Lib/code.py

   1 """Utilities needed to emulate Python's interactive interpreter.
   2
   3 """
   4
   5 # Inspired by similar code by Jeff Epler and Fredrik Lundh.
   6
   7
   8 import sys
   9 import traceback
  10 from codeop import CommandCompiler, compile_command
  11
  12 __all__ = ["InteractiveInterpreter", "InteractiveConsole", "interact",
  13            "compile_command"]
  14
  15 def softspace(file, newvalue):
  16     oldvalue = 0
  17     try:
  18         oldvalue = file.softspace
  19     except AttributeError:
  20         pass
  21     try:
  22         file.softspace = newvalue
  23     except (AttributeError, TypeError):
  24         # "attribute-less object" or "read-only attributes"
  25         pass
  26     return oldvalue
  27
  28 class InteractiveInterpreter:
  29     """Base class for InteractiveConsole.
  30
  31     This class deals with parsing and interpreter state (the user's
  32     namespace); it doesn't deal with input buffering or prompting or
  33     input file naming (the filename is always passed in explicitly).
  34
  35     """
  36
  37     def __init__(self, locals=None):
  38         """Constructor.
  39
  40         The optional 'locals' argument specifies the dictionary in
  41         which code will be executed; it defaults to a newly created
  42         dictionary with key "__name__" set to "__console__" and key
  43         "__doc__" set to None.
  44
  45         """
  46         if locals is None:
  47             locals = {"__name__": "__console__", "__doc__": None}
  48         self.locals = locals
  49         self.compile = CommandCompiler()
  50
  51     def runsource(self, source, filename="<input>", symbol="single"):
  52         """Compile and run some source in the interpreter.
  53
  54         Arguments are as for compile_command().
  55
  56         One several things can happen:
  57
  58         1) The input is incorrect; compile_command() raised an
  59         exception (SyntaxError or OverflowError).  A syntax traceback
  60         will be printed by calling the showsyntaxerror() method.
  61
  62         2) The input is incomplete, and more input is required;
  63         compile_command() returned None.  Nothing happens.
  64
  65         3) The input is complete; compile_command() returned a code
  66         object.  The code is executed by calling self.runcode() (which
  67         also handles run-time exceptions, except for SystemExit).
  68
  69         The return value is True in case 2, False in the other cases (unless
  70         an exception is raised).  The return value can be used to
  71         decide whether to use sys.ps1 or sys.ps2 to prompt the next
  72         line.
  73
  74         """
  75         try:
  76             code = self.compile(source, filename, symbol)
  77         except (OverflowError, SyntaxError, ValueError):
  78             # Case 1
  79             self.showsyntaxerror(filename)
  80             return False
  81
  82         if code is None:
  83             # Case 2
  84             return True
  85
  86         # Case 3
  87         self.runcode(code)
  88         return False
  89
  90     def runcode(self, code):
  91         """Execute a code object.
  92
  93         When an exception occurs, self.showtraceback() is called to
  94         display a traceback.  All exceptions are caught except
  95         SystemExit, which is reraised.
  96
  97         A note about KeyboardInterrupt: this exception may occur
  98         elsewhere in this code, and may not always be caught.  The
  99         caller should be prepared to deal with it.
 100
 101         """
 102         try:
 103             exec code in self.locals
 104         except SystemExit:
 105             raise
 106         except:
 107             self.showtraceback()
 108         else:
 109             if softspace(sys.stdout, 0):
 110                 print
 111
 112     def showsyntaxerror(self, filename=None):
 113         """Display the syntax error that just occurred.
 114
 115         This doesn't display a stack trace because there isn't one.
 116
 117         If a filename is given, it is stuffed in the exception instead
 118         of what was there before (because Python's parser always uses
 119         "<string>" when reading from a string).
 120
 121         The output is written by self.write(), below.
 122
 123         """
 124         type, value, sys.last_traceback = sys.exc_info()
 125         sys.last_type = type
 126         sys.last_value = value
 127         if filename and type is SyntaxError:
 128             # Work hard to stuff the correct filename in the exception
 129             try:
 130                 msg, (dummy_filename, lineno, offset, line) = value
 131             except:
 132                 # Not the format we expect; leave it alone
 133                 pass
 134             else:
 135                 # Stuff in the right filename
 136                 value = SyntaxError(msg, (filename, lineno, offset, line))
 137                 sys.last_value = value
 138         list = traceback.format_exception_only(type, value)
 139         map(self.write, list)
 140
 141     def showtraceback(self):
 142         """Display the exception that just occurred.
 143
 144         We remove the first stack item because it is our own code.
 145
 146         The output is written by self.write(), below.
 147
 148         """
 149         try:
 150             type, value, tb = sys.exc_info()
 151             sys.last_type = type
 152             sys.last_value = value
 153             sys.last_traceback = tb
 154             tblist = traceback.extract_tb(tb)
 155             del tblist[:1]
 156             list = traceback.format_list(tblist)
 157             if list:
 158                 list.insert(0, "Traceback (most recent call last):\n")
 159             list[len(list):] = traceback.format_exception_only(type, value)
 160         finally:
 161             tblist = tb = None
 162         map(self.write, list)
 163
 164     def write(self, data):
 165         """Write a string.
