2
:mod:`code` --- Interpreter base classes
3
========================================
6
:synopsis: Facilities to implement read-eval-print loops.
10
The ``code`` module provides facilities to implement read-eval-print loops in
11
Python. Two classes and convenience functions are included which can be used to
12
build applications which provide an interactive interpreter prompt.
15
.. class:: InteractiveInterpreter([locals])
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``.
25
.. class:: InteractiveConsole([locals[, filename]])
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.
32
.. function:: interact([banner[, readfunc[, local]]])
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
43
.. function:: compile_command(source[, filename[, symbol]])
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
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
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
64
.. _interpreter-objects:
66
Interactive Interpreter Objects
67
-------------------------------
70
.. method:: InteractiveInterpreter.runsource(source[, filename[, symbol]])
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:
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`
81
* The input is incomplete, and more input is required; :func:`compile_command`
82
returned ``None``. :meth:`runsource` returns ``True``.
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``.
88
The return value can be used to decide whether to use ``sys.ps1`` or ``sys.ps2``
89
to prompt the next line.
92
.. method:: InteractiveInterpreter.runcode(code)
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.
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
103
.. method:: InteractiveInterpreter.showsyntaxerror([filename])
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.
112
.. method:: InteractiveInterpreter.showtraceback()
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.
119
.. method:: InteractiveInterpreter.write(data)
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.
127
Interactive Console Objects
128
---------------------------
130
The :class:`InteractiveConsole` class is a subclass of
131
:class:`InteractiveInterpreter`, and so offers all the methods of the
132
interpreter objects as well as the following additions.
135
.. method:: InteractiveConsole.interact([banner])
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!).
144
.. method:: InteractiveConsole.push(line)
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`).
156
.. method:: InteractiveConsole.resetbuffer()
158
Remove any unhandled source text from the input buffer.
161
.. method:: InteractiveConsole.raw_input([prompt])
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.