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185 lines
7.6 KiB
185 lines
7.6 KiB
:mod:`code` --- Interpreter base classes
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========================================
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.. module:: code
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:synopsis: Facilities to implement read-eval-print loops.
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**Source code:** :source:`Lib/code.py`
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--------------
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The ``code`` module provides facilities to implement read-eval-print loops in
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Python. Two classes and convenience functions are included which can be used to
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build applications which provide an interactive interpreter prompt.
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.. class:: InteractiveInterpreter(locals=None)
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This class deals with parsing and interpreter state (the user's namespace); it
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does not deal with input buffering or prompting or input file naming (the
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filename is always passed in explicitly). The optional *locals* argument
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specifies the dictionary in which code will be executed; it defaults to a newly
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created dictionary with key ``'__name__'`` set to ``'__console__'`` and key
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``'__doc__'`` set to ``None``.
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.. class:: InteractiveConsole(locals=None, filename="<console>")
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Closely emulate the behavior of the interactive Python interpreter. This class
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builds on :class:`InteractiveInterpreter` and adds prompting using the familiar
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``sys.ps1`` and ``sys.ps2``, and input buffering.
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.. function:: interact(banner=None, readfunc=None, local=None, exitmsg=None)
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Convenience function to run a read-eval-print loop. This creates a new
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instance of :class:`InteractiveConsole` and sets *readfunc* to be used as
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the :meth:`InteractiveConsole.raw_input` method, if provided. If *local* is
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provided, it is passed to the :class:`InteractiveConsole` constructor for
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use as the default namespace for the interpreter loop. The :meth:`interact`
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method of the instance is then run with *banner* and *exitmsg* passed as the
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banner and exit message to use, if provided. The console object is discarded
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after use.
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.. versionchanged:: 3.6
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Added *exitmsg* parameter.
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.. function:: compile_command(source, filename="<input>", symbol="single")
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This function is useful for programs that want to emulate Python's interpreter
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main loop (a.k.a. the read-eval-print loop). The tricky part is to determine
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when the user has entered an incomplete command that can be completed by
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entering more text (as opposed to a complete command or a syntax error). This
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function *almost* always makes the same decision as the real interpreter main
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loop.
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*source* is the source string; *filename* is the optional filename from which
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source was read, defaulting to ``'<input>'``; and *symbol* is the optional
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grammar start symbol, which should be ``'single'`` (the default), ``'eval'``
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or ``'exec'``.
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Returns a code object (the same as ``compile(source, filename, symbol)``) if the
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command is complete and valid; ``None`` if the command is incomplete; raises
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:exc:`SyntaxError` if the command is complete and contains a syntax error, or
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raises :exc:`OverflowError` or :exc:`ValueError` if the command contains an
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invalid literal.
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.. _interpreter-objects:
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Interactive Interpreter Objects
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-------------------------------
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.. method:: InteractiveInterpreter.runsource(source, filename="<input>", symbol="single")
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Compile and run some source in the interpreter. Arguments are the same as for
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:func:`compile_command`; the default for *filename* is ``'<input>'``, and for
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*symbol* is ``'single'``. One of several things can happen:
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* The input is incorrect; :func:`compile_command` raised an exception
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(:exc:`SyntaxError` or :exc:`OverflowError`). A syntax traceback will be
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printed by calling the :meth:`showsyntaxerror` method. :meth:`runsource`
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returns ``False``.
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* The input is incomplete, and more input is required; :func:`compile_command`
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returned ``None``. :meth:`runsource` returns ``True``.
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* The input is complete; :func:`compile_command` returned a code object. The
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code is executed by calling the :meth:`runcode` (which also handles run-time
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exceptions, except for :exc:`SystemExit`). :meth:`runsource` returns ``False``.
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The return value can be used to decide whether to use ``sys.ps1`` or ``sys.ps2``
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to prompt the next line.
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.. method:: InteractiveInterpreter.runcode(code)
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Execute a code object. When an exception occurs, :meth:`showtraceback` is called
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to display a traceback. All exceptions are caught except :exc:`SystemExit`,
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which is allowed to propagate.
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A note about :exc:`KeyboardInterrupt`: this exception may occur elsewhere in
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this code, and may not always be caught. The caller should be prepared to deal
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with it.
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.. method:: InteractiveInterpreter.showsyntaxerror(filename=None)
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Display the syntax error that just occurred. This does not display a stack
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trace because there isn't one for syntax errors. If *filename* is given, it is
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stuffed into the exception instead of the default filename provided by Python's
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parser, because it always uses ``'<string>'`` when reading from a string. The
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output is written by the :meth:`write` method.
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.. method:: InteractiveInterpreter.showtraceback()
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Display the exception that just occurred. We remove the first stack item
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because it is within the interpreter object implementation. The output is
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written by the :meth:`write` method.
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.. versionchanged:: 3.5 The full chained traceback is displayed instead
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of just the primary traceback.
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.. method:: InteractiveInterpreter.write(data)
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Write a string to the standard error stream (``sys.stderr``). Derived classes
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should override this to provide the appropriate output handling as needed.
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.. _console-objects:
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Interactive Console Objects
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---------------------------
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The :class:`InteractiveConsole` class is a subclass of
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:class:`InteractiveInterpreter`, and so offers all the methods of the
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interpreter objects as well as the following additions.
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.. method:: InteractiveConsole.interact(banner=None, exitmsg=None)
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Closely emulate the interactive Python console. The optional *banner* argument
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specify the banner to print before the first interaction; by default it prints a
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banner similar to the one printed by the standard Python interpreter, followed
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by the class name of the console object in parentheses (so as not to confuse
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this with the real interpreter -- since it's so close!).
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The optional *exitmsg* argument specifies an exit message printed when exiting.
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Pass the empty string to suppress the exit message. If *exitmsg* is not given or
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``None``, a default message is printed.
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.. versionchanged:: 3.4
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To suppress printing any banner, pass an empty string.
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.. versionchanged:: 3.6
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Print an exit message when exiting.
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.. method:: InteractiveConsole.push(line)
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Push a line of source text to the interpreter. The line should not have a
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trailing newline; it may have internal newlines. The line is appended to a
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buffer and the interpreter's :meth:`runsource` method is called with the
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concatenated contents of the buffer as source. If this indicates that the
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command was executed or invalid, the buffer is reset; otherwise, the command is
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incomplete, and the buffer is left as it was after the line was appended. The
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return value is ``True`` if more input is required, ``False`` if the line was
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dealt with in some way (this is the same as :meth:`runsource`).
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.. method:: InteractiveConsole.resetbuffer()
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Remove any unhandled source text from the input buffer.
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.. method:: InteractiveConsole.raw_input(prompt="")
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Write a prompt and read a line. The returned line does not include the trailing
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newline. When the user enters the EOF key sequence, :exc:`EOFError` is raised.
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The base implementation reads from ``sys.stdin``; a subclass may replace this
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with a different implementation.
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