Python iterate over stdin line by line using input()

Question

I am trying to get multiple names separated by newlines from the console and put them into a variable. Let's assume I want to get input from the terminal forever (I'll add some code to break out of the loop later). I know how to do it with a while loop and recursion, but I would like to be able to do it with a for loop.

In the below example when I get "peter" as input from the terminal I get each letter rather than a whole line at a time:

for name in input():
    print(name)

Now, if I use sys.stdin the name variable becomes "peter\n":

for name in sys.stdin:
    print(name)

Is there a easy way to get input() to give "name" a whole line rather than individual characters? Or just by the nature of using for in I am going to be iterating through the characters in the input? Are there any inherent risks/problems with getting input in this fashion? Is there a "standard" way of getting input in a situation like this?

I am using Python 3.5.1 on Ubuntu 15.10.

input() returns a string which is an iterable, so therefore when you try and iterate over it you are getting each character one by one. — James Buck
– James Buck, Commented Jan 30, 2016 at 1:18
Ok that makes sense. input() returns a string. So does sys.stdin return a buffer that is iterated line by line? — PeterH
– PeterH, Commented Jan 30, 2016 at 1:20
Because sys.stdin returns a file like object which, when iterated through, will contain each individual line of the input. — James Buck
– James Buck, Commented Jan 30, 2016 at 1:23
@PeterH sys.stdin isn't a function, it actually is a file object which is used by the system to get the standard input, therefore for name in sys.stdin behaves like it would do on a file: reading it line by line. — Marco Bonelli
– Marco Bonelli, Commented Jan 30, 2016 at 1:23
Cool makes sense. If I am using 'for name in sys.stdin' that would exit the loop when the input ends correct? — PeterH
– PeterH, Commented Jan 30, 2016 at 1:26

ShadowRanger · Accepted Answer · 2016-10-06 15:26:17Z

You can wrap stdin to strip the newlines; if you can strip all trailing whitespace (usually okay), then it's just:

for name in map(str.rstrip, sys.stdin):
    ...

You're on Py3, so that works as is; if you're on Py2, you'll need to add an import, from future_builtins import map, so you get a lazy, generator based map (that yields the lines as they're requested, rather than slurping stdin until it ends, then returning a list of all the lines).

If you need to limit to newlines, a generator expression can do it:

for name in (line.rstrip("\r\n") for line in sys.stdin):
    ...

or with an import to allow map to push work to C layer for (slightly) faster code (a matter of 30-some nanoseconds per line faster than the genexpr, but still 40 ns per line slower than the argumentless option at the top of this answer):

from operator import methodcaller

for name in map(methodcaller('rstrip', '\r\n'), sys.stdin):
    ...

Like the first solution, on Py2, make sure to get the map from future_builtins.

Marco Bonelli · Accepted Answer · 2016-01-30 01:28:08Z

3

I wouldn't recommend you this, but you can create a generator to be used in a for loop to iterate through input line by line:

def getlines():
    while True:
        yield input()

for name in getlines():
    print(name)
    ## Remember to break out of the loop at some point

edited Jan 30, 2016 at 1:28

answered Jan 30, 2016 at 1:17

Marco Bonelli

71.1k21 gold badges129 silver badges153 bronze badges

2 Comments

PeterH Over a year ago

Sorry if I was unclear. I am trying to do it more than one time with each name separated by a newline in the terminal.

Murilo Perrone Over a year ago

This seems perfect for the simplest line-by-line reading. And the iterator could be enhanced to split that line into smaller parts, yielding those parts one by one.

Collectives™ on Stack Overflow

Python iterate over stdin line by line using input()

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related