Doc/lib/libcode.tex

   1 \section{\module{code} ---
   2          Interpreter base classes}
   3 \declaremodule{standard}{code}
   4
   5 \modulesynopsis{Base classes for interactive Python interpreters.}
   6
   7
   8 The \code{code} module provides facilities to implement
   9 read-eval-print loops in Python.  Two classes and convenience
  10 functions are included which can be used to build applications which
  11 provide an interactive interpreter prompt.
  12
  13
  14 \begin{classdesc}{InteractiveInterpreter}{\optional{locals}}
  15 This class deals with parsing and interpreter state (the user's
  16 namespace); it does not deal with input buffering or prompting or
  17 input file naming (the filename is always passed in explicitly).
  18 The optional \var{locals} argument specifies the dictionary in
  19 which code will be executed; it defaults to a newly created
  20 dictionary with key \code{'__name__'} set to \code{'__console__'}
  21 and key \code{'__doc__'} set to \code{None}.
  22 \end{classdesc}
  23
  24 \begin{classdesc}{InteractiveConsole}{\optional{locals\optional{, filename}}}
  25 Closely emulate the behavior of the interactive Python interpreter.
  26 This class builds on \class{InteractiveInterpreter} and adds
  27 prompting using the familiar \code{sys.ps1} and \code{sys.ps2}, and
  28 input buffering.
  29 \end{classdesc}
  30
  31
  32 \begin{funcdesc}{interact}{\optional{banner\optional{,
  33                            readfunc\optional{, local}}}}
  34 Convenience function to run a read-eval-print loop.  This creates a
  35 new instance of \class{InteractiveConsole} and sets \var{readfunc}
  36 to be used as the \method{raw_input()} method, if provided.  If
  37 \var{local} is provided, it is passed to the
  38 \class{InteractiveConsole} constructor for use as the default
  39 namespace for the interpreter loop.  The \method{interact()} method
  40 of the instance is then run with \var{banner} passed as the banner
  41 to use, if provided.  The console object is discarded after use.
  42 \end{funcdesc}
  43
  44 \begin{funcdesc}{compile_command}{source\optional{,
  45                                   filename\optional{, symbol}}}
  46 This function is useful for programs that want to emulate Python's
  47 interpreter main loop (a.k.a. the read-eval-print loop).  The tricky
  48 part is to determine when the user has entered an incomplete command
  49 that can be completed by entering more text (as opposed to a
  50 complete command or a syntax error).  This function
  51 \emph{almost} always makes the same decision as the real interpreter
  52 main loop.
  53
  54 \var{source} is the source string; \var{filename} is the optional
  55 filename from which source was read, defaulting to \code{'<input>'};
  56 and \var{symbol} is the optional grammar start symbol, which should
  57 be either \code{'single'} (the default) or \code{'eval'}.
  58
  59 Returns a code object (the same as \code{compile(\var{source},
  60 \var{filename}, \var{symbol})}) if the command is complete and
  61 valid; \code{None} if the command is incomplete; raises
  62 \exception{SyntaxError} if the command is complete and contains a
  63 syntax error, or raises \exception{OverflowError} if the command
  64 includes a numeric constant which exceeds the range of the
  65 appropriate numeric type.
  66 \end{funcdesc}
  67
  68
  69 \subsection{Interactive Interpreter Objects
  70             \label{interpreter-objects}}
  71
  72 \begin{methoddesc}{runsource}{source\optional{, filename\optional{, symbol}}}
  73 Compile and run some source in the interpreter.
  74 Arguments are the same as for \function{compile_command()}; the
  75 default for \var{filename} is \code{'<input>'}, and for
  76 \var{symbol} is \code{'single'}.  One several things can happen:
  77
  78 \begin{itemize}
  79 \item
  80 The input is incorrect; \function{compile_command()} raised an
  81 exception (\exception{SyntaxError} or \exception{OverflowError}).  A
  82 syntax traceback will be printed by calling the
  83 \method{showsyntaxerror()} method.  \method{runsource()} returns
  84 \code{0}.
