/Doc/library/code.rst

  1
  2:mod:`code` --- Interpreter base classes
  3========================================
  4
  5.. module:: code
  6   :synopsis: Facilities to implement read-eval-print loops.
  7
  8
  9
 10The ``code`` module provides facilities to implement read-eval-print loops in
 11Python.  Two classes and convenience functions are included which can be used to
 12build applications which provide an interactive interpreter prompt.
 13
 14
 15.. class:: InteractiveInterpreter([locals])
 16
 17   This class deals with parsing and interpreter state (the user's namespace); it
 18   does not deal with input buffering or prompting or input file naming (the
 19   filename is always passed in explicitly). The optional *locals* argument
 20   specifies the dictionary in which code will be executed; it defaults to a newly
 21   created dictionary with key ``'__name__'`` set to ``'__console__'`` and key
 22   ``'__doc__'`` set to ``None``.
 23
 24
 25.. class:: InteractiveConsole([locals[, filename]])
 26
 27   Closely emulate the behavior of the interactive Python interpreter. This class
 28   builds on :class:`InteractiveInterpreter` and adds prompting using the familiar
 29   ``sys.ps1`` and ``sys.ps2``, and input buffering.
 30
 31
 32.. function:: interact([banner[, readfunc[, local]]])
 33
 34   Convenience function to run a read-eval-print loop.  This creates a new instance
 35   of :class:`InteractiveConsole` and sets *readfunc* to be used as the
 36   :meth:`raw_input` method, if provided.  If *local* is provided, it is passed to
 37   the :class:`InteractiveConsole` constructor for use as the default namespace for
 38   the interpreter loop.  The :meth:`interact` method of the instance is then run
 39   with *banner* passed as the banner to use, if provided.  The console object is
 40   discarded after use.
 41
 42
 43.. function:: compile_command(source[, filename[, symbol]])
 44
 45   This function is useful for programs that want to emulate Python's interpreter
 46   main loop (a.k.a. the read-eval-print loop).  The tricky part is to determine
 47   when the user has entered an incomplete command that can be completed by
 48   entering more text (as opposed to a complete command or a syntax error).  This
 49   function *almost* always makes the same decision as the real interpreter main
 50   loop.
 51
 52   *source* is the source string; *filename* is the optional filename from which
 53   source was read, defaulting to ``'<input>'``; and *symbol* is the optional
 54   grammar start symbol, which should be either ``'single'`` (the default) or
 55   ``'eval'``.
 56
 57   Returns a code object (the same as ``compile(source, filename, symbol)``) if the
 58   command is complete and valid; ``None`` if the command is incomplete; raises
 59   :exc:`SyntaxError` if the command is complete and contains a syntax error, or
 60   raises :exc:`OverflowError` or :exc:`ValueError` if the command contains an
 61   invalid literal.
 62
 63
 64.. _interpreter-objects:
 65
 66Interactive Interpreter Objects
 67-------------------------------
 68
 69
 70.. method:: InteractiveInterpreter.runsource(source[, filename[, symbol]])
 71
 72   Compile and run some source in the interpreter. Arguments are the same as for
 73   :func:`compile_command`; the default for *filename* is ``'<input>'``, and for
 74   *symbol* is ``'single'``.  One several things can happen:
 75
 76   * The input is incorrect; :func:`compile_command` raised an exception
 77     (:exc:`SyntaxError` or :exc:`OverflowError`).  A syntax traceback will be
 78     printed by calling the :meth:`showsyntaxerror` method.  :meth:`runsource`
 79     returns ``False``.
 80
 81   * The input is incomplete, and more input is required; :func:`compile_command`
 82     returned ``None``. :meth:`runsource` returns ``True``.
 83
 84   * The input is complete; :func:`compile_command` returned a code object.  The
 85     code is executed by calling the :meth:`runcode` (which also handles run-time
 86     exceptions, except for :exc:`SystemExit`). :meth:`runsource` returns ``False``.
 87
 88   The return value can be used to decide whether to use ``sys.ps1`` or ``sys.ps2``
 89   to prompt the next line.
 90
 91
 92.. method:: InteractiveInterpreter.runcode(code)
 93
 94   Execute a code object. When an exception occurs, :meth:`showtraceback` is called
 95   to display a traceback.  All exceptions are caught except :exc:`SystemExit`,
 96   which is allowed to propagate.
 97
 98   A note about :exc:`KeyboardInterrupt`: this exception may occur elsewhere in
 99   this code, and may not always be caught.  The caller should be prepared to deal
100   with it.
101
102
103.. method:: InteractiveInterpreter.showsyntaxerror([filename])
104
105   Display the syntax error that just occurred.  This does not display a stack
106   trace because there isn't one for syntax errors. If *filename* is given, it is
107   stuffed into the exception instead of the default filename provided by Python's
108   parser, because it always uses ``'<string>'`` when reading from a string. The
109   output is written by the :meth:`write` method.
110
111
112.. method:: InteractiveInterpreter.showtraceback()
113
114   Display the exception that just occurred.  We remove the first stack item
115   because it is within the interpreter object implementation. The output is
116   written by the :meth:`write` method.
117
118
119.. method:: InteractiveInterpreter.write(data)
120
121   Write a string to the standard error stream (``sys.stderr``). Derived classes
122   should override this to provide the appropriate output handling as needed.
123
124
125.. _console-objects:
126
127Interactive Console Objects
128---------------------------
129
130The :class:`InteractiveConsole` class is a subclass of
131:class:`InteractiveInterpreter`, and so offers all the methods of the
132interpreter objects as well as the following additions.
133
134
135.. method:: InteractiveConsole.interact([banner])
136
137   Closely emulate the interactive Python console. The optional banner argument
138   specify the banner to print before the first interaction; by default it prints a
139   banner similar to the one printed by the standard Python interpreter, followed
140   by the class name of the console object in parentheses (so as not to confuse
141   this with the real interpreter -- since it's so close!).
142
143
144.. method:: InteractiveConsole.push(line)
145
146   Push a line of source text to the interpreter. The line should not have a
147   trailing newline; it may have internal newlines.  The line is appended to a
148   buffer and the interpreter's :meth:`runsource` method is called with the
149   concatenated contents of the buffer as source.  If this indicates that the
150   command was executed or invalid, the buffer is reset; otherwise, the command is
151   incomplete, and the buffer is left as it was after the line was appended.  The
152   return value is ``True`` if more input is required, ``False`` if the line was
153   dealt with in some way (this is the same as :meth:`runsource`).
154
155
156.. method:: InteractiveConsole.resetbuffer()
157
158   Remove any unhandled source text from the input buffer.
159
160
161.. method:: InteractiveConsole.raw_input([prompt])
162
163   Write a prompt and read a line.  The returned line does not include the trailing
164   newline.  When the user enters the EOF key sequence, :exc:`EOFError` is raised.
165   The base implementation uses the built-in function :func:`raw_input`; a subclass
166   may replace this with a different implementation.
167