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In Python, you can redirect input to come from a file rather than just typed input by the user. This allows you to feed data into your program from a file on disk rather than manual input.
Redirecting file input to stdin is useful for:
Automating input into Python scripts
Running batch operations
Loading structured data from files
Isolating input dependencies for testing
Python makes redirecting file input to stdin easy once you understand the relevant classes and functions involved:
Python’s Standard Input Stream
The standard input stream in Python, stdin, is what receives input data by default, like from input() or console input. This allows a user to dynamically provide input to your script.
Under the hood, stdin is a file-like object that reads from the keyboard input buffer. But you can swap out where it reads from to any file by redirecting stdin.
The sys Module
Python’s sys module contains attributes for accessing standard streams like stdin, stdout and stderr.
To redirect stdin input to a file, you need to import sys and access the stdin attribute:
importsysinput_stream = sys.stdin
Now input_stream represents the stdin file object you can redirect.
Opening the File to Redirect
To redirect a file’s contents to stdin, first open the file using Python’s built-in open() function:
file = open('data.txt')
This opens data.txt for reading input.
Redirecting the File to sys.stdin
Pass the opened file object to sys.stdin using:
sys.stdin = file
Now any input read from stdin will come from data.txt instead of manual input!
Reading from the Redirected Stdin
With the redirection set up, you can read lines using .readline() as if from a user:
This will print the first line of data.txt.
For automated batch processing, you can iterate over all lines:
This lets you transparently process file input as if it were manual input to your Python program.
Resetting Standard Input
To revert stdin to keyboard input, you can close the file and reset sys.stdin:
file.close()sys.stdin = sys.__stdin__
Now stdin is restored for interactive user input.
Full Example Code
Here is complete code to demonstrate file input redirection in Python:
importsysprint('Stdin before:', sys.stdin)file = open('data.txt')print('Redirecting file to stdin') sys.stdin = fileprint('Stdin after:', sys.stdin) print(sys.stdin.readline())forlineinsys.stdin:print(line)print('Closing file and resetting stdin')file.close() sys.stdin = sys.__stdin__print('Stdin after reset:', sys.stdin)print('Type some manual input:')manual_input = input() # Nowfromkeyboardagain
This shows the full process of redirecting a file to stdin, reading the redirected input, then resetting it back to normal.
The key points to remember about redirecting input from a file to stdin in Python are:
Import sys to access stdin for redirection
Open the file with open() in read mode
Redirect using sys.stdin = file_object
Read redirected input with sys.stdin
Reset stdin using sys.stdin = sys.__stdin__ after
Redirecting file input to stdin is extremely useful for automating Python scripts and decoupling input sources from code. Master input redirection in Python to write flexible, batchable programs ready for real-world data pipelines.
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