The Very High Level Layer

.. highlight:: 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 :c:data:Py_eval_input, :c:data:Py_file_input, :c:data:Py_single_input, and :c:data:Py_func_type_input. These are described following the functions which accept them as parameters.

Note also that several of these functions take :c:expr: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:expr: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 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. If closeit is true, the file is closed before PyRun_SimpleFileExFlags() returns.

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

This is a simplified interface to :c:func:PyRun_SimpleStringFlags below, leaving the :c:struct: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 :c:member:PyConfig.inspect is zero.

.. 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 :term:filesystem encoding and error handler. If closeit is true, the file is closed before PyRun_SimpleFileExFlags() returns.

.. note:: On Windows, fp should be opened as binary mode (e.g. fopen(filename, "rb")). Otherwise, Python may not handle script file with LF line ending correctly.

.. c:function:: int PyRun_InteractiveOneObject(FILE *fp, PyObject *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 must be a Python :class:str object.

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_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)

Similar to :c:func:PyRun_InteractiveOneObject, but filename is a :c:expr:const char*, which is decoded from the :term:filesystem encoding and error handler.

.. 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 :term:filesystem encoding and error handler. Returns 0 at EOF or a negative number upon failure.

.. 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 :file:Modules/_tkinter.c in the Python source code.

.. versionchanged:: 3.12 This function is only called from the :ref:main interpreter <sub-interpreter-support>.

.. 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.

.. versionchanged:: 3.12 This function is only called from the :ref:main interpreter <sub-interpreter-support>.

.. 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 objects globals and locals with the compiler flags specified by flags. globals must be a dictionary; locals can be any object that implements the mapping protocol. The parameter start specifies the start symbol and must be one of the :ref:available start symbols <start-symbols>.

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 :term:filesystem encoding and error handler. 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 symbol is given by start; this can be used to constrain the code which can be compiled and should be :ref:available start symbols <start-symbols>. 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_CompileStringObject, but filename is a byte string decoded from the :term:filesystem encoding and error handler.

.. 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 global and local variables. The other arguments are set to NULL.

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

Evaluate a precompiled code object, given a particular environment for its evaluation. This environment consists of a dictionary of global variables, a mapping object of local variables, arrays of arguments, keywords and defaults, a dictionary of default values for :ref:keyword-only <keyword-only_parameter> arguments and a closure tuple of cells.

.. 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. 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: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, :c:member:~PyCompilerFlags.cf_flags is treated as equal to 0, and any modification due to from __future__ import is discarded.

.. c:member:: int cf_flags

  Compiler flags.

.. c:member:: int cf_feature_version

  *cf_feature_version* is the minor Python version. It should be
  initialized to ``PY_MINOR_VERSION``.

  The field is ignored by default, it is used if and only if
  ``PyCF_ONLY_AST`` flag is set in :c:member:`~PyCompilerFlags.cf_flags`.

.. versionchanged:: 3.8 Added cf_feature_version field.

The available compiler flags are accessible as macros:

.. c:namespace:: NULL

.. c:macro:: PyCF_ALLOW_TOP_LEVEL_AWAIT PyCF_ONLY_AST PyCF_OPTIMIZED_AST PyCF_TYPE_COMMENTS

  See :ref:`compiler flags <ast-compiler-flags>` in documentation of the
  :py:mod:`!ast` Python module, which exports these constants under
  the same names.

The "PyCF" flags above can be combined with "CO_FUTURE" flags such as :c:macro:CO_FUTURE_ANNOTATIONS to enable features normally selectable using :ref:future statements <future>. See :ref:c_codeobject_flags for a complete list.

.. _start-symbols:

Available start symbols ^^^^^^^^^^^^^^^^^^^^^^^

.. c:var:: int Py_eval_input

.. index:: single: Py_CompileString (C function)

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 (C function)

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 (C function)

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:var:: int Py_func_type_input

.. index:: single: Py_CompileString (C function)

The start symbol from the Python grammar for a function type; for use with :c:func:Py_CompileString. This is used to parse "signature type comments" from :pep:484.

This requires the :c:macro:PyCF_ONLY_AST flag to be set.

.. seealso:: * :py:class:ast.FunctionType * :pep:484

.. versionadded:: 3.8

Stack Effects ^^^^^^^^^^^^^

.. seealso:: :py:func:dis.stack_effect

.. c:macro:: PY_INVALID_STACK_EFFECT

Sentinel value representing an invalid stack effect.

This is currently equivalent to INT_MAX.

.. versionadded:: 3.8

.. c:function:: int PyCompile_OpcodeStackEffect(int opcode, int oparg)

Compute the stack effect of opcode with argument oparg.

On success, this function returns the stack effect; on failure, this returns :c:macro:PY_INVALID_STACK_EFFECT.

.. versionadded:: 3.4

.. c:function:: int PyCompile_OpcodeStackEffectWithJump(int opcode, int oparg, int jump)

Similar to :c:func:PyCompile_OpcodeStackEffect, but don't include the stack effect of jumping if jump is zero.

If jump is 0, this will not include the stack effect of jumping, but if jump is 1 or -1, this will include it.

On success, this function returns the stack effect; on failure, this returns :c:macro:PY_INVALID_STACK_EFFECT.

.. versionadded:: 3.8