Standard Input and Standard Output in Python

We will provide an example of how you read a file with the standard input and how to write the file with the standard output in Python. We could provide the following descriptions for the standard input and output:

• Standard input – Is the “I/O stream” that reads and input.
• Standard output – It writes the output to the ‘I/O stream”

The next graph provides some examples about redirections:

Let’s provide an example of how we can get an input from a file with the standard input and to write a file with the standard output. The task is the following:

• Write a Python script which takes file as standard input
• It reverses the text of each line
• It saves the standard output to a new file called output.txt

My stdinout.py is the one below:

import sys

stdin = sys.stdin

# Redirect sys.stdout to the file
sys.stdout = open('output.txt', 'w')

for line in stdin:
    if len(line)>0:
        print(line.strip()[::-1])
    
sys.stdout.close()

Assume that the example input called myfile.txt is the following:

1.George
2.Jim
3.Maria
4.Joe
5.Steve
6.Stella

Now we can run our script with the following command:

python stdinout.py < myfile.txt

Note the < which means that we redirected the standard input. Finally, we get the following output called output.txt:

egroeG.1
miJ.2
airaM.3
eoJ.4
evetS.5
alletS.6

As we can we, it reversed each line as expected!

Good job!