  85
  86 \item
  87 The input is incomplete, and more input is required;
  88 \function{compile_command()} returned \code{None}.
  89 \method{runsource()} returns \code{1}.
  90
  91 \item
  92 The input is complete; \function{compile_command()} returned a code
  93 object.  The code is executed by calling the \method{runcode()} (which
  94 also handles run-time exceptions, except for \exception{SystemExit}).
  95 \method{runsource()} returns \code{0}.
  96 \end{itemize}
  97
  98 The return value can be used to decide whether to use
  99 \code{sys.ps1} or \code{sys.ps2} to prompt the next line.
 100 \end{methoddesc}
 101
 102 \begin{methoddesc}{runcode}{code}
 103 Execute a code object.
 104 When an exception occurs, \method{showtraceback()} is called to
 105 display a traceback.  All exceptions are caught except
 106 \exception{SystemExit}, which is allowed to propagate.
 107
 108 A note about \exception{KeyboardInterrupt}: this exception may occur
 109 elsewhere in this code, and may not always be caught.  The caller
 110 should be prepared to deal with it.
 111 \end{methoddesc}
 112
 113 \begin{methoddesc}{showsyntaxerror}{\optional{filename}}
 114 Display the syntax error that just occurred.  This does not display
 115 a stack trace because there isn't one for syntax errors.
 116 If \var{filename} is given, it is stuffed into the exception instead
 117 of the default filename provided by Python's parser, because it
 118 always uses \code{'<string>'} when reading from a string.
 119 The output is written by the \method{write()} method.
 120 \end{methoddesc}
 121
 122 \begin{methoddesc}{showtraceback}{}
 123 Display the exception that just occurred.  We remove the first stack
 124 item because it is within the interpreter object implementation.
 125 The output is written by the \method{write()} method.
 126 \end{methoddesc}
 127
 128 \begin{methoddesc}{write}{data}
 129 Write a string to the standard error stream (\code{sys.stderr}).
 130 Derived classes should override this to provide the appropriate output
 131 handling as needed.
 132 \end{methoddesc}
 133
 134
 135 \subsection{Interactive Console Objects
 136             \label{console-objects}}
 137
 138 The \class{InteractiveConsole} class is a subclass of
 139 \class{InteractiveInterpreter}, and so offers all the methods of the
 140 interpreter objects as well as the following additions.
 141
 142 \begin{methoddesc}{interact}{\optional{banner}}
 143 Closely emulate the interactive Python console.
 144 The optional banner argument specify the banner to print before the
 145 first interaction; by default it prints a banner similar to the one
 146 printed by the standard Python interpreter, followed by the class
 147 name of the console object in parentheses (so as not to confuse this
 148 with the real interpreter -- since it's so close!).
 149 \end{methoddesc}
 150
 151 \begin{methoddesc}{push}{line}
 152 Push a line of source text to the interpreter.
 153 The line should not have a trailing newline; it may have internal
 154 newlines.  The line is appended to a buffer and the interpreter's
 155 \method{runsource()} method is called with the concatenated contents
 156 of the buffer as source.  If this indicates that the command was
 157 executed or invalid, the buffer is reset; otherwise, the command is
 158 incomplete, and the buffer is left as it was after the line was
 159 appended.  The return value is \code{1} if more input is required,
 160 \code{0} if the line was dealt with in some way (this is the same as
 161 \method{runsource()}).
 162 \end{methoddesc}
 163
 164 \begin{methoddesc}{resetbuffer}{}
 165 Remove any unhandled source text from the input buffer.
 166 \end{methoddesc}
 167
 168 \begin{methoddesc}{raw_input}{\optional{prompt}}
 169 Write a prompt and read a line.  The returned line does not include
 170 the trailing newline.  When the user enters the \EOF{} key sequence,
 171 \exception{EOFError} is raised.  The base implementation uses the
 172 built-in function \function{raw_input()}; a subclass may replace this
 173 with a different implementation.
 174 \end{methoddesc}