How do I read a file as the default user input?

Question

How do I read a whole file in python 3.6.x using the user input() function? Like the algorithms challenge sites do. For example:

I have a file with the following content:
```
line 1
line 2
line 3
end
```

My program would do something like:

x = input()
while x != 'end':
    print("I am at", x)
    x = input()

Then I would have as output:

I am at line 1
I am at line 2
I am at line 3

I guess I need to wrap my python sample progam with another program (possible also python, or OS script) that call the first one passing the file as user input. But how could I do it?

Shadow · Accepted Answer · 2017-11-19 22:51:59Z

3

Usually such challenges will pipe the input via stdin, and expected the response via stdout.

To do that, run your command from a command line like so;

python program.py < input.txt

If you want to save the output of the script into a file, you can redirect it to one.

python program.py < input.txt > output.txt

answered Nov 19, 2017 at 22:51

Shadow

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3 Comments

Adailson De Castro Over a year ago

Thanks, @Shadow! I wish I could put you and @wim answers as correct. But I can't do it and he was faster. HAHAHA... My best!

Shadow Over a year ago

Technically I was 3 minutes faster (mouse over the 'answered 1 hour ago' to see the timestamp :P But I don't mind either way.

Adailson De Castro Over a year ago

Ops! You're right. To keep things fair I have set your answer as correct. Sorry for the mess, guys.

wim · Accepted Answer · 2017-11-19 22:59:44Z

2

The usual standard lib tool for this job is the fileinput module:

import fileinput

for line in fileinput.input():
    print(f'working with line {line}')

Then from the shell, take your pick of the following (they all work):

$ python3 my_script.py my_file.txt
$ python3 my_script.py < my_file.txt
$ cat my_file.txt | python3 my_script.py

edited Nov 19, 2017 at 22:59

answered Nov 19, 2017 at 22:54

wim

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