ModuleNotFoundError: no module named ‘fcntl’

In this article, we will explain what the ModuleNotFoundError: no module named ‘fcntl’ means, what causes it, and how to resolve it. This is a confusing error encountered by users and Python developers. This thwarting error can occur due to missing modules from installing Python files. This

Let us look and try to understand the cause of the ModuleNotFoundError: no module named ‘fcntl’ and the ways to rectify it.

What is the ModuleNotFoundError: no module named ‘fcntl’ error about?

When working in the Python programming language, there are many confusing errors that you all have come across; ModuleNotFoundError: no module named ‘fcntl’ is one of them. In Python, fctnl() is a module responsible for open files or input-output controls. It executes file control and handles on the file descriptors and modifies it.

This module performs cmd operations with dependent arguments with different datatypes and values. They mostly provide an interface in low-level input-output functions and file-locking mechanisms in Unix as they are platform-dependent functions.

How ModuleNotFoundError: no module named ‘fcntl’ error is generated?

These are commonly used for concurrency and multiprocessing controls in Python. The error of ModuleNotFoundError: no module named ‘fcntl‘ is generated when a code tries to import this module, but it can’t be located in the system. The occurrence of this error is very low as this module is not available on Windows. Let’s try importing the ‘fctnl’ module.

import fctnl


ModuleNotFoundError: No module named 'fctnl'
ModuleNotFoundError: No module named 'fctnl'

You can see ModuleNotFoundError: No module named ‘fctnl’ warning is raised here. There are several causes for arising this error:

  • It is not available on Windows OS but on standard Linux libraries.
  •  Installation of missing modules due to corrupted Python files.
  • Trying to import the package without installation.
  • Missing ‘fctnl’ module by any container or virtual python environment.

How do you resolve the ModuleNotFoundError: no module named ‘fcntl’ error?

You need to know that the ‘fcntl‘ module is not present on Windows but on the Linux operating system. There is a basic and only way to solve ModuleNotFoundError: no module named ‘fcntl’ error on the Windows operating system.

pip install waitress

The pip install waitress can be upgraded or installed in the pip package organizer. In Python, waitress is a package with adequate performance that can be used on Linux, PyPy 3, and Python 3.8+ versions in Windows. The level of production quality that this package provides is very beneficial when working with the WSGI server on Python.

Currently, 3.0.0, released on February 5, 2024, is the latest version that you can get. With easy configuration and installation, the waitress does not require any subsidiary prerequisites or assembly. The server uses one procedure involving several thread workers.

pip install waitress

After executing the above code, restart the kernel, and the ‘fctnl’ module will work successfully in the Windows operating system. You can install the waitress package organizer on Anaconda Navigator, Google Colab, or Jupyter Notebook. After successfully installing the pip package, restart your kernel and run the ‘fctnl’ module using the code below.

!waitress-serve --listento= prediction :apps

Installing micropython-fcntl

Another solution that can be used is installing the micropython-fcntl. You can use the official Python documentation website to download it and install it by using the following code:

pip install micropython-fcntl


What is Python’s use of the ‘fctnl’ module?

Often used for multiprocessing concordance, the fctnl module provides Unix systems with low-level input-output access and file-locking facilities. It performs file control and handling operations on the file descriptors and updates them. The fctnl module does not work on the Windows operating system.

Is there a Windows equivalent for using the fcntl module?

Several cross-platform options provide low-level input-output access and file-locking facilities on both Windows and Unix systems. The substitute for Windows can be used with the help of win32api. This library uses an interface between the kernal and user applications.

What other errors, besides ModuleNotFoundError, may point to missing modules?

Apart from ModuleNotFoundError, there are several errors in the Python programming language. AttributeError and ImportError are some of those. Attribute error is the error that is raised due to the failure of an assignment or attribute reference. ImportError is the error raised when Python cannot find or import any specific module. Making sure the module name in the warning message is correct is crucial.


To conclude, ModuleNotFoundError: no module named ‘fcntl’ error occurs when the external libraries or the fctnl python module is not available on the current operating system you are working on. But this error is easy to resolve, you cam simply install the waitress package. One thing to note is that ‘fcntl’ will work fine in Linux; this problem only arises when you work with Windows. Watch out for corrupted Python installations, resulting in missing modules responsible for raising this error.


  1. fcntl
  2. waitress
  3. micropython-fcntl

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