Forcing prompt to be on newline when embedding Python with

Thu Jan 5 10:54:42 EST 2017

On Fri, Jan 6, 2017 at 1:06 AM, H Krishnan <hetchkay at gmail.com> wrote:
> I tried replacing sys.displayhook with a function that does not print
> newline but the newline still got inserted. So, I am not sure where the
> newline is coming from. In any case, I could override sys.displayhook to add
> a newline at the end and that seems to resolve my problem.

In Python 2 the newline is written depending on the value of 
sys.stdout.softspace. sys.displayhook initially calls Py_FlushLine, which 
resets the file's softspace to 0 via PyFile_SoftSpace and writes a newline if 
the previous value was non-zero. Next displayhook writes the repr, sets the 
softspace to 1 and calls Py_FlushLine again.
The result you're seeing could occur if your filelike object doesn't have a 
dict or a property to allow setting the "softspace" attribute, as the following 
toy example demonstrates:
 import sys
 class File(object):
 def __init__(self, file):
 self._file = file
 self._sp_enabled = True
 self.softspace = 0
 def write(self, string):
 return self._file.write(string)
 def __getattribute__(self, name):
 value = object.__getattribute__(self, name)
 if name == 'softspace':
 if not self._sp_enabled:
 raise AttributeError
 self._file.write('[get softspace <- %d]\n' % value)
 return value
 def __setattr__(self, name, value):
 if name == 'softspace':
 if not self._sp_enabled:
 raise AttributeError
 self._file.write('[set softspace -> %d]\n' % value)
 object.__setattr__(self, name, value)
softspace enabled:
 >>> sys.stdout = File(sys.stdout)
 [set softspace -> 0]
 [get softspace <- 0]
 [set softspace -> 0]
 >>> 42
 [get softspace <- 0]
 [set softspace -> 0]
 42[get softspace <- 0]
 [set softspace -> 1]
 [get softspace <- 1]
 [set softspace -> 0]
 [get softspace <- 0]
 [set softspace -> 0]
softspace disabled:
 >>> sys.stdout._sp_enabled = False
 >>> 42
 42>>> 42
 42>>>