* Speed-up "x in y" where x has more than one character.
The existing code made excessive calls to the expensive memcmp() function.
The new code uses memchr() to rapidly find a start point for memcmp().
In addition to knowing that the first character is a match, the new code
also checks that the last character is a match. This significantly reduces
the incidence of false starts (saving memcmp() calls and making quadratic
behavior less likely).
Improves the timings on:
python -m timeit -r7 -s"x='a'*1000" "'ab' in x"
python -m timeit -r7 -s"x='a'*1000" "'bc' in x"
Once this code has proven itself, then string_find_internal() should refer
to it rather than running its own version. Also, something similar may
apply to unicode objects.
(Patch contributed by Nick Coghlan.)
Now joining string subtypes will always return a string.
Formerly, if there were only one item, it was returned unchanged.
hack: it would resize *interned* strings in-place! This occurred because
their reference counts do not have their expected value -- stringobject.c
hacks them. Mea culpa.
interning were not clear here -- a subclass could be mutable, for
example -- and had bugs. Explicitly interning a subclass of string
via intern() will raise a TypeError. Internal operations that attempt
to intern a string subclass will have no effect.
Added a few tests to test_builtin that includes the old buggy code and
verifies that calls like PyObject_SetAttr() don't fail. Perhaps these
tests should have gone in test_string.
bit by checking the value of UCHAR_MAX in Include/Python.h. There was a
check in Objects/stringobject.c. Remove that. (Note that we don't define
UCHAR_MAX if it's not defined as the old test did.)
and left shifts. (Thanks to Kalle Svensson for SF patch 849227.)
This addresses most of the remaining semantic changes promised by
PEP 237, except for repr() of a long, which still shows the trailing
'L'. The PEP appears to promise warnings for operations that
changed semantics compared to Python 2.3, but this is not
implemented; we've suffered through enough warnings related to
hex/oct literals and I think it's best to be silent now.
* Doc - add doc for when functions were added
* UserString
* string object methods
* string module functions
'chars' is used for the last parameter everywhere.
These changes will be backported, since part of the changes
have already been made, but they were inconsistent.
types. The special handling for these can now be removed from save_newobj().
Add some testing for this.
Also add support for setting the 'fast' flag on the Python Pickler class,
which suppresses use of the memo.
Christian Tismer pointed out the high cost of the loop overhead and
function call overhead for 'c' * n where n is large. Accordingly,
the new code only makes lg2(n) loops.
Interestingly, 'c' * 1000 * 1000 ran a bit faster with old code. At some
point, the loop and function call overhead became cheaper than invalidating
the cache with lengthy memcpys. But for more typical sizes of n, the new
code runs much faster and for larger values of n it runs only a bit slower.
Obtain cleaner coding and a system wide
performance boost by using the fast, pre-parsed
PyArg_Unpack function instead of PyArg_ParseTuple
function which is driven by a format string.
When mwh added extended slicing, strings and unicode became mappings.
Thus, dict was set which prevented an error when doing:
newstr = 'format without a percent' % string_value
This fix raises an exception again when there are no formats
and % with a string value.
'%2147483647d' % -123 segfaults. This was because an integer overflow
in a comparison caused the string resize to be skipped. After fixing
the overflow, this could call _PyString_Resize() with a negative size,
so I (1) test for that and raise MemoryError instead; (2) also added a
test for negative newsize to _PyString_Resize(), raising SystemError
as for all bad arguments.
An identical bug existed in unicodeobject.c, of course.
Will backport to 2.2.2.
Also fixed an error message -- %s argument has non-string str()
doesn't make sense for %r, so the error message now differentiates
between %s and %r.
because PyObject_Repr() and PyObject_Str() ensure that this can never
happen. Added a helpful comment instead.
sees a Unicode argument. Unfortunately this test was also executed
for %r, because %s and %r share almost all of their code. This meant
that, if u is a unicode object while repr(u) is an 8-bit string
containing ASCII characters, '%r' % u is a *unicode* string containing
only ASCII characters!
Fixed by executing the test only for %s.
Also fixed an error message -- %s argument has non-string str()
doesn't make sense for %r, so the error message now differentiates
between %s and %r.
of PyString_DecodeEscape(). This prevents a call to
_PyString_Resize() for the empty string, which would
result in a PyErr_BadInternalCall(), because the
empty string has more than one reference.
This closes SF bug http://www.python.org/sf/603937
possible. This always called PyUnicode_Check() and PyString_Check(),
at least one of which would call PyType_IsSubtype(). Also, this would
call PyString_Size() on known string objects.
interning. I modified Oren's patch significantly, but the basic idea
and most of the implementation is unchanged. Interned strings created
with PyString_InternInPlace() are now mortal, and you must keep a
reference to the resulting string around; use the new function
PyString_InternImmortal() to create immortal interned strings.
comments everywhere that bugged me: /* Foo is inlined */ instead of
/* Inline Foo */. Somehow the "is inlined" phrase always confused me
for half a second (thinking, "No it isn't" until I added the missing
"here"). The new phrase is hopefully unambiguous.
Raymond Hettinger
Michael W. Hudson
Armin Rigo
Jeremy Hylton
Marc-André Lemburg
Tim Peters
Martin v. Löwis
Hye-Shik Chang
Skip Montanaro
Guido van Rossum
Fred Drake
Walter Dörwald
Neal Norwitz
Neil Schemenauer