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import unittest
from io import StringIO
from test import support
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 either 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),
}
# 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):
"""Test correct operation of the print function."""
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)]
with support.captured_stdout() as 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))
# errors
self.assertRaises(TypeError, print, '', sep=3)
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)
if __name__ == "__main__":
unittest.main()
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