Issue 12513: codec.StreamReaderWriter: issues with interlaced read-write (original) (raw)

The following test fails with an AssertionError('a' != 'b') on the first read.

import codecs

FILENAME = 'test'

with open(FILENAME, 'wb') as f: f.write('abcd'.encode('utf-8')) with codecs.open(FILENAME, 'r+', encoding='utf-8') as f: f.write("1")

pos = f.writer.tell()
assert pos == 1, "writer pos: %s != 1" % pos
pos = f.reader.tell()
assert pos == 1, "reader pos: %s != 1" % pos
pos = f.stream.tell()
assert pos == 1, "stream pos: %s != 1" % pos

# read() must call writer.flush()
char = f.read(1)
assert char == 'b', "%r != 'b'" % (char,)
# write() must rewind the raw stream
f.write('3')
tail = f.read()
assert tail == 'd', "%r != 'd'" % (tail,)
f.flush()
with open(FILENAME, 'rb') as f:
    assert f.read() == b'1b3d'

I suppose that readline(), readlines() and next() have also issues.

See also issue #12215: similar issue with io.TextIOWrapper.