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 Py_eval_input, Py_file_input, and Py_single_input. These are described following the functions which accept them as parameters.

Note also that several of these functions take FILE* parameters. One particular issue which needs to be handled carefully is that the 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 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.

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 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 SystemExit is raised, this function will not return 1, but exit the process, as long as Py_InspectFlag is not set.

int PyRun_AnyFile(FILE *fp, const char *filename)

This is a simplified interface to PyRun_AnyFileExFlags() below, leaving closeit set to 0 and flags set to NULL.

int PyRun_AnyFileFlags(FILE *fp, const char *filename, PyCompilerFlags *flags)

This is a simplified interface to PyRun_AnyFileExFlags() below, leaving the closeit argument set to 0.

int PyRun_AnyFileEx(FILE *fp, const char *filename, int closeit)

This is a simplified interface to PyRun_AnyFileExFlags() below, leaving the flags argument set to NULL.

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 PyRun_InteractiveLoop(), otherwise return the result of PyRun_SimpleFile(). filename is decoded from the filesystem encoding (sys.getfilesystemencoding()). If filename is NULL, this function uses "???" as the filename.

int PyRun_SimpleString(const char *command)

This is a simplified interface to PyRun_SimpleStringFlags() below, leaving the PyCompilerFlags* argument set to NULL.

int PyRun_SimpleStringFlags(const char *command, PyCompilerFlags *flags)

Executes the Python source code from command in the __main__ module according to the flags argument. If __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 SystemExit is raised, this function will not return -1, but exit the process, as long as Py_InspectFlag is not set.

int PyRun_SimpleFile(FILE *fp, const char *filename)

This is a simplified interface to PyRun_SimpleFileExFlags() below, leaving closeit set to 0 and flags set to NULL.

int PyRun_SimpleFileEx(FILE *fp, const char *filename, int closeit)

This is a simplified interface to PyRun_SimpleFileExFlags() below, leaving flags set to NULL.

int PyRun_SimpleFileExFlags(FILE *fp, const char *filename, int closeit, PyCompilerFlags *flags)

Similar to 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 (sys.getfilesystemencoding()). If closeit is true, the file is closed before PyRun_SimpleFileExFlags returns.

int PyRun_InteractiveOne(FILE *fp, const char *filename)

This is a simplified interface to PyRun_InteractiveOneFlags() below, leaving flags set to NULL.

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 (sys.getfilesystemencoding()).

Returns 0 when the input was executed successfully, -1 if there was an exception, or an error code from the errcode.h include file distributed as part of Python if there was a parse error. (Note that errcode.h is not included by Python.h, so must be included specifically if needed.)

int PyRun_InteractiveLoop(FILE *fp, const char *filename)

This is a simplified interface to PyRun_InteractiveLoopFlags() below, leaving flags set to NULL.

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 (sys.getfilesystemencoding()). Returns 0 at EOF.

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 Modules/_tkinter.c in the Python source code.

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 readline module sets this hook to provide line-editing and tab-completion features.

The result must be a string allocated by PyMem_RawMalloc() or PyMem_RawRealloc(), or NULL if an error occurred.

Changed in version 3.4: The result must be allocated by PyMem_RawMalloc() or PyMem_RawRealloc(), instead of being allocated by PyMem_Malloc() or PyMem_Realloc().

struct _node* PyParser_SimpleParseString(const char *str, int start)

This is a simplified interface to PyParser_SimpleParseStringFlagsFilename() below, leaving filename set to NULL and flags set to 0.

struct _node* PyParser_SimpleParseStringFlags(const char *str, int start, int flags)

This is a simplified interface to PyParser_SimpleParseStringFlagsFilename() below, leaving filename set to NULL.

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 (sys.getfilesystemencoding()).

struct _node* PyParser_SimpleParseFile(FILE *fp, const char *filename, int start)

This is a simplified interface to PyParser_SimpleParseFileFlags() below, leaving flags set to 0.

struct _node* PyParser_SimpleParseFileFlags(FILE *fp, const char *filename, int start, int flags)

Similar to PyParser_SimpleParseStringFlagsFilename(), but the Python source code is read from fp instead of an in-memory string.

PyObject* PyRun_String(const char *str, int start, PyObject *globals, PyObject *locals)

Return value: New reference.

This is a simplified interface to PyRun_StringFlags() below, leaving flags set to NULL.

PyObject* PyRun_StringFlags(const char *str, int start, PyObject *globals, PyObject *locals, PyCompilerFlags *flags)

Return value: New reference.

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.

PyObject* PyRun_File(FILE *fp, const char *filename, int start, PyObject *globals, PyObject *locals)

Return value: New reference.

This is a simplified interface to PyRun_FileExFlags() below, leaving closeit set to 0 and flags set to NULL.

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

Return value: New reference.

This is a simplified interface to PyRun_FileExFlags() below, leaving flags set to NULL.

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

Return value: New reference.

This is a simplified interface to PyRun_FileExFlags() below, leaving closeit set to 0.

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

Return value: New reference.

Similar to 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 (sys.getfilesystemencoding()). If closeit is true, the file is closed before PyRun_FileExFlags() returns.

PyObject* Py_CompileString(const char *str, const char *filename, int start)

Return value: New reference.

This is a simplified interface to Py_CompileStringFlags() below, leaving flags set to NULL.

PyObject* Py_CompileStringFlags(const char *str, const char *filename, int start, PyCompilerFlags *flags)

Return value: New reference.

This is a simplified interface to Py_CompileStringExFlags() below, with optimize set to -1.

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 Py_eval_input, Py_file_input, or Py_single_input. The filename specified by filename is used to construct the code object and may appear in tracebacks or 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 -O options. Explicit levels are 0 (no optimization; __debug__ is true), 1 (asserts are removed, __debug__ is false) or 2 (docstrings are removed too).

New in version 3.4.

PyObject* Py_CompileStringExFlags(const char *str, const char *filename, int start, PyCompilerFlags *flags, int optimize)

Like Py_CompileStringExFlags(), but filename is a byte string decoded from the filesystem encoding (os.fsdecode()).

New in version 3.2.

PyObject* PyEval_EvalCode(PyObject *co, PyObject *globals, PyObject *locals)

Return value: New reference.

This is a simplified interface to PyEval_EvalCodeEx(), with just the code object, and the dictionaries of global and local variables. The other arguments are set to NULL.

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.

PyObject* PyEval_EvalFrame(PyFrameObject *f)

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

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 throw() methods of generator objects.

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

int PyEval_MergeCompilerFlags(PyCompilerFlags *cf)

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

int Py_eval_input

The start symbol from the Python grammar for isolated expressions; for use with Py_CompileString().

int Py_file_input

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

int Py_single_input

The start symbol from the Python grammar for a single statement; for use with Py_CompileString(). This is the symbol used for the interactive interpreter loop.

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, cf_flags is treated as equal to 0, and any modification due to from __future__ import is discarded.

struct PyCompilerFlags {
    int cf_flags;
}

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.