source: python/trunk/Doc/c-api/veryhigh.rst

.. highlightlang:: c


.. _veryhigh:

*************************
The Very High Level Layer
*************************

The functions in this chapter will let you execute Python source code given in a
file or a buffer, but they will not let you interact in a more detailed way with
the interpreter.

Several of these functions accept a start symbol from the grammar as a
parameter.  The available start symbols are :const:`Py_eval_input`,
:const:`Py_file_input`, and :const:`Py_single_input`.  These are described
following the functions which accept them as parameters.

Note also that several of these functions take :c:type:`FILE\*` parameters.  One
particular issue which needs to be handled carefully is that the :c:type:`FILE`
structure for different C libraries can be different and incompatible.  Under
Windows (at least), it is possible for dynamically linked extensions to actually
use different libraries, so care should be taken that :c:type:`FILE\*` parameters
are only passed to these functions if it is certain that they were created by
the same library that the Python runtime is using.


.. c:function:: int Py_Main(int argc, char **argv)

   The main program for the standard interpreter.  This is made available for
   programs which embed Python.  The *argc* and *argv* parameters should be
   prepared exactly as those which are passed to a C program's :c:func:`main`
   function.  It is important to note that the argument list may be modified (but
   the contents of the strings pointed to by the argument list are not). The return
   value will be ``0`` if the interpreter exits normally (ie, without an
   exception), ``1`` if the interpreter exits due to an exception, or ``2``
   if the parameter list does not represent a valid Python command line.

   Note that if an otherwise unhandled :exc:`SystemExit` is raised, this
   function will not return ``1``, but exit the process, as long as
   ``Py_InspectFlag`` is not set.


.. c:function:: int PyRun_AnyFile(FILE *fp, const char *filename)

   This is a simplified interface to :c:func:`PyRun_AnyFileExFlags` below, leaving
   *closeit* set to ``0`` and *flags* set to *NULL*.


.. c:function:: int PyRun_AnyFileFlags(FILE *fp, const char *filename, PyCompilerFlags *flags)

   This is a simplified interface to :c:func:`PyRun_AnyFileExFlags` below, leaving
   the *closeit* argument set to ``0``.


.. c:function:: int PyRun_AnyFileEx(FILE *fp, const char *filename, int closeit)

   This is a simplified interface to :c:func:`PyRun_AnyFileExFlags` below, leaving
   the *flags* argument set to *NULL*.


.. c:function:: int PyRun_AnyFileExFlags(FILE *fp, const char *filename, int closeit, PyCompilerFlags *flags)

   If *fp* refers to a file associated with an interactive device (console or
   terminal input or Unix pseudo-terminal), return the value of
   :c:func:`PyRun_InteractiveLoop`, otherwise return the result of
   :c:func:`PyRun_SimpleFile`.  If *filename* is *NULL*, this function uses
   ``"???"`` as the filename.


.. c:function:: int PyRun_SimpleString(const char *command)

   This is a simplified interface to :c:func:`PyRun_SimpleStringFlags` below,
   leaving the *PyCompilerFlags\** argument set to NULL.


.. c:function:: int PyRun_SimpleStringFlags(const char *command, PyCompilerFlags *flags)

   Executes the Python source code from *command* in the :mod:`__main__` module
   according to the *flags* argument. If :mod:`__main__` does not already exist, it
   is created.  Returns ``0`` on success or ``-1`` if an exception was raised.  If
   there was an error, there is no way to get the exception information. For the
   meaning of *flags*, see below.

   Note that if an otherwise unhandled :exc:`SystemExit` is raised, this
   function will not return ``-1``, but exit the process, as long as
   ``Py_InspectFlag`` is not set.


.. c:function:: int PyRun_SimpleFile(FILE *fp, const char *filename)

   This is a simplified interface to :c:func:`PyRun_SimpleFileExFlags` below,
   leaving *closeit* set to ``0`` and *flags* set to *NULL*.


.. c:function:: int PyRun_SimpleFileFlags(FILE *fp, const char *filename, PyCompilerFlags *flags)

   This is a simplified interface to :c:func:`PyRun_SimpleFileExFlags` below,
   leaving *closeit* set to ``0``.


.. c:function:: int PyRun_SimpleFileEx(FILE *fp, const char *filename, int closeit)

   This is a simplified interface to :c:func:`PyRun_SimpleFileExFlags` below,
   leaving *flags* set to *NULL*.


