How can I execute this python program from mac terminal

Question

I want to execute the following program called APlusB.py in my OSX terminal, enter two numbers for the inputs and have it compute the values and exit. In my terminal I type:

$ python3 APlusB.py

then I get a little cursor on a blank line, I type

3 4

what do I do after that? If I hit Ctl + d then the program terminates, which is what I want, but it prints 7D and I would prefer if it would just compute my value, and print out 7

# Uses python3
import sys
input = sys.stdin.read()
tokens = input.split()
a = int(tokens[0])
b = int(tokens[1])
print(a + b)

Thank you for your help.

yes - I just get more blank lines, the program doesn't exit back to the shell — Greg Bailey
– Greg Bailey, Commented Mar 23, 2016 at 6:05
BTW, you probably get 7D (or, more likely, 7^D) because the program outputs 7 and you typed Ctrl+D. Terminals handle codes of the form Ctrl+Key by signaling the reader program, usually a shell or a program invoked directly or indirectly be the shell, about that. Libraries such as curses can handle stuff so that nothing gets printed and the program can handle the key combo in some way. However, a simple program wont do that, and the terminal will thus echo ^Key by default. For example, most shells, when detecting ^C (a.k.a Ctrl+C), will send SIGINT to the foreground task. — 3442
– 3442, Commented Mar 23, 2016 at 6:11
thank you KemyLand, that makes sense, I wasn't sure how to make the program show me my result and exit properly. — Greg Bailey
– Greg Bailey, Commented Mar 23, 2016 at 6:15
@GregBailey: BTW, the output of the program does not contain D. That's just your terminal mixing up the program's output and other things. If you take your program's output and use it as input for another program, the "D" won't be there. — 3442
– 3442, Commented Mar 23, 2016 at 6:24

jacob · Accepted Answer · 2016-03-23 06:05:31Z

3

sys.stdin.read waits for the user to enter EOF.

Try using input it will return when the user enters a new line. Don't name your variable input as you'll be redefining the input function you'll need to use.

answered Mar 23, 2016 at 6:05

jacob

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3 Comments

Greg Bailey Over a year ago

this code is a sample from a class, and I have zero python experience. In the video, the instructor does some key command to have it just print the number and exit. Isn't Ctl+D EOF, and then shouldn't it just print 7 and not 7D?

Greg Bailey Over a year ago

that definitely works, but I wonder how to send EOF in such a way that you get 7 and not 7D, thank you for your answer.

3442 Over a year ago

@GregBailey: There's no way in "interactive" mode, so to call it (though it's not). See my comment in the question for details. However, you can use pipes to do that, just like this: echo -e '3\n7' | python3 ./APlusB.py.

BlackMamba · Accepted Answer · 2016-03-23 06:13:15Z

1

Please use sys.stdin.readline()

stdin.read(1) reads one character from stdin. If there was more than one character to be read at that point (e.g. the newline that followed the one character that was read in) then that character or characters will still be in the buffer waiting for the next read() or readline().

import sys
input = sys.stdin.readline()
tokens = input.split()
a = int(tokens[0])
b = int(tokens[1])
print(a + b)

the usage:

esekilvxen263 [7:05] [/home/elqstux] -> python wy.py
3 4
7
esekilvxen263 [7:06] [/home/elqstux] ->

edited Mar 23, 2016 at 6:13

answered Mar 23, 2016 at 6:10

BlackMamba

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1 Comment

3442 Over a year ago

You should probably replace your customized shell prompt with $, for clarity's sake.

Alan · Accepted Answer · 2016-03-23 06:16:08Z

0

import sys
input = sys.stdin.read()
tokens = input.split()
a = int(tokens[0])
b = int(tokens[1])
print tokens
print(a + b)

If you put print tokens front print(a+b).It works as you expect.

answered Mar 23, 2016 at 6:16

Alan

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1 Comment

Greg Bailey Over a year ago

I tried this, (had to change it to print(tokens) and then it prints out the tokens array and the product without the D when pressing ctl+D. Interesting. Why in this case does it print out with out the D?

3442 · Accepted Answer · 2016-03-23 06:22:45Z

0

This is the best way to take in input. It is intended for Python 3.

tokens = input()
tokens = tokens.split()
a = int(tokens[0])
b = int(tokens[1]) 
print(a + b)

edited Mar 23, 2016 at 6:22

3442

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answered Mar 23, 2016 at 6:10

Justice

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5 Comments

Open AI - Opting Out Over a year ago

Which version of python?

Open AI - Opting Out Over a year ago

@KemyLand no, it can't convert 3 4 to an integer.

3442 Over a year ago

@PeterWood: Sorry, didn't looked closely. Actually, this doesn't even work for any version of Python...

Open AI - Opting Out Over a year ago

@Justice with your edit it will now print 34 on Python 3.

3442 Over a year ago

@PeterWood: That explains things a little better... Rolled back and edited so that its clear this is for Py3.

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