# What's new in PyPy2.7 5.4

Improve CPython compatibility for `is`. Now code like `if x is ():` works the same way as it does on CPython. See https://pypy.readthedocs.io/en/latest/cpython_differences.html#object-identity-of-primitive-values-is-and-id .

Add sys.{get,set}dlopenflags, for cpyext extensions.

Resolves an issue with the generator script to build the dfa for Python syntax.

Fixes a critical issue in the register allocator and extends support on s390x. PyPy runs and translates on the s390x revisions z10 (released February 2008, experimental) and z196 (released August 2010) in addition to zEC12 and z13. To target e.g. z196 on a zEC12 machine supply CFLAGS="-march=z196" to your shell environment.

Implement the backend related changes for s390x.

Simplify handling of interp-level tests and make it more forward- compatible.

Sync w_file with the c-level FILE* before returning FILE* in PyFile_AsFile

Allow rw access to the char* returned from PyString_AS_STRING, also refactor PyStringObject to look like cpython's and allow subclassing PyString_Type and PyUnicode_Type

Bug fix: if `socket.socket()` failed, the `socket.error` did not show the errno of the failing system call, but instead some random previous errno.

Refactor PyTupleObject to look like cpython's and allow subclassing PyTuple_Type

Use offsets from PyTypeObject to find actual c function to call rather than fixed functions, allows function override after PyType_Ready is called

Avoid exhausting the stack in the JIT due to successive guard failures in the same Python function ending up as successive levels of RPython functions, while at app-level the traceback is very short

Try harder to memory to the OS. See e.g. issue #2336. Note that it does not show up as a reduction of the VIRT column in `top`, and the RES column might also not show the reduction, particularly on Linux >= 4.5 or on OS/X: it uses MADV_FREE, which only marks the pages as returnable to the OS if the memory is low.

Fill in more slots when creating a PyTypeObject from a W_TypeObject More slots are still TBD, like tp_print and richcmp

Align json module decode with the cpython's impl, fixes issue 2345

Copy CPython's logic more closely for handling of `__instancecheck__()` and `__subclasscheck__()`. Fixes issue 2343.

Rewrite the Win32 dependencies of 'subprocess' to use cffi instead of ctypes. This avoids importing ctypes in many small programs and scripts, which in turn avoids enabling threads (because ctypes creates callbacks at import time, and callbacks need threads).

The new logging facility that integrates with and adds features to vmprof.com.

Resolve issues to use the new logging facility on a 32bit system

Trying harder to make hash(-1) return -2, like it does on CPython

Log exact line positions in debug merge points.

Allocate all RPython strings with one extra byte, normally unused. It is used to hold a final zero in case we need some `char *` representation of the string, together with checks like `not can_move()` or object pinning. Main new thing that this allows: `ffi.from_buffer(string)` in CFFI. Additionally, and most importantly, CFFI calls that take directly a string as argument don't copy the string any more---this is like CFFI on CPython.

Add a new command line option -X track-resources which will produce ResourceWarnings when the GC closes unclosed files and sockets.

Implement PyObject_Realloc

Improve a little bit the readability of the generated C code

Improved vmprof support: now tries hard to not miss any Python-level frame in the captured stacks, even if there is the metainterp or blackhole interp involved. Also fix the stacklet (greenlet) support.

`type.__dict__` now returns a `dict_proxy` object, like on CPython. Previously it returned what looked like a regular dict object (but it was already read-only).

Reduce the size of the generated C code by constant-folding `we_are_jitted` in non-jitcode.

Support for memoryview attributes (format, itemsize, ...). Extends the cpyext emulation layer.

Log more information to properly rebuild the redirected traces in jitviewer.

Copy Py_TPFLAGS_CHECKTYPES, Py_TPFLAGS_HAVE_INPLACEOPS when inheriting