Metadata-Version: 2.1
Name: x-python
Version: 1.1.0
Summary: Python cross-version byte-code interpeter
Home-page: http://github.com/rocky/xpython
Author: Rocky Bernstein, Ned Batchelder, Paul Swartz, Allison Kaptur and others
Author-email: rb@dustyfeet.com
License: UNKNOWN
Description: |TravisCI| |CircleCI|
        
        x-python
        --------
        
        This is a CPython bytecode interpreter written Python.
        
        You can use this to:
        
        * Learn about how the internals of CPython works since this models that
        * Use as a sandboxed environment for trying pieces of execution
        * Have one Python program that runs multiple versions of Python bytecode.
          For a number of things you can Python 2.5 or 2.6 bytecode from inside Python 3.7;
          No need to install Python 2.5 or 2.6!
        * Use in a dynamic fuzzer or in coholic execution for analysis
        
        The sandboxed environment in a debugger I find interesting. Since
        there is a separate execution, and traceback stack, inside a debugger
        you can try things out in the middle of a debug session without
        effecting the real execution. On the other hand if a sequence of
        executions works out, it is possible to copy this (under certain
        circumstances) back into CPython's execution stack.
        
        Going the other way, I may at some point hook in `my debugger
        <https://pypi.python.org/pypi/trepan3k>`_ into this interpreter and then
        you'll have a conventional pdb/gdb like debugger also with the ability
        to step bytecode instructions.
        
        Another unexplored avenue implied above is mixing interpretation and
        direct CPython execution. In fact, there are bugs so this happens
        right now, but it will be turned into a feature. Some functions or
        classes you may want to not run under a slow interpreter while others
        you do want to run under the interpreter.
        
        
        Examples:
        +++++++++
        
        What to know instructions get run when you write some simple code?
        Try this:
        
        ::
        
           $ xpython -vc "x, y = 2, 3; x **= y"
           INFO:xpython.pyvm2:Line    1,   0: LOAD_CONST (2, 3)
           INFO:xpython.pyvm2:             2: UNPACK_SEQUENCE 2
           INFO:xpython.pyvm2:             4: STORE_NAME 'x'
           INFO:xpython.pyvm2:             6: STORE_NAME 'y'
           INFO:xpython.pyvm2:             8: LOAD_NAME 'x'
           INFO:xpython.pyvm2:            10: LOAD_NAME 'y'
           INFO:xpython.pyvm2:            12: INPLACE_POWER
           INFO:xpython.pyvm2:            14: STORE_NAME 'x'
           INFO:xpython.pyvm2:            16: LOAD_CONST None
           INFO:xpython.pyvm2:            18: RETURN_VALUE
        
        Option `-c` is the same as Python's flag (program passed in as string)
        and `-v` is also analogus Python's flag. Here, it shows the bytecode
        instructions run.
        
        Want the execution stack stack and block stack in addition? Add another `v`:
        
        ::
        
           $ xpython -vvc "x, y = 2, 3; x **= y"
           DEBUG:xpython.pyvm2:make_frame: code=<code object <module> at 0x7f33d1cf01e0, file "<string x, y = 2, 3; x **= y>", line 1>, callargs={}, f_globals=(<class 'dict'>, 139860540041568), f_locals=(<class 'NoneType'>, 94796399066560)
           DEBUG:xpython.pyvm2:<Frame at 0x7f33d135ef50: '<string x, y = 2, 3; x **= y>' @ 1>
           DEBUG:xpython.pyvm2:  frame.stack: []
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:Line    1,   0: LOAD_CONST (2, 3)
           DEBUG:xpython.pyvm2:  frame.stack: [(2, 3)]
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:             2: UNPACK_SEQUENCE 2
           DEBUG:xpython.pyvm2:  frame.stack: [3, 2]
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:             4: STORE_NAME 'x'
           DEBUG:xpython.pyvm2:  frame.stack: [3]
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:             6: STORE_NAME 'y'
           DEBUG:xpython.pyvm2:  frame.stack: []
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:             8: LOAD_NAME 'x'
           DEBUG:xpython.pyvm2:  frame.stack: [2]
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:            10: LOAD_NAME 'y'
           DEBUG:xpython.pyvm2:  frame.stack: [2, 3]
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:            12: INPLACE_POWER
           DEBUG:xpython.pyvm2:  frame.stack: [8]
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:            14: STORE_NAME 'x'
           DEBUG:xpython.pyvm2:  frame.stack: []
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:            16: LOAD_CONST None
           DEBUG:xpython.pyvm2:  frame.stack: [None]
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:            18: RETURN_VALUE
        
        
        The above showed straight-line code, so you see all of the instructions. But don't confuse this with a disassembler like `pydisasm` from `xdis`.
        The below example, with conditional branching example makes this more clear:
        
        ::
        