.. c:function:: int PyRun_SimpleFileExFlags(FILE *fp, const char *filename, int closeit, PyCompilerFlags *flags)

   Similar to :c:func:`PyRun_SimpleStringFlags`, but the Python source code is read
   from *fp* instead of an in-memory string. *filename* should be the name of the
   file.  If *closeit* is true, the file is closed before PyRun_SimpleFileExFlags
   returns.


.. c:function:: int PyRun_InteractiveOne(FILE *fp, const char *filename)

   This is a simplified interface to :c:func:`PyRun_InteractiveOneFlags` below,
   leaving *flags* set to *NULL*.


.. c:function:: int PyRun_InteractiveOneFlags(FILE *fp, const char *filename, PyCompilerFlags *flags)

   Read and execute a single statement from a file associated with an
   interactive device according to the *flags* argument.  The user will be
   prompted using ``sys.ps1`` and ``sys.ps2``.  Returns ``0`` when the input was
   executed successfully, ``-1`` if there was an exception, or an error code
   from the :file:`errcode.h` include file distributed as part of Python if
   there was a parse error.  (Note that :file:`errcode.h` is not included by
   :file:`Python.h`, so must be included specifically if needed.)


.. c:function:: int PyRun_InteractiveLoop(FILE *fp, const char *filename)

   This is a simplified interface to :c:func:`PyRun_InteractiveLoopFlags` below,
   leaving *flags* set to *NULL*.


.. c:function:: int PyRun_InteractiveLoopFlags(FILE *fp, const char *filename, PyCompilerFlags *flags)

   Read and execute statements from a file associated with an interactive device
   until EOF is reached.  The user will be prompted using ``sys.ps1`` and
   ``sys.ps2``.  Returns ``0`` at EOF.


.. c:function:: struct _node* PyParser_SimpleParseString(const char *str, int start)

   This is a simplified interface to
   :c:func:`PyParser_SimpleParseStringFlagsFilename` below, leaving  *filename* set
   to *NULL* and *flags* set to ``0``.


.. c:function:: struct _node* PyParser_SimpleParseStringFlags( const char *str, int start, int flags)

   This is a simplified interface to
   :c:func:`PyParser_SimpleParseStringFlagsFilename` below, leaving  *filename* set
   to *NULL*.


.. c:function:: struct _node* PyParser_SimpleParseStringFlagsFilename( const char *str, const char *filename, int start, int flags)

   Parse Python source code from *str* using the start token *start* according to
   the *flags* argument.  The result can be used to create a code object which can
   be evaluated efficiently. This is useful if a code fragment must be evaluated
   many times.


.. c:function:: struct _node* PyParser_SimpleParseFile(FILE *fp, const char *filename, int start)

   This is a simplified interface to :c:func:`PyParser_SimpleParseFileFlags` below,
   leaving *flags* set to ``0``


.. c:function:: struct _node* PyParser_SimpleParseFileFlags(FILE *fp, const char *filename, int start, int flags)

   Similar to :c:func:`PyParser_SimpleParseStringFlagsFilename`, but the Python
   source code is read from *fp* instead of an in-memory string.


.. c:function:: PyObject* PyRun_String(const char *str, int start, PyObject *globals, PyObject *locals)

   This is a simplified interface to :c:func:`PyRun_StringFlags` below, leaving
   *flags* set to *NULL*.


.. c:function:: PyObject* PyRun_StringFlags(const char *str, int start, PyObject *globals, PyObject *locals, PyCompilerFlags *flags)

   Execute Python source code from *str* in the context specified by the
   dictionaries *globals* and *locals* with the compiler flags specified by
   *flags*.  The parameter *start* specifies the start token that should be used to
   parse the source code.

   Returns the result of executing the code as a Python object, or *NULL* if an
   exception was raised.


.. c:function:: PyObject* PyRun_File(FILE *fp, const char *filename, int start, PyObject *globals, PyObject *locals)

   This is a simplified interface to :c:func:`PyRun_FileExFlags` below, leaving
   *closeit* set to ``0`` and *flags* set to *NULL*.


.. c:function:: PyObject* PyRun_FileEx(FILE *fp, const char *filename, int start, PyObject *globals, PyObject *locals, int closeit)

   This is a simplified interface to :c:func:`PyRun_FileExFlags` below, leaving
   *flags* set to *NULL*.


