cpython/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, wchar_t **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 (converted to wchar_t according to the user's locale).  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 (i.e., 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`.  *filename* is decoded from the filesystem
   encoding (:func:`sys.getfilesystemencoding`).  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_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, it is decoded from the filesystem encoding
   (:func:`sys.getfilesystemencoding`).  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``.  *filename* is decoded from the
   filesystem encoding (:func:`sys.getfilesystemencoding`).

   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``.  *filename* is decoded from the filesystem encoding
   (:func:`sys.getfilesystemencoding`).  Returns ``0`` at EOF.


.. c:var:: int (*PyOS_InputHook)(void)

   Can be set to point to a function with the prototype
   ``int func(void)``.  The function will be called when Python's
   interpreter prompt is about to become idle and wait for user input
   from the terminal.  The return value is ignored.  Overriding this
   hook can be used to integrate the interpreter's prompt with other
   event loops, as done in the :file:`Modules/_tkinter.c` in the
   Python source code.


.. c:var:: char* (*PyOS_ReadlineFunctionPointer)(FILE *, FILE *, const char *)

   Can be set to point to a function with the prototype
   ``char *func(FILE *stdin, FILE *stdout, char *prompt)``,
   overriding the default function used to read a single line of input
   at the interpreter's prompt.  The function is expected to output
   the string *prompt* if it's not *NULL*, and then read a line of
   input from the provided standard input file, returning the
   resulting string.  For example, The :mod:`readline` module sets
   this hook to provide line-editing and tab-completion features.

   The result must be a string allocated by :c:func:`PyMem_RawMalloc` or
   :c:func:`PyMem_RawRealloc`, or *NULL* if an error occurred.

   .. versionchanged:: 3.4
      The result must be allocated by :c:func:`PyMem_RawMalloc` or
      :c:func:`PyMem_RawRealloc`, instead of being allocated by
      :c:func:`PyMem_Malloc` or :c:func:`PyMem_Realloc`.


.. 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. *filename* is decoded from the filesystem encoding
   (:func:`sys.getfilesystemencoding`).


.. 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,
   it is decoded from the filesystem encoding (:func:`sys.getfilesystemencoding`).
   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)

   This is a simplified interface to :c:func:`Py_CompileStringExFlags` below, with
   *optimize* set to ``-1``.


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

   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.

   The integer *optimize* specifies the optimization level of the compiler; a
   value of ``-1`` selects the optimization level of the interpreter as given by
   :option:`-O` options.  Explicit levels are ``0`` (no optimization;
   ``__debug__`` is true), ``1`` (asserts are removed, ``__debug__`` is false)
   or ``2`` (docstrings are removed too).

   .. versionadded:: 3.4


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

   Like :c:func:`Py_CompileStringExFlags`, but *filename* is a byte string
   decoded from the filesystem encoding (:func:`os.fsdecode`).

   .. versionadded:: 3.2

.. c:function:: PyObject* PyEval_EvalCode(PyObject *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(PyObject *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:type:: PyFrameObject

   The C structure of the objects used to describe frame objects. The
   fields of this type are subject to change at any time.


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

   Evaluate an execution frame.  This is a simplified interface to
   :c:func:`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.

   .. versionchanged:: 3.4
      This function now includes a debug assertion to help ensure that it
      does not silently discard an active exception.


.. 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`.