[Python-checkins] cpython: Closes #13761: add a "flush" keyword argument to print().

Fri Jan 13 19:42:17 CET 2012

http://hg.python.org/cpython/rev/3120a988a1a3
changeset: 74359:3120a988a1a3
user: Georg Brandl <georg at python.org>
date: Fri Jan 13 19:41:25 2012 +0100
summary:
 Closes #13761: add a "flush" keyword argument to print().
files:
 Doc/library/functions.rst | 11 +++++++----
 Lib/test/test_print.py | 26 ++++++++++++++++++++++++++
 Misc/NEWS | 3 +++
 Python/bltinmodule.c | 24 +++++++++++++++++++-----
 4 files changed, 55 insertions(+), 9 deletions(-)

diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -946,7 +946,7 @@
 must be of integer types, and *y* must be non-negative.
 
 
-.. function:: print([object, ...], *, sep=' ', end='\\n', file=sys.stdout)
+.. function:: print([object, ...], *, sep=' ', end='\\n', file=sys.stdout, flush=False)
 
 Print *object*\(s) to the stream *file*, separated by *sep* and followed by
 *end*. *sep*, *end* and *file*, if present, must be given as keyword
@@ -959,9 +959,12 @@
 *end*.
 
 The *file* argument must be an object with a ``write(string)`` method; if it
- is not present or ``None``, :data:`sys.stdout` will be used. Output buffering
- is determined by *file*. Use ``file.flush()`` to ensure, for instance,
- immediate appearance on a screen.
+ is not present or ``None``, :data:`sys.stdout` will be used. Whether output
+ is buffered is usually determined by *file*, but if the *flush* keyword
+ argument is true, the stream is forcibly flushed.
+
+ .. versionchanged:: 3.3
+ Added the *flush* keyword argument.
 
 
 .. function:: property(fget=None, fset=None, fdel=None, doc=None)
diff --git a/Lib/test/test_print.py b/Lib/test/test_print.py
--- a/Lib/test/test_print.py
+++ b/Lib/test/test_print.py
@@ -111,6 +111,32 @@
 self.assertRaises(TypeError, print, '', end=3)
 self.assertRaises(AttributeError, print, '', file='')
 
+ def test_print_flush(self):
+ # operation of the flush flag
+ class filelike():
+ def __init__(self):
+ self.written = ''
+ self.flushed = 0
+ def write(self, str):
+ self.written += str
+ def flush(self):
+ self.flushed += 1
+
+ f = filelike()
+ print(1, file=f, end='', flush=True)
+ print(2, file=f, end='', flush=True)
+ print(3, file=f, flush=False)
+ self.assertEqual(f.written, '123\n')
+ self.assertEqual(f.flushed, 2)
+
+ # ensure exceptions from flush are passed through
+ class noflush():
+ def write(self, str):
+ pass
+ def flush(self):
+ raise RuntimeError
+ self.assertRaises(RuntimeError, print, 1, file=noflush(), flush=True)
+
 def test_main():
 support.run_unittest(TestPrint)
 
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@
 Core and Builtins
 -----------------
 
+- Issue #13761: Add a "flush" keyword argument to the print() function,
+ used to ensure flushing the output stream.
+
 - Issue #13645: pyc files now contain the size of the corresponding source
 code, to avoid timestamp collisions (especially on filesystems with a low
 timestamp resolution) when checking for freshness of the bytecode.
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -1484,15 +1484,15 @@
 static PyObject *
 builtin_print(PyObject *self, PyObject *args, PyObject *kwds)
 {
- static char *kwlist[] = {"sep", "end", "file", 0};
+ static char *kwlist[] = {"sep", "end", "file", "flush", 0};
 static PyObject *dummy_args;
- PyObject *sep = NULL, *end = NULL, *file = NULL;
+ PyObject *sep = NULL, *end = NULL, *file = NULL, *flush = NULL;
 int i, err;
 
 if (dummy_args == NULL && !(dummy_args = PyTuple_New(0)))
- return NULL;
- if (!PyArg_ParseTupleAndKeywords(dummy_args, kwds, "|OOO:print",
- kwlist, &sep, &end, &file))
+ return NULL;
+ if (!PyArg_ParseTupleAndKeywords(dummy_args, kwds, "|OOOO:print",
+ kwlist, &sep, &end, &file, &flush))
 return NULL;
 if (file == NULL || file == Py_None) {
 file = PySys_GetObject("stdout");
@@ -1543,6 +1543,20 @@
 if (err)
 return NULL;
 
+ if (flush != NULL) {
+ PyObject *tmp;
+ int do_flush = PyObject_IsTrue(flush);
+ if (do_flush == -1)
+ return NULL;
+ else if (do_flush) {
+ tmp = PyObject_CallMethod(file, "flush", "");
+ if (tmp == NULL)
+ return NULL;
+ else
+ Py_DECREF(tmp);
+ }
+ }
+
 Py_RETURN_NONE;
 }
 
-- 
Repository URL: http://hg.python.org/cpython