 166
 167         The base implementation writes to sys.stderr; a subclass may
 168         replace this with a different implementation.
 169
 170         """
 171         sys.stderr.write(data)
 172
 173
 174 class InteractiveConsole(InteractiveInterpreter):
 175     """Closely emulate the behavior of the interactive Python interpreter.
 176
 177     This class builds on InteractiveInterpreter and adds prompting
 178     using the familiar sys.ps1 and sys.ps2, and input buffering.
 179
 180     """
 181
 182     def __init__(self, locals=None, filename="<console>"):
 183         """Constructor.
 184
 185         The optional locals argument will be passed to the
 186         InteractiveInterpreter base class.
 187
 188         The optional filename argument should specify the (file)name
 189         of the input stream; it will show up in tracebacks.
 190
 191         """
 192         InteractiveInterpreter.__init__(self, locals)
 193         self.filename = filename
 194         self.resetbuffer()
 195
 196     def resetbuffer(self):
 197         """Reset the input buffer."""
 198         self.buffer = []
 199
 200     def interact(self, banner=None):
 201         """Closely emulate the interactive Python console.
 202
 203         The optional banner argument specify the banner to print
 204         before the first interaction; by default it prints a banner
 205         similar to the one printed by the real Python interpreter,
 206         followed by the current class name in parentheses (so as not
 207         to confuse this with the real interpreter -- since it's so
 208         close!).
 209
 210         """
 211         try:
 212             sys.ps1
 213         except AttributeError:
 214             sys.ps1 = ">>> "
 215         try:
 216             sys.ps2
 217         except AttributeError:
 218             sys.ps2 = "... "
 219         cprt = 'Type "help", "copyright", "credits" or "license" for more information.'
 220         if banner is None:
 221             self.write("Python %s on %s\n%s\n(%s)\n" %
 222                        (sys.version, sys.platform, cprt,
 223                         self.__class__.__name__))
 224         else:
 225             self.write("%s\n" % str(banner))
 226         more = 0
 227         while 1:
 228             try:
 229                 if more:
 230                     prompt = sys.ps2
 231                 else:
 232                     prompt = sys.ps1
 233                 try:
 234                     line = self.raw_input(prompt)
 235                     # Can be None if sys.stdin was redefined
 236                     encoding = getattr(sys.stdin, "encoding", None)
 237                     if encoding and not isinstance(line, unicode):
 238                         line = line.decode(encoding)
 239                 except EOFError:
 240                     self.write("\n")
 241                     break
 242                 else:
 243                     more = self.push(line)
 244             except KeyboardInterrupt:
 245                 self.write("\nKeyboardInterrupt\n")
 246                 self.resetbuffer()
 247                 more = 0
 248
 249     def push(self, line):
 250         """Push a line to the interpreter.
 251
 252         The line should not have a trailing newline; it may have
 253         internal newlines.  The line is appended to a buffer and the
 254         interpreter's runsource() method is called with the
 255         concatenated contents of the buffer as source.  If this
 256         indicates that the command was executed or invalid, the buffer
 257         is reset; otherwise, the command is incomplete, and the buffer
 258         is left as it was after the line was appended.  The return
 259         value is 1 if more input is required, 0 if the line was dealt
 260         with in some way (this is the same as runsource()).
 261
 262         """
 263         self.buffer.append(line)
 264         source = "\n".join(self.buffer)
 265         more = self.runsource(source, self.filename)
 266         if not more:
 267             self.resetbuffer()
 268         return more
 269
 270     def raw_input(self, prompt=""):
 271         """Write a prompt and read a line.
 272
 273         The returned line does not include the trailing newline.
 274         When the user enters the EOF key sequence, EOFError is raised.
 275
 276         The base implementation uses the built-in function
 277         raw_input(); a subclass may replace this with a different
 278         implementation.
 279
 280         """
 281         return raw_input(prompt)
 282
 283
 284 def interact(banner=None, readfunc=None, local=None):
 285     """Closely emulate the interactive Python interpreter.
 286
 287     This is a backwards compatible interface to the InteractiveConsole
 288     class.  When readfunc is not specified, it attempts to import the
 289     readline module to enable GNU readline if it is available.
 290
 291     Arguments (all optional, all default to None):
 292
 293     banner -- passed to InteractiveConsole.interact()
 294     readfunc -- if not None, replaces InteractiveConsole.raw_input()
 295     local -- passed to InteractiveInterpreter.__init__()
 296
 297     """
 298     console = InteractiveConsole(local)
 299     if readfunc is not None:
 300         console.raw_input = readfunc
 301     else:
 302         try:
 303             import readline
 304         except ImportError:
 305             pass
 306     console.interact(banner)
 307
 308
 309 if __name__ == "__main__":
 310     interact()