dvg-pyqt-filelogger 1.4.0

PyQt/PySide interface to handle logging data to file particularly well suited for multithreaded programs.

DvG_PyQt_FileLogger

Provides a PyQt interface to handle logging data to a file particularly well suited for multithreaded programs.

Supports PyQt5, PyQt6, PySide2 and PySide6.

• Github: https://github.com/Dennis-van-Gils/python-dvg-pyqt-filelogger

• PyPI: https://pypi.org/project/dvg-pyqt-filelogger

Installation:

pip install dvg-pyqt-filelogger

Example usage

The following are snippets of code, not a full program.

from qtpy import QtWidgets as QtWid
from dvg_pyqt_filelogger import FileLogger

# Main/GUI thread
# ---------------

class MainWindow(QtWid.QWidget):
    def __init__(
        self,
        log: FileLogger,
        parent=None,
        **kwargs
    ):
        super().__init__(parent, **kwargs)

        # Create a record button
        self.record_button = QtWid.QPushButton("Click to start recording to file")
        self.record_button.setCheckable(True)
        self.record_button.clicked.connect(lambda state: log.record(state))

class YourDataGeneratingDevice:
    reading_1 = 0.0

device = YourDataGeneratingDevice()

def write_header_to_log():
    log.write("elapsed [s]\treading_1\n")

def write_data_to_log():
    log.write(f"{log.elapsed():.3f}\t{device.reading_1:.4f}\n")

log = FileLogger(
    write_header_function=write_header_to_log,
    write_data_function=write_data_to_log
)

log.signal_recording_started.connect(
    lambda filepath: window.record_button.setText(
        f"Recording to file: {filepath}"
    )
)
log.signal_recording_stopped.connect(
    lambda: window.record_button.setText(
        "Click to start recording to file"
    )
)

window = MainWindow(log)

# Data acquisition and/or logging thread
# --------------------------------------

# New data got acquired
device.reading_1 = 20.3

# Must be called whenever new data has become available
log.update()

API

Class FileLogger

FileLogger(
    write_header_function: Callable | None = None,
    write_data_function: Callable | None = None,
    encoding: str = "utf-8",
)

Note

Inherits from: PySide6.QtCore.QObject

Handles logging data to a file particularly well suited for multithreaded programs where one thread is writing data to the log and the other thread (the main/GUI thread) requests starting and stopping of the log, e.g., by the user pressing a button.

The methods start_recording(), stop_recording() and record(bool) can be directly called from the main/GUI thread.

In the logging thread you repeatedly need to call update(). This method takes cares of the state machine behind FileLogger and will perform the appropiate action, such as creating a file on disk, creating the header or writing new data to the log.

Args:

write_header_function (Callable, optional):

Reference to a function that contains your specific code to write a header to the log file. This will get called during update().

The passed function can contain calls to this object’s member methods write(), elapsed() and np_savetxt().

Default: None

write_data_function (Callable, optional):

Reference to a function that contains your specific code to write new data to the log file. This will get called during update().

The passed function can contain calls to this object’s member methods write(), elapsed() and np_savetxt().

Default: None

NOTE:

This class lacks a mutex and is hence not threadsafe from the get-go. As long as update() is being called from inside another mutex, such as a data-acquisition mutex for instance, it is safe.

NOTE:

By design the code in this class will continue on when exceptions occur. They are reported to the command line.

Signals:

signal_recording_started (str):

Emitted whenever a new recording has started. Useful for, e.g., updating text of a record button.

Returns:

The filepath (str) of the newly created log file.

Type:

PySide6.QtCore.Signal()

signal_recording_stopped (pathlib.Path):

Emitted whenever the recording has stopped. Useful for, e.g., updating text of a record button.

Returns:

The filepath as (pathlib.Path()) of the newly created log file. You could use this to, e.g., automatically navigate to the log in the file explorer or ask the user for a ‘save to’ destination.

Type:

PySide6.QtCore.Signal()

Methods:

• set_write_header_function(write_header_function: Callable)

  Will change the parameter write_header_function as originally passed during instantiation to this new callable.

  Args:

  write_header_function (Callable):

  Reference to a function that contains your specific code to write a header to the log file. This will get called during update().

  The passed function can contain calls to this object’s member methods write(), elapsed() and np_savetxt().

• set_write_data_function(write_data_function: Callable)

  Will change the parameter write_data_function as originally passed during instantiation to this new callable.

  Args:

  write_data_function (Callable):

  Reference to a function that contains your specific code to write new data to the log file. This will get called during update().

  The passed function can contain calls to this object’s member methods write(), elapsed() and np_savetxt().

• record(state: bool = True)

  Start or stop recording as given by argument state. Can be called from any thread.

• start_recording()

  Start recording. Can be called from any thread.

• stop_recording()

  Stop recording. Can be called from any thread.

• update(filepath: str = "", mode: str = "a")

  This method will have to get called repeatedly, presumably in the thread where logging is required, e.g., the data-generation thread. This method takes cares of the state machine behind FileLogger and will perform the appropriate action, such as creating a file on disk, creating the header or writing new data to the log.

  Args:

  filepath (str):

  Location of the log file in case it has to be created or opened for write access.

  Default: "{yyMMdd_HHmmss}.txt" denoting the current date and time.

  mode (str, optional):

  Mode in which the log file is to be opened, see open() for more details. Most common options:

  w: Open for writing, truncating the file first.

  a: Open for writing, appending to the end of the file if it exists.

  Defaults: a

• write(data: AnyStr) -> bool

  Write binary or ASCII data to the currently opened log file.

  By design any exceptions occurring in this method will not terminate the execution, but it will report the error to the command line and continue on instead.

  Returns True if successful, False otherwise.

• np_savetxt(*args, **kwargs) -> bool

  Write 1D or 2D array_like data to the currently opened log file. This method passes all arguments directly to numpy.savetxt(), see https://numpy.org/doc/stable/reference/generated/numpy.savetxt.html. This method outperforms FileLogger.write(), especially when large chunks of 2D data are passed (my test shows 8x faster).

  By design any exceptions occurring in this method will not terminate the execution, but it will report the error to the command line and continue on instead.

  Returns True if successful, False otherwise.

• flush()

  Force-flush the contents in the OS buffer to file as soon as possible. Do not call repeatedly, because it causes overhead.

• close()

  Close the log file.

• get_filepath() -> Path | None

  Return the filepath (pathlib.Path | None) of the log.

• is_recording() -> bool

  Is the log currently set to recording?

• elapsed() -> float

  Return the time in seconds (float) since start of recording.

• pretty_elapsed() -> str

  Return the time as “h:mm:ss” (str) since start of recording.

Changelog

1.4.0 (2024-06-24)

• Using qtpy library instead of my own Qt5/6 mechanism

• Support for Numpy 2.0

• Extended API and docstrings

• Added argument encoding, defaulting to “utf-8”

• Added type hints

• Added method get_filepath()

1.3.0 (2023-02-27)

• Raise ImportError instead of general Exception

1.2.0 (2022-09-13)

• Added support for PyQt5, PyQt6, PySide2 and PySide6

1.1.0 (2021-05-13)

• Added support for numpy.savetxt()

1.0.0 (2020-08-11)

• First release on PyPI