Backport of the print function, using a __future__ import.
This work is substantially Anthony Baxter's, from issue
1633807. I just freshened it, made a few minor tweaks,
and added the test cases. I also created issue 2412,
which is to check for 2to3's behavior with the print
function. I also added myself to ACKS.
diff --git a/Lib/__future__.py b/Lib/__future__.py
index d8e14d1..ea14bf3 100644
--- a/Lib/__future__.py
+++ b/Lib/__future__.py
@@ -53,6 +53,7 @@
"division",
"absolute_import",
"with_statement",
+ "print_function",
]
__all__ = ["all_feature_names"] + all_feature_names
@@ -66,6 +67,7 @@
CO_FUTURE_DIVISION = 0x2000 # division
CO_FUTURE_ABSOLUTE_IMPORT = 0x4000 # perform absolute imports by default
CO_FUTURE_WITH_STATEMENT = 0x8000 # with statement
+CO_FUTURE_PRINT_FUNCTION = 0x10000 # print function
class _Feature:
def __init__(self, optionalRelease, mandatoryRelease, compiler_flag):
@@ -114,3 +116,7 @@
with_statement = _Feature((2, 5, 0, "alpha", 1),
(2, 6, 0, "alpha", 0),
CO_FUTURE_WITH_STATEMENT)
+
+print_function = _Feature((2, 6, 0, "alpha", 2),
+ (3, 0, 0, "alpha", 0),
+ CO_FUTURE_PRINT_FUNCTION)
diff --git a/Lib/test/test_print.py b/Lib/test/test_print.py
new file mode 100644
index 0000000..db09c9c
--- /dev/null
+++ b/Lib/test/test_print.py
@@ -0,0 +1,129 @@
+"""Test correct operation of the print function.
+"""
+
+from __future__ import print_function
+
+import unittest
+from test import test_support
+
+import sys
+try:
+ # 3.x
+ from io import StringIO
+except ImportError:
+ # 2.x
+ from StringIO import StringIO
+
+from contextlib import contextmanager
+
+NotDefined = object()
+
+# A dispatch table all 8 combinations of providing
+# sep, end, and file
+# I use this machinery so that I'm not just passing default
+# values to print, I'm eiher passing or not passing in the
+# arguments
+dispatch = {
+ (False, False, False):
+ lambda args, sep, end, file: print(*args),
+ (False, False, True):
+ lambda args, sep, end, file: print(file=file, *args),
+ (False, True, False):
+ lambda args, sep, end, file: print(end=end, *args),
+ (False, True, True):
+ lambda args, sep, end, file: print(end=end, file=file, *args),
+ (True, False, False):
+ lambda args, sep, end, file: print(sep=sep, *args),
+ (True, False, True):
+ lambda args, sep, end, file: print(sep=sep, file=file, *args),
+ (True, True, False):
+ lambda args, sep, end, file: print(sep=sep, end=end, *args),
+ (True, True, True):
+ lambda args, sep, end, file: print(sep=sep, end=end, file=file, *args),
+ }
+
+@contextmanager
+def stdout_redirected(new_stdout):
+ save_stdout = sys.stdout
+ sys.stdout = new_stdout
+ try:
+ yield None
+ finally:
+ sys.stdout = save_stdout
+
+# Class used to test __str__ and print
+class ClassWith__str__:
+ def __init__(self, x):
+ self.x = x
+ def __str__(self):
+ return self.x
+
+class TestPrint(unittest.TestCase):
+ def check(self, expected, args,
+ sep=NotDefined, end=NotDefined, file=NotDefined):
+ # Capture sys.stdout in a StringIO. Call print with args,
+ # and with sep, end, and file, if they're defined. Result
+ # must match expected.
+
+ # Look up the actual function to call, based on if sep, end, and file
+ # are defined
+ fn = dispatch[(sep is not NotDefined,
+ end is not NotDefined,
+ file is not NotDefined)]
+
+ t = StringIO()
+ with stdout_redirected(t):
+ fn(args, sep, end, file)
+
+ self.assertEqual(t.getvalue(), expected)
+
+ def test_print(self):
+ def x(expected, args, sep=NotDefined, end=NotDefined):
+ # Run the test 2 ways: not using file, and using
+ # file directed to a StringIO
+
+ self.check(expected, args, sep=sep, end=end)
+
+ # When writing to a file, stdout is expected to be empty
+ o = StringIO()
+ self.check('', args, sep=sep, end=end, file=o)
+
+ # And o will contain the expected output
+ self.assertEqual(o.getvalue(), expected)
+
+ x('\n', ())
+ x('a\n', ('a',))
+ x('None\n', (None,))
+ x('1 2\n', (1, 2))
+ x('1 2\n', (1, ' ', 2))
+ x('1*2\n', (1, 2), sep='*')
+ x('1 s', (1, 's'), end='')
+ x('a\nb\n', ('a', 'b'), sep='\n')
+ x('1.01', (1.0, 1), sep='', end='')
+ x('1*a*1.3+', (1, 'a', 1.3), sep='*', end='+')
+ x('a\n\nb\n', ('a\n', 'b'), sep='\n')
+ x('\0+ +\0\n', ('\0', ' ', '\0'), sep='+')
+
+ x('a\n b\n', ('a\n', 'b'))
+ x('a\n b\n', ('a\n', 'b'), sep=None)
+ x('a\n b\n', ('a\n', 'b'), end=None)
+ x('a\n b\n', ('a\n', 'b'), sep=None, end=None)
+
+ x('*\n', (ClassWith__str__('*'),))
+ x('abc 1\n', (ClassWith__str__('abc'), 1))
+
+ # 2.x unicode tests
+ x(u'1 2\n', ('1', u'2'))
+ x(u'u\1234\n', (u'u\1234',))
+ x(u' abc 1\n', (' ', ClassWith__str__(u'abc'), 1))
+
+ # errors
+ self.assertRaises(TypeError, print, '', sep=3)
+ self.assertRaises(TypeError, print, '', end=3)
+ self.assertRaises(AttributeError, print, '', file='')
+
+def test_main():
+ test_support.run_unittest(TestPrint)
+
+if __name__ == "__main__":
+ test_main()