prog1.py | prog2.exe

[guest@localhost ~]$ python3 -c 'print(1); input(); print(2)' | cat -n
     1  1
x
     2  2
[guest@localhost ~]$

#one.py
import time
for i in xrange(5):
    print 'I can do it, i will print value {}'.format(i)
    time.sleep(1)

python one.py  | tee 

import time, sys
for i in xrange(5):
    print 'I can do it, i will print value {}'.format(i)
    sys.stdout.flush()
    time.sleep(1)

import time, sys
for i in xrange(500):
    print 'I can do it, i will print value {}'.format(i)
    time.sleep(0.01)

   At program startup, three text streams are predefined and need not
be opened explicitly --- standard input (for reading conventional
input), standard output (for writing conventional output), and
standard error (for writing diagnostic output).  When opened, the
standard error stream is not fully buffered; the standard input and
standard output streams are fully buffered if and only if the stream
can be determined not to refer to an interactive device.

#include <stdio.h>
#include <unistd.h>

int main(void)
{
    int i;

    for (i = 0; i < 3; i++) {
        printf("Test %d\n", i);
        sleep(1);
    }
    return 0;
}

[guest@localhost c]$ .ansi t.c -o t
[guest@localhost c]$ ./t
Test 0
Test 1
Test 2
[guest@localhost c]$ 

[guest@localhost c]$ ./t | cat -n
     1  Test 0
     2  Test 1
     3  Test 2
[guest@localhost c]$

[guest@localhost ~]$ python3 -c 'import time; print(1); time.sleep(2); print(2)'
1
2
[guest@localhost ~]$ python3 -c 'import time; print(1); time.sleep(2); print(2)' | cat -n
     1  1
     2  2
[guest@localhost ~]$