How to Read Input From stdin in Python

1. Use fileinput.input() to Read From stdin in Python
2. Use sys.stdin to Read From stdin in Python
3. Conclusion

This tutorial discusses methods to read input from stdin in Python. This can be either reading from the console directly or reading from the filename specified in the console.

Use fileinput.input() to Read From stdin in Python

We can use the fileinput module to read from stdin in Python. fileinput.input() reads through all the lines in the input file names specified in command-line arguments. If no argument is specified, it will read the standard input provided.

The below example illustrates reading from the input file name specified.

We will use the sample.txt below.

Hello
Line1

Line2

Below the script read.py.

import fileinput

for line in fileinput.input():
    print(line.rstrip())

We execute it like this:

python read.py "sample.txt"

Output:

Hello
Line1

Line2

The below example illustrates reading from standard input.

import fileinput

for line in fileinput.input():
    print("Output:", line.rstrip())

The execution and output is shown below.

python read.py
Line 1
Output: Line 1
Line 2
Output: Line2
^Z

We can save the data to be processed later as well like this:

import fileinput

data = []
for line in fileinput.input():
    data.append(line.rstrip())

Note that we are using line.rstrip(). That is to remove the trailing newline.

Typing in y deletes all the variables.

Use sys.stdin to Read From stdin in Python

Another approach is to use sys.stdin to read from stdin in Python. The below example illustrates reading data from stdin line by line:

import sys

for line in sys.stdin:
    print("Output:", line.rstrip())

The execution and output is shown below.

python read.py
Line 1
Output: Line 1
Line 2
Output: Line2
^Z

We can also read all the data from stdin in one go instead of line by line.

The below example illustrates this:

import sys

data = sys.stdin.readlines()
data = [line.rstrip() for line in data]

Note that we are using line.rstrip(). That is to remove the trailing newline.

Conclusion

We discussed 2 methods, fileinput.input() and sys.stdin, to read stdin input in Python. fileinput.input() can read data from the specified file name in the command line argument or from the standard input, while sys.stdin can only read data from the standard input.