Python 3.6.5 Documentation >  "code" — Interpreter base classes

"code" — Interpreter base classes
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**Source code:** Lib/code.py

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The "code" module provides facilities to implement read-eval-print
loops in Python. Two classes and convenience functions are included
which can be used to build applications which provide an interactive
interpreter prompt.

class code.InteractiveInterpreter(locals=None)

This class deals with parsing and interpreter state (the user’s
namespace); it does not deal with input buffering or prompting or
input file naming (the filename is always passed in explicitly).
The optional *locals* argument specifies the dictionary in which
code will be executed; it defaults to a newly created dictionary
with key "'__name__'" set to "'__console__'" and key "'__doc__'"
set to "None".

class code.InteractiveConsole(locals=None, filename="<console>")

Closely emulate the behavior of the interactive Python interpreter.
This class builds on "InteractiveInterpreter" and adds prompting
using the familiar "sys.ps1" and "sys.ps2", and input buffering.

code.interact(banner=None, readfunc=None, local=None, exitmsg=None)

Convenience function to run a read-eval-print loop. This creates a
new instance of "InteractiveConsole" and sets *readfunc* to be used
as the "InteractiveConsole.raw_input()" method, if provided. If
*local* is provided, it is passed to the "InteractiveConsole"
constructor for use as the default namespace for the interpreter
loop. The "interact()" method of the instance is then run with
*banner* and *exitmsg* passed as the banner and exit message to
use, if provided. The console object is discarded after use.

Changed in version 3.6: Added *exitmsg* parameter.

code.compile_command(source, filename="<input>", symbol="single")

This function is useful for programs that want to emulate Python’s
interpreter main loop (a.k.a. the read-eval-print loop). The
tricky part is to determine when the user has entered an incomplete
command that can be completed by entering more text (as opposed to
a complete command or a syntax error). This function *almost*
always makes the same decision as the real interpreter main loop.

*source* is the source string; *filename* is the optional filename
from which source was read, defaulting to "'<input>'"; and *symbol*
is the optional grammar start symbol, which should be either
"'single'" (the default) or "'eval'".

Returns a code object (the same as "compile(source, filename,
symbol)") if the command is complete and valid; "None" if the
command is incomplete; raises "SyntaxError" if the command is
complete and contains a syntax error, or raises "OverflowError" or
"ValueError" if the command contains an invalid literal.

Interactive Interpreter Objects
===============================

InteractiveInterpreter.runsource(source, filename="<input>", symbol="single")

Compile and run some source in the interpreter. Arguments are the
same as for "compile_command()"; the default for *filename* is
"'<input>'", and for *symbol* is "'single'". One several things
can happen:

* The input is incorrect; "compile_command()" raised an exception
("SyntaxError" or "OverflowError"). A syntax traceback will be
printed by calling the "showsyntaxerror()" method. "runsource()"
returns "False".

* The input is incomplete, and more input is required;
"compile_command()" returned "None". "runsource()" returns
"True".

* The input is complete; "compile_command()" returned a code
object. The code is executed by calling the "runcode()" (which
also handles run-time exceptions, except for "SystemExit").
"runsource()" returns "False".

The return value can be used to decide whether to use "sys.ps1" or
"sys.ps2" to prompt the next line.

InteractiveInterpreter.runcode(code)

Execute a code object. When an exception occurs, "showtraceback()"
is called to display a traceback. All exceptions are caught except
"SystemExit", which is allowed to propagate.

A note about "KeyboardInterrupt": this exception may occur
elsewhere in this code, and may not always be caught. The caller
should be prepared to deal with it.

InteractiveInterpreter.showsyntaxerror(filename=None)

Display the syntax error that just occurred. This does not display
a stack trace because there isn’t one for syntax errors. If
*filename* is given, it is stuffed into the exception instead of
the default filename provided by Python’s parser, because it always
uses "'<string>'" when reading from a string. The output is written
by the "write()" method.

InteractiveInterpreter.showtraceback()

Display the exception that just occurred. We remove the first
stack item because it is within the interpreter object
implementation. The output is written by the "write()" method.

Changed in version 3.5: The full chained traceback is displayed
instead of just the primary traceback.

InteractiveInterpreter.write(data)

Write a string to the standard error stream ("sys.stderr"). Derived
classes should override this to provide the appropriate output
handling as needed.

Interactive Console Objects
===========================

The "InteractiveConsole" class is a subclass of
"InteractiveInterpreter", and so offers all the methods of the
interpreter objects as well as the following additions.

InteractiveConsole.interact(banner=None, exitmsg=None)

Closely emulate the interactive Python console. The optional
*banner* argument specify the banner to print before the first
interaction; by default it prints a banner similar to the one
printed by the standard Python interpreter, followed by the class
name of the console object in parentheses (so as not to confuse
this with the real interpreter – since it’s so close!).

The optional *exitmsg* argument specifies an exit message printed
when exiting. Pass the empty string to suppress the exit message.
If *exitmsg* is not given or "None", a default message is printed.

Changed in version 3.4: To suppress printing any banner, pass an
empty string.

Changed in version 3.6: Print an exit message when exiting.

InteractiveConsole.push(line)

Push a line of source text to the interpreter. The line should not
have a trailing newline; it may have internal newlines. The line
is appended to a buffer and the interpreter’s "runsource()" method
is called with the concatenated contents of the buffer as source.
If this indicates that the command was executed or invalid, the
buffer is reset; otherwise, the command is incomplete, and the
buffer is left as it was after the line was appended. The return
value is "True" if more input is required, "False" if the line was
dealt with in some way (this is the same as "runsource()").

InteractiveConsole.resetbuffer()

Remove any unhandled source text from the input buffer.

InteractiveConsole.raw_input(prompt="")

Write a prompt and read a line. The returned line does not include
the trailing newline. When the user enters the EOF key sequence,
"EOFError" is raised. The base implementation reads from
"sys.stdin"; a subclass may replace this with a different
implementation.