Python 3.6.5 Documentation >  The Very High Level Layer

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 or a negative number upon failure.

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 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 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_CompileStringObject()", 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 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 *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 keyword-only arguments and a closure tuple of cells.

PyFrameObject

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

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**.