This changelog summarizes major changes between GraalVM versions of the Python language runtime. The main focus is on user-observable behavior of the engine.

• Escaping Unicode characters using the character names in strings like "\N{GREEK CAPITAL LETTER DELTA}".
• When a *.py file is imported, *.pyc file is created. It contains binary data to speed up parsing.
• Adding option PyCachePrefix, which is equivalent to PYTHONPYCACHEPREFIX environment variable, which is also accepted now.
• Adding optin DontWriteBytecodeFlag. Equivalent to the Python -B flag. Don't write bytecode files.
• Command option -B works
• Implement better reference counting for native extensions to fix memory leaks
• Fix a warning in pandas about size of datetime objects
• Make many more CPython unittests pass for core types
• Support parse requests with arguments for embedding Python to light up GraalVM Insight support
• Support basic tox usage when forcing virtualenv to use venv
• No longer support iterables as arrays in interop
• Add initial support for HPy native extensions
• Support magic encoding comments in Python files
• Improve chaining of exception tracebacks - the tracebacks should now be much closer to CPython and more helpful

• Update language support target and standard library to 3.8.2
• Improve performance of tuples with primitive elements
• Improve performance of using Python sequences from other GraalVM languages
• Improve performance of dictionaries and sets
• Improve performance of allocations for list comprehensions with range iterators
• Support cProfile and trace modules through the GraalVM CPU sampler and coverage, respectively
• Support NumPy on macOS
• Support setuptools-scm and pytz.timezone
• Support new syntax for iterable unpacking from yield and return statements
• Fix issues with inspection and printing of non-Python numbers in the Chrome debugger
• Fix issues with AST sharing across different contexts, if these context run concurrently on multiple threads
• Fix code serialization and deserialization with pickle
• Fix DirEntry.stat
• Fix passing non-ASCII strings to gethostbyname
• Fix help(numpy) to work again in the interactive REPL
• Fix multi-line continuation in the REPL for opening parens
• Fix select.select for pipes
• Polyglot: Rethrow AttributeError as UnknownIdentifierException in invokeMember
• Jython mode: treat Java null as identical to Python None when comparing with the is operator
• Jython mode: isinstance now works with Java classes and objects
• Improve errno handling in posix module
• Move all GraalPython specific functions on sys or builtins to the __graalpython__ module

• Jython Compatiblity: Implement from JavaType import * to import all static members of a Java class
• Jython Compatiblity: Implement importing Python code from inside JAR files by adding path/to/jarfile.jar!path/inside/jar to sys.path
• Added support for date and time interop.
• Added support for setting the time zone via Context.Builder.timeZone.
• PEP 570 - Python Positional-Only Parameters implemented

• Implement gc.{enable,disable,isenabled} as stubs
• Implement charmap_build function
• Implement hexversion in sys module
• Implement _lzma module
• Implement enough of socket.socket to run graalpython -m http.server and download non-encrypted http resources
• Fix printing of Pandas data frames
• Fix a bug in bytes.startswith for tuple arguments
• Fix destructuring assignments of arbitrary iterators
• Fix dict.__contains__ for dictionaries with only str keys for subclasses of str
• Support NumPy 1.16.4 and Pandas 0.25.0
• Support timeit module
• Support basic usage of pytest
• Improve performance across many Python and C extension benchmarks
• Improve performance of our parser
• Improve performance of catching exceptions when the exception does not leave the handler block and the traceback is not accessed
• Improve performance of Java interop when Python objects are accessed from Java
• Add a new --python.EmulateJython flag to support importing Java classes using normal Python import syntax and to catch Java exceptions from Python code
• Update standard library to Python 3.7.4
• Initial implementatin of PEP 498 -- Literal String Interpolation

• Implement PyStructSequence_* C API functions
• Implement _functools.partial as a class instead of a function
• Implement type.__base__
• Implement reading C API type attributes nb_inplace_add, nb_remainder, nb_subtract, and nb_floor_divide for builtin types
• Implement C API functions _PyObject_CallFunction_SizeT, PyEval_InitThreads, and PyEval_ThreadsInitialized
• Implement writing to a function's __dict__ field
• Implement the C API thread state fields overflowed and recursion_depth
• Fix printing of errors in the REPL
• Fix printing full paths in traceback
• Support the C API varargs functions with arbitrary numbers of arguments instead of imposing an upper limit
• Improve performance of attribute reads and reading closure variables

• Add java.add_to_classpath API to dynamically extend the host class path
• Allow write access to main module bindings for embedder
• Swap arguments for polyglot.export_value to use the more natural (name, value) order and deprecate the previous argument order.
• Update Python standard library files to Python 3.7.3
• Improve performance of exceptions that do not escape
• Fix str(None) to print "None" instead of an empty string
• Fix error messages on polyglot objects to not leak implementation class names of those objects
• Fix erroneously frozen package paths in pre-initialized python modules
• Fix caching of core sources in a native image with a preinitialized context for pre-built images and libpolyglot fast startup
• Implement pwd.getpwuid
• Implement os.exec, os.execv, and os.execl
• Add some missing C API headers needed for tensorflow compilation

• Fix an issue preventing use of encodings in the installable binary
• Fix return value of process when os.exit is called with a boolean
• Fix interpretation of foreign objects to prefer interpreting them as integer over double
• Fix performance regression when repeatedly creating a new function in a loop

