorCallback = None

        def __del__(self):
            # Without this, if a notification fires after we are GC'ed
            # then the app will crash because NSNotificationCenter
            # doesn't retain observers.  In this example, it doesn't
            # matter, but it's worth pointing out.
            self.close()

    def prompt():
        sys.stdout.write("write something: ")
        sys.stdout.flush()

    def gotLine(observer, line):
        if line:
            print("you wrote:", line.rstrip())
            prompt()
        else:
            print("")
            AppHelper.stopEventLoop()

    def gotError(observer, err):
        print("error:", err)
        AppHelper.stopEventLoop()

    if __name__ == "__main__":
        import sys

        observer = FileObserver.alloc().initWithFileDescriptor_readCallback_errorCallback_(
            sys.stdin.fileno(), gotLine, gotError
        )
        prompt()
        AppHelper.runConsoleEventLoop(installInterrupt=True)