Python File fileno() Method
The descriptor of the file is a low-level identifier that is utilized by the operating system to access a file or a device. To get/retrieve the file descriptor in integer format, the built-in “fileno()” method is utilized in Python. This write-up will provide you with a thorough guide on the “fileno()” method with appropriate examples via the below contents:
- What is the Python File “fileno()” Method?
- Retrieve the Int/Integer File Descriptor
- Creating and Printing the File Descriptor
- Retrieve the Integer File Descriptor After Closing the File
What is the Python File “fileno()” Method?
The integer file descriptor of a stream, which is a numeric value that links an open file with the operating system, can be obtained by using the “fileno()” method in Python. An open file is associated with a numeric value, called a file descriptor, that the operating system uses to refer to the file.
Note: When the file descriptor is not used by the operator system, then the program raises an error.
Syntax
Parameters
No parameters
Return Value
The “fileObject.fileno()” method retrieves the integer file descriptor.
Example 1: Retrieve the Integer File Descriptor
In this example, first, we open the file in read mode and then we retrieve the integer file descriptor by using the “file.fileno()” method.
print(file.fileno())
The below output shows the file descriptor of the input file:
Example 2: Creating and Printing the File Descriptor
We can also create a new file and print their descriptor using the “file.fileno()” method. In the code below, the “open()” function is used multiple times to open/launch the file in write/writing mode. Next, the “file.fileno()” method is used to print the file descriptor. Finally, the file is closed/terminated utilizing the “file.fileno()” method:
file2 = open("new2.txt", "w")
print("file1.fileno(): ", file1.fileno())
print("file2.fileno(): ", file2.fileno())
file1.close()
file2.close()
The below output shows the file descriptor of the multiple input-created files:
Example 3: Retrieve the Integer File Descriptor After Closing the File
We can not retrieve the integer file descriptor after closing the file. Take the following code to demonstrate this example:
print(file1.fileno())
file1.close()
print(file1.fileno())
The following output shows the ValueError:
Conclusion
The “fileno()” method determines the integer of the stream file descriptor. If the operating system does not have a file descriptor for the file, the function will retrieve an error code. We can also create and print the file descriptor of the file using the “fileno()” method. However, once we close the file in Python, the file descriptor becomes inaccessible. This tutorial delivered a comprehensive guide on Python’s “file.fileno()” method using numerous examples.
Source: linuxhint.com