SF patch #1397960: When mixing file-iteration and
readline/readlines/read/readinto, loudly break by raising ValueError, rather
than silently deliver data out of order or hitting EOF prematurely.
Probably not a bugfix candidate, even though it affects no 'working' code.
diff --git a/Lib/test/test_file.py b/Lib/test/test_file.py
index bde3202..69501df 100644
--- a/Lib/test/test_file.py
+++ b/Lib/test/test_file.py
@@ -3,7 +3,7 @@
from array import array
from weakref import proxy
-from test.test_support import verify, TESTFN, TestFailed
+from test.test_support import verify, TESTFN, TestFailed, findfile
from UserList import UserList
# verify weak references
@@ -228,3 +228,113 @@
bug801631()
finally:
os.unlink(TESTFN)
+
+# Test the complex interaction when mixing file-iteration and the various
+# read* methods. Ostensibly, the mixture could just be tested to work
+# when it should work according to the Python language, instead of fail
+# when it should fail according to the current CPython implementation.
+# People don't always program Python the way they should, though, and the
+# implemenation might change in subtle ways, so we explicitly test for
+# errors, too; the test will just have to be updated when the
+# implementation changes.
+dataoffset = 16384
+filler = "ham\n"
+assert not dataoffset % len(filler), \
+ "dataoffset must be multiple of len(filler)"
+nchunks = dataoffset // len(filler)
+testlines = [
+ "spam, spam and eggs\n",
+ "eggs, spam, ham and spam\n",
+ "saussages, spam, spam and eggs\n",
+ "spam, ham, spam and eggs\n",
+ "spam, spam, spam, spam, spam, ham, spam\n",
+ "wonderful spaaaaaam.\n"
+]
+methods = [("readline", ()), ("read", ()), ("readlines", ()),
+ ("readinto", (array("c", " "*100),))]
+
+try:
+ # Prepare the testfile
+ bag = open(TESTFN, "w")
+ bag.write(filler * nchunks)
+ bag.writelines(testlines)
+ bag.close()
+ # Test for appropriate errors mixing read* and iteration
+ for methodname, args in methods:
+ f = open(TESTFN)
+ if f.next() != filler:
+ raise TestFailed, "Broken testfile"
+ meth = getattr(f, methodname)
+ try:
+ meth(*args)
+ except ValueError:
+ pass
+ else:
+ raise TestFailed("%s%r after next() didn't raise ValueError" %
+ (methodname, args))
+ f.close()
+
+ # Test to see if harmless (by accident) mixing of read* and iteration
+ # still works. This depends on the size of the internal iteration
+ # buffer (currently 8192,) but we can test it in a flexible manner.
+ # Each line in the bag o' ham is 4 bytes ("h", "a", "m", "\n"), so
+ # 4096 lines of that should get us exactly on the buffer boundary for
+ # any power-of-2 buffersize between 4 and 16384 (inclusive).
+ f = open(TESTFN)
+ for i in range(nchunks):
+ f.next()
+ testline = testlines.pop(0)
+ try:
+ line = f.readline()
+ except ValueError:
+ raise TestFailed("readline() after next() with supposedly empty "
+ "iteration-buffer failed anyway")
+ if line != testline:
+ raise TestFailed("readline() after next() with empty buffer "
+ "failed. Got %r, expected %r" % (line, testline))
+ testline = testlines.pop(0)
+ buf = array("c", "\x00" * len(testline))
+ try:
+ f.readinto(buf)
+ except ValueError:
+ raise TestFailed("readinto() after next() with supposedly empty "
+ "iteration-buffer failed anyway")
+ line = buf.tostring()
+ if line != testline:
+ raise TestFailed("readinto() after next() with empty buffer "
+ "failed. Got %r, expected %r" % (line, testline))
+
+ testline = testlines.pop(0)
+ try:
+ line = f.read(len(testline))
+ except ValueError:
+ raise TestFailed("read() after next() with supposedly empty "
+ "iteration-buffer failed anyway")
+ if line != testline:
+ raise TestFailed("read() after next() with empty buffer "
+ "failed. Got %r, expected %r" % (line, testline))
+ try:
+ lines = f.readlines()
+ except ValueError:
+ raise TestFailed("readlines() after next() with supposedly empty "
+ "iteration-buffer failed anyway")
+ if lines != testlines:
+ raise TestFailed("readlines() after next() with empty buffer "
+ "failed. Got %r, expected %r" % (line, testline))
+ # Reading after iteration hit EOF shouldn't hurt either
+ f = open(TESTFN)
+ for line in f:
+ pass
+ try:
+ f.readline()
+ f.readinto(buf)
+ f.read()
+ f.readlines()
+ except ValueError:
+ raise TestFailed("read* failed after next() consumed file")
+finally:
+ # Bare 'except' so as not to mask errors in the test
+ try:
+ os.unlink(TESTFN)
+ except:
+ pass