• No user-facing changes

• Implement PEP 487 __init_subclass__
• Implement PEP 560 __class_getitem__ and __mro_entries__
• Migrate to Truffle libraries for interop
• Support the buffer protocol for mmap
• Support importing java classes using normal Python import syntax
• Improve performance of literal dictionary creation when the first but not all keys are strings
• Improve performance of getting the length of a string
• Improve performance of accessing defaults, keyword-defaults, and code of a function
• Fix getting file separator from the Truffle filesystem rather than the operating system
• Fix constructing and calling methods with non-function callables
• Fix execution of subprocesses with non-default python homes on JVM

• Mark a subset of the Graal Python launcher options as "stable". All other options are subject to change and need to be unlocked explicitly on the commandline.
• Automatically install pip when creating a venv. The socket and ssl libraries are still not functional, so pip can only install from local sources or wheels.
• Update the standard library to Python 3.7.0 from 3.6.5.
• Support the -I flag to ignore the user environment and not add the working directory to sys.path
• Fix an error preventing usage of the memtracer tool. If an object raised an exception in it's __repr__ method, it would abort the execution.
• Fix issues around not being able to modify function defaults, keyword defaults, or re-defining a function with a different closure.
• Fix continuation prompt in the interactive Python shell when an incomplete statement was typed. Before it raised and ignored a SyntaxError.
• Fix frame restarting of Python functions in the Chrome debugger. Before, functions with closures would have their cells accidentally cleared.

• Support marshal.dumps and marshal.loads for code objects and some other built-in objects
• Fix installation of NumPy in a venv
• Initial support for module mmap
• Support debugging with workspace files in the Chrome debugger
• Support the PEP 553 breakpoint() message
• Support running weak reference callbacks and signals on the main thread

• Support the __class__ variable in the class scope
• Support module-level docstrings
• Initial support for the venv standard-library tool
• Initial support for the built-in _bz2 module
• Initial support for the pandas package
• Initial support for OSError subclasses based on the errno of the exception
• Fix bytearray inplace add to return the same object
• Fix access to standard Python methods (__repr__, __str__, __len__ and the like) for foreign objects

• Support running setuptools to build and install various packages
• Support running a source release version of NumPy out of the box
• Improve performance of member access to C API objects
• Improve performance of binary operations on C API objects
• Add support for yield from
• Support assignment to object.__dict__ and ensure that managed subclasses of native types also have a __dict__
• Fix [] access with non-integer keys for array-like foreign objects
• Fix various performance regressions introduced in the last RC
• Implement more built-in methods on the time module
• Python no longer exposes internal languages through polyglot.eval
• Improve performance of os.scandir and functions that build on it (such as glob)
• More correct implementation of standard streams, including buffering
• Properly support the -m switch to run modules
• Support the standard zipfile module
• Add the built-in _cvs module
• Add support for __slots__
• Allow arbitrary callable objects in methods, not only functions
• Report that we have a TTY console if we are launched on a Terminal through our launcher
• Add the ginstall custom module to install known packages such as NumPy and setuptools

• Improve performance of C API upcalls
• Improve performance of classmethods, staticmethods, globals(), and locals()
• Improve performance of various string and bytes operations
• Initial support for the _thread builtin module (actual multi-threading is still disabled, the API defaults to a dummy implementation)
• Implement the zipimporter module
• Support assignment to object.__class__
• Use the new Truffle filesystem API to get/set the current working directory
• Attempt our best to report side-effects in KEY_INFO
• The KEYS message now responds with attributes and methods, never dict keys
• Support the input builtin
• Add DEBUG launcher options for performance debugging
• Ensure context isolation for file descriptors and child PIDs
• Fix passing custom locals and globals through exec and eval
• Fixes to builtin help

• Support help in the builtin Python shell
• Add readline to enable history and autocompletion in the Python shell
• Add support for the -q, -E, -s, and -S Python launcher flags
• Improve display of foreign array-like objects
• Improve support for string and bytes regular expressions using our TRegex engine
• Support loading site-packages installed with easy_install
• Initial support for the binascii module

• Report allocations when the --memtracer option is used
• Initial support for pickle module

• Enhance the java interop builtin module with introspection utility methods

• Support regular expression patterns built from bytes by using CPython's sre module as a fallback engine to our own
• Support LLVM 5+ for C extension modules
• Introduce native sequence storage so that e.g. Python bytes exposed to C can be mutated
• Introduce lazy string concatenation to significantly speed up benchmarks where strings are concatenated repeatedly
• C-API improvements to support more scikit-learn code
• Fix our distinction between builtin functions, functions, and methods to make the classes for builtin functions equivalent to CPython
• Improve set, frozenset, and dict support
• Attach Python exceptions as cause to ImportErrors raised for C extension modules
• Update standard library to CPython 3.6.5
• Support more code object attributes
• Support constant type ids for objects that are interned on CPython
• Add collections.deque
• Document how to contribute
• Improve efficiency of generators
• Enable re-use of ASTs in multiple Contexts in the same Engine

• Generator expressions now properly evaluate their first iterator in the definition scope at definition time
• Fixes for embedders to ensure top scopes are stable and local scopes always contain TruffleObjects
• C-API improvements to support simple Cython modules
• Support recognition of Python source files with the polyglot launcher

• No changes

• Support for more String encodings
• Implement buffered I/O
• Remove our random module substitute and use the standard library implementation
• Fix a potential thread-safety problem with cached parse trees when multiple Python contexts are used from multiple threads
• Complete support for math module builtins
• C-API improvements to run simple scikit-learn and NumPy examples
• Support the buffer protocol to wrap arbitrary Python sequences with no copy into NumPy arrays

• Updates to the polyglot and embedding APIs
• Many additions to the language core implementation
• Performance improvements to the parser
• C-API improvements to compile and run simple C extensions
• Support breakpoints on caught and uncaught exceptions in debugger

• LICENSE set to The Universal Permissive License (UPL), Version 1.0.