Python3 best way to read unknown multi line input

Question

What is the best way in Python 3 to read in multi-line user input when the amount of input is unknown? The multi-line input will be separated by Enter

when I try using

while True:
    line = input()
    if line:
          print(line)
    else:
          break

I receive an EOFError

Then if I change it to a try-catch block

while True:
    line = input()
    try:
          print(line)
    except EOFError:
          break

I still get the EOFError.

That's logical, since the error does not occur at printing, but at input(). So that should be in the try. — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Oct 5, 2017 at 18:26
Are you piping data in from stdin? I've never seen an EOFError from calling input but I suppose it's possible. — Adam Smith
– Adam Smith, Commented Oct 5, 2017 at 18:27
@AdamSmith: yes, if you use Ctrl+D in most terminals, this is also seen as termining the stdin. — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Oct 5, 2017 at 18:30
The dupe is one of the most concise, smartest answers out there. — cs95
– cs95, Commented Oct 5, 2017 at 18:35
@cᴏʟᴅsᴘᴇᴇᴅ the dupe does not answer the question. As specified in my title I ask specifically for Python 3. The dupe is for Python 2 — Mazzone
– Mazzone, Commented Oct 6, 2017 at 21:58

willeM_ Van Onsem · Accepted Answer · 2017-10-05 18:33:46Z

10

The EOFError occurs when you call input(), not when you test it, nor when you print it. So that means you should put input() in a try clause:

try:
    line = input()
    print(line)
except EOFError:
    break

That being said, if input reads from the standard input channel, you can use it as an iterable:

import sys

for line in sys.stdin:
    print(line, end='')

Since every line now ends with the new line character '\n', we can use end='' in the print function, to prevent print a new line twice (once from the string, once from the print function).

I think the last version is more elegant, since it almost syntactically says that you iterate over the stdin and processes the lines individually.

edited Oct 5, 2017 at 18:33

answered Oct 5, 2017 at 18:29

willeM_ Van Onsem

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2 Comments

Elazar Over a year ago

But the last line might cause problems, won't it? Mimicking input() exactly might be subtle

willeM_ Van Onsem Over a year ago

@Elazar: based on the documentation of input, it reads from the stdin, strips the new line, and returns that. And raises an EOFError in case it has an EOF char. This is afaik the same what the iterator protocol over a stdin does (except that it terminates the loop in case of an EOF, and that it does not strip the new line).

Subham · Accepted Answer · 2021-03-06 00:48:54Z

0

Break the loop if input is blank,

a = []
while True:
   user_input = input()
   if user_input == '':
     break
   else:
       a.append(int(user_input))
       
print(sum(a))

produces,

3

3

[Program finished]

If you know the range,

x, *z= [int(input()) for _ in range(3)]
print(x + sum(z))

produces,

3
4
5
12

[Program finished]

answered Mar 6, 2021 at 0:48

Subham

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