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code.py
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"""Utilities needed to emulate Python's interactive interpreter. """ # Inspired by similar code by Jeff Epler and Fredrik Lundh. import sys import traceback from codeop import CommandCompiler, compile_command __all__ = ["InteractiveInterpreter", "InteractiveConsole", "interact", "compile_command"] def softspace(file, newvalue): oldvalue = 0 try: oldvalue = file.softspace except AttributeError: pass try: file.softspace = newvalue except (AttributeError, TypeError): # "attribute-less object" or "read-only attributes" pass return oldvalue class InteractiveInterpreter: """Base class for InteractiveConsole. This class deals with parsing and interpreter state (the user's namespace); it doesn't deal with input buffering or prompting or input file naming (the filename is always passed in explicitly). """ def __init__(self, locals=None): """Constructor. The optional 'locals' argument specifies the dictionary in which code will be executed; it defaults to a newly created dictionary with key "__name__" set to "__console__" and key "__doc__" set to None. """ if locals is None: locals = {"__name__": "__console__", "__doc__": None} self.locals = locals self.compile = CommandCompiler() def runsource(self, source, filename="<input>", symbol="single"): """Compile and run some source in the interpreter. Arguments are as for compile_command(). One several things can happen: 1) The input is incorrect; compile_command() raised an exception (SyntaxError or OverflowError). A syntax traceback will be printed by calling the showsyntaxerror() method. 2) The input is incomplete, and more input is required; compile_command() returned None. Nothing happens. 3) The input is complete; compile_command() returned a code object. The code is executed by calling self.runcode() (which also handles run-time exceptions, except for SystemExit). The return value is True in case 2, False in the other cases (unless an exception is raised). The return value can be used to decide whether to use sys.ps1 or sys.ps2 to prompt the next line. """ try: code = self.compile(source, filename, symbol) except (OverflowError, SyntaxError, ValueError): # Case 1 self.showsyntaxerror(filename) return False if code is None: # Case 2 return True # Case 3 self.runcode(code) return False def runcode(self, code): """Execute a code object. When an exception occurs, self.showtraceback() is called to display a traceback. All exceptions are caught except SystemExit, which is reraised. A note about KeyboardInterrupt: this exception may occur elsewhere in this code, and may not always be caught. The caller should be prepared to deal with it. """ try: exec code in self.locals except SystemExit: raise except: self.showtraceback() else: if softspace(sys.stdout, 0): print def showsyntaxerror(self, filename=None): """Display the syntax error that just occurred. This doesn't display a stack trace because there isn't one. If a filename is given, it is stuffed in the exception instead of what was there before (because Python's parser always uses "<string>" when reading from a string). The output is written by self.write(), below. """ type, value, sys.last_traceback = sys.exc_info() sys.last_type = type sys.last_value = value if filename and type is SyntaxError: # Work hard to stuff the correct filename in the exception try: msg, (dummy_filename, lineno, offset, line) = value except: # Not the format we expect; leave it alone pass else: # Stuff in the right filename value = SyntaxError(msg, (filename, lineno, offset, line)) sys.last_value = value list = traceback.format_exception_only(type, value) map(self.write, list) def showtraceback(self): """Display the exception that just occurred. We remove the first stack item because it is our own code. The output is written by self.write(), below. """ try: type, value, tb = sys.exc_info() sys.last_type = type sys.last_value = value sys.last_traceback = tb tblist = traceback.extract_tb(tb) del tblist[:1] list = traceback.format_list(tblist) if list: list.insert(0, "Traceback (most recent call last):\n") list[len(list):] = traceback.format_exception_only(type, value) finally: tblist = tb = None map(self.write, list) def write(self, data): """Write a string. The base implementation writes to sys.stderr; a subclass may replace this with a different implementation. """ sys.stderr.write(data) class InteractiveConsole(InteractiveInterpreter): """Closely emulate the behavior of the interactive Python interpreter. This class builds on InteractiveInterpreter and adds prompting using the familiar sys.ps1 and sys.ps2, and input buffering. """ def __init__(self, locals=None, filename="<console>"): """Constructor. The optional locals argument will be passed to the InteractiveInterpreter base class. The optional filename argument should specify the (file)name of the input stream; it will show up in tracebacks. """ InteractiveInterpreter.__init__(self, locals) self.filename = filename self.resetbuffer() def resetbuffer(self): """Reset the input buffer.""" self.buffer = [] def interact(self, banner=None): """Closely emulate the interactive Python console. The optional banner argument specify the banner to print before the first interaction; by default it prints a banner similar to the one printed by the real Python interpreter, followed by the current class name in parentheses (so as not to confuse this with the real interpreter -- since it's so close!). """ try: sys.ps1 except AttributeError: sys.ps1 = ">>> " try: sys.ps2 except AttributeError: sys.ps2 = "... " cprt = 'Type "help", "copyright", "credits" or "license" for more information.' if banner is None: self.write("Python %s on %s\n%s\n(%s)\n" % (sys.version, sys.platform, cprt, self.__class__.__name__)) else: self.write("%s\n" % str(banner)) more = 0 while 1: try: if more: prompt = sys.ps2 else: prompt = sys.ps1 try: line = self.raw_input(prompt) # Can be None if sys.stdin was redefined encoding = getattr(sys.stdin, "encoding", None) if encoding and not isinstance(line, unicode): line = line.decode(encoding) except EOFError: self.write("\n") break else: more = self.push(line) except KeyboardInterrupt: self.write("\nKeyboardInterrupt\n") self.resetbuffer() more = 0 def push(self, line): """Push a line to the interpreter. The line should not have a trailing newline; it may have internal newlines. The line is appended to a buffer and the interpreter's runsource() method is called with the concatenated contents of the buffer as source. If this indicates that the command was executed or invalid, the buffer is reset; otherwise, the command is incomplete, and the buffer is left as it was after the line was appended. The return value is 1 if more input is required, 0 if the line was dealt with in some way (this is the same as runsource()). """ self.buffer.append(line) source = "\n".join(self.buffer) more = self.runsource(source, self.filename) if not more: self.resetbuffer() return more def raw_input(self, prompt=""): """Write a prompt and read a line. The returned line does not include the trailing newline. When the user enters the EOF key sequence, EOFError is raised. The base implementation uses the built-in function raw_input(); a subclass may replace this with a different implementation. """ return raw_input(prompt) def interact(banner=None, readfunc=None, local=None): """Closely emulate the interactive Python interpreter. This is a backwards compatible interface to the InteractiveConsole class. When readfunc is not specified, it attempts to import the readline module to enable GNU readline if it is available. Arguments (all optional, all default to None): banner -- passed to InteractiveConsole.interact() readfunc -- if not None, replaces InteractiveConsole.raw_input() local -- passed to InteractiveInterpreter.__init__() """ console = InteractiveConsole(local) if readfunc is not None: console.raw_input = readfunc else: try: import readline except ImportError: pass console.interact(banner) if __name__ == "__main__": interact()