.. c:function:: PyObject* PyRun_FileFlags(FILE *fp, const char *filename, int start, PyObject *globals, PyObject *locals, PyCompilerFlags *flags)

   This is a simplified interface to :c:func:`PyRun_FileExFlags` below, leaving
   *closeit* set to ``0``.


.. c:function:: PyObject* PyRun_FileExFlags(FILE *fp, const char *filename, int start, PyObject *globals, PyObject *locals, int closeit, PyCompilerFlags *flags)

   Similar to :c:func:`PyRun_StringFlags`, but the Python source code is read from
   *fp* instead of an in-memory string. *filename* should be the name of the file.
   If *closeit* is true, the file is closed before :c:func:`PyRun_FileExFlags`
   returns.


.. c:function:: PyObject* Py_CompileString(const char *str, const char *filename, int start)

   This is a simplified interface to :c:func:`Py_CompileStringFlags` below, leaving
   *flags* set to *NULL*.


.. c:function:: PyObject* Py_CompileStringFlags(const char *str, const char *filename, int start, PyCompilerFlags *flags)

   Parse and compile the Python source code in *str*, returning the resulting code
   object.  The start token is given by *start*; this can be used to constrain the
   code which can be compiled and should be :const:`Py_eval_input`,
   :const:`Py_file_input`, or :const:`Py_single_input`.  The filename specified by
   *filename* is used to construct the code object and may appear in tracebacks or
   :exc:`SyntaxError` exception messages.  This returns *NULL* if the code cannot
   be parsed or compiled.


.. c:function:: PyObject* PyEval_EvalCode(PyCodeObject *co, PyObject *globals, PyObject *locals)

   This is a simplified interface to :c:func:`PyEval_EvalCodeEx`, with just
   the code object, and the dictionaries of global and local variables.
   The other arguments are set to *NULL*.


.. c:function:: PyObject* PyEval_EvalCodeEx(PyCodeObject *co, PyObject *globals, PyObject *locals, PyObject **args, int argcount, PyObject **kws, int kwcount, PyObject **defs, int defcount, PyObject *closure)

   Evaluate a precompiled code object, given a particular environment for its
   evaluation.  This environment consists of dictionaries of global and local
   variables, arrays of arguments, keywords and defaults, and a closure tuple of
   cells.


.. c:function:: PyObject* PyEval_EvalFrame(PyFrameObject *f)

   Evaluate an execution frame.  This is a simplified interface to
   PyEval_EvalFrameEx, for backward compatibility.


.. c:function:: PyObject* PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)

   This is the main, unvarnished function of Python interpretation.  It is
   literally 2000 lines long.  The code object associated with the execution
   frame *f* is executed, interpreting bytecode and executing calls as needed.
   The additional *throwflag* parameter can mostly be ignored - if true, then
   it causes an exception to immediately be thrown; this is used for the
   :meth:`~generator.throw` methods of generator objects.


.. c:function:: int PyEval_MergeCompilerFlags(PyCompilerFlags *cf)

   This function changes the flags of the current evaluation frame, and returns
   true on success, false on failure.


.. c:var:: int Py_eval_input

   .. index:: single: Py_CompileString()

   The start symbol from the Python grammar for isolated expressions; for use with
   :c:func:`Py_CompileString`.


.. c:var:: int Py_file_input

   .. index:: single: Py_CompileString()

   The start symbol from the Python grammar for sequences of statements as read
   from a file or other source; for use with :c:func:`Py_CompileString`.  This is
   the symbol to use when compiling arbitrarily long Python source code.


.. c:var:: int Py_single_input

   .. index:: single: Py_CompileString()

   The start symbol from the Python grammar for a single statement; for use with
   :c:func:`Py_CompileString`. This is the symbol used for the interactive
   interpreter loop.


.. c:type:: struct PyCompilerFlags

   This is the structure used to hold compiler flags.  In cases where code is only
   being compiled, it is passed as ``int flags``, and in cases where code is being
   executed, it is passed as ``PyCompilerFlags *flags``.  In this case, ``from
   __future__ import`` can modify *flags*.

   Whenever ``PyCompilerFlags *flags`` is *NULL*, :attr:`cf_flags` is treated as
   equal to ``0``, and any modification due to ``from __future__ import`` is
   discarded.  ::

      struct PyCompilerFlags {
          int cf_flags;
      }


.. c:var:: int CO_FUTURE_DIVISION

   This bit can be set in *flags* to cause division operator ``/`` to be
   interpreted as "true division" according to :pep:`238`.