           $ xpython -vvc "x = 6 if __name__ != '__main__' else 10"
           DEBUG:xpython.pyvm2:make_frame: code=<code object <module> at 0x7f2dd0d2f150, file "<string x = 6 if __name__ !=>", line 1>, callargs={}, f_globals=(<class 'dict'>, 139834753714688), f_locals=(<class 'NoneType'>, 94349724270016)
           DEBUG:xpython.pyvm2:<Frame at 0x7f2dd039ded0: '<string x = 6 if __name__ !=>' @ 1>
           DEBUG:xpython.pyvm2:  frame.stack: []
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:Line    1,   0: LOAD_NAME '__name__'
           DEBUG:xpython.pyvm2:  frame.stack: ['__main__']
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:             2: LOAD_CONST '__main__'
           DEBUG:xpython.pyvm2:  frame.stack: ['__main__', '__main__']
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:             4: COMPARE_OP 3
           DEBUG:xpython.pyvm2:  frame.stack: [False]
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:             6: POP_JUMP_IF_FALSE 12
           DEBUG:xpython.pyvm2:  frame.stack: []
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:            12: LOAD_CONST 10
           DEBUG:xpython.pyvm2:  frame.stack: [10]
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:            14: STORE_NAME 'x'
           DEBUG:xpython.pyvm2:  frame.stack: []
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:            16: LOAD_CONST None
           DEBUG:xpython.pyvm2:  frame.stack: [None]
           DEBUG:xpython.pyvm2:  blocks     : []
           INFO:xpython.pyvm2:            18: RETURN_VALUE
        
        Status:
        +++++++
        
        Currently only Python 2.5 - 2.7, and 3.2 - 3.7 bytecode is supported.
        Until there is more interest or I get support or funding, I am not
        contemplating expanding to 3.8 and beyond for a while.
        
        A shout out to `xdis <https://pypi.python.org/pypi/xdis>`_ which has
        made cross version interpretation and expanding to other versions
        easier.
        
        Whereas *Byterun* was a bit loose in accepting bytecode opcodes that
        is invalid for particular Python but may be valid for another;
        *x-python* is more stringent. This has pros and cons. On the plus side
        *Byterun* might run certain Python 3.4 bytecode because the opcode
        sets are similar. However starting with Python 3.5 and beyond the
        likelihood gets much less because, while the underlying opcode names
        may be the same, the semantics of the operation may change
        subtely. See for example
        https://github.com/nedbat/byterun/issues/34.
        
        Internally Byterun needs the kind of overhaul we have here to be able
        to scale to support bytecode for more Pythons, and to be able to run
        bytecode across different versions of Python. Specifically, you can't
        rely on Python's `dis <https://docs.python.org/3/library/dis.html>`_
        module if you expect to expect to run a bytecode other than the
        bytecode that the interpreter is running.
        
        In *x-python* there is a clear distinction between the version being
        interpreted and the version of Python that is running. There is
        tighter control of opcodes and an opcode's implementation is kept for
        each Python version. So we'll warn early when something is
        invalid. You can run 3.3 bytecode using Python 3.7 (largely).
        
        The "largely" part is because the interpreter has always made use of
        Python builtins. When a Python version running the interperter matches a
        supported bytecode close enough, the interpreter can (and does) make use
        interpreter internals. For example, built-in functions like `range()`
        are supported this way.
        
        Currently running 2.7 bytecode on 3.x is often not feasible since the
        runtime and internal libraries used like `inspect` are too different.
        
        Over time more of Python's internals may get added so we have better
        cross-version compatability, so that is a possibility. Harder is to
        run later byecode from earlier Python versions. The callenge here is
        that many new features like asynchronous I/O and concurrency
        primatives are not in the older versions and may not easily be
        simulated. However that too is a possibility if there is interest.
        
        You can run many of the tests that Python uses to test itself, and
        those work. Right now this program works best on Python up to 3.4 when
        life in Python was much simpler. It runs over 300 in Python's test
        suite for itself without problems.
        
        Moving back and forward from 3.4 things worse. Python 3.5 is pretty
        good. Python 3.6 and 3.7 is okay but needs work.
        
        
        History
        +++++++
        
        This is a fork of *Byterun.* which is a pure-Python implementation of
        a Python bytecode execution virtual machine.  Net Batchelder started
        it (based on work from Paul Swartz) to get a better understanding of
        bytecodes so he could fix branch coverage bugs in coverage.py.
        
        .. |CircleCI| image:: https://circleci.com/gh/rocky/x-python.svg?style=svg
            :target: https://circleci.com/gh/rocky/x-python
        .. |TravisCI| image:: https://travis-ci.org/rocky/x-python.svg?branch=master
        		 :target: https://travis-ci.org/rocky/x-python
        
        
Platform: UNKNOWN
Classifier: Operating System :: OS Independent
Classifier: Programming Language :: Python :: 2.7
Classifier: Programming Language :: Python :: 3.2
Classifier: Programming Language :: Python :: 3.3
Classifier: Programming Language :: Python :: 3.4
Classifier: Programming Language :: Python :: 3.5
Classifier: Programming Language :: Python :: 3.6
Classifier: Programming Language :: Python :: 3.7
Description-Content-Type: text/x-rst
