IPython/frontend/linefrontendbase.py

"""
Base front end class for all line-oriented frontends, rather than
block-oriented.

Currently this focuses on synchronous frontends.
"""
__docformat__ = "restructuredtext en"

#-------------------------------------------------------------------------------
#  Copyright (C) 2008  The IPython Development Team
#
#  Distributed under the terms of the BSD License.  The full license is in
#  the file COPYING, distributed as part of this software.
#-------------------------------------------------------------------------------

#-------------------------------------------------------------------------------
# Imports
#-------------------------------------------------------------------------------
import re

import sys
import codeop

from frontendbase import FrontEndBase
from IPython.kernel.core.interpreter import Interpreter

def common_prefix(strings):
    """ Given a list of strings, return the common prefix between all
        these strings.
    """
    ref = strings[0]
    prefix = ''
    for size in range(len(ref)):
        test_prefix = ref[:size+1]
        for string in strings[1:]:
            if not string.startswith(test_prefix):
                return prefix
        prefix = test_prefix

    return prefix

#-----------------------------------------------------------------------------
# Base class for the line-oriented front ends
#-----------------------------------------------------------------------------

class LineFrontEndBase(FrontEndBase):
    """ Concrete implementation of the FrontEndBase class. This is meant
    to be the base class behind all the frontend that are line-oriented,
    rather than block-oriented.
    """
    
    # We need to keep the prompt number, to be able to increment
    # it when there is an exception.
    prompt_number = 1

    # We keep a reference to the last result: it helps testing and
    # programatic control of the frontend. 
    last_result = dict(number=0)

    # The last prompt displayed. Useful for continuation prompts.
    last_prompt = ''

    # The input buffer being edited
    input_buffer = ''

    # Set to true for debug output
    debug = False

    # A banner to print at startup
    banner = None

    #--------------------------------------------------------------------------
    # FrontEndBase interface
    #--------------------------------------------------------------------------

    def __init__(self, shell=None, history=None, banner=None, *args, **kwargs):
        if shell is None:
            shell = Interpreter()
        FrontEndBase.__init__(self, shell=shell, history=history)

        if banner is not None:
            self.banner = banner

    def start(self):
        """ Put the frontend in a state where it is ready for user
            interaction.
        """
        if self.banner is not None:
            self.write(self.banner, refresh=False)

        self.new_prompt(self.input_prompt_template.substitute(number=1))


    def complete(self, line):
        """Complete line in engine's user_ns
        
        Parameters
        ----------
        line : string
        
        Returns
        -------
        The replacement for the line and the list of possible completions.
        """
        completions = self.shell.complete(line)
        complete_sep =  re.compile('[\s\{\}\[\]\(\)\=]')
        if completions:
            prefix = common_prefix(completions) 
            residual = complete_sep.split(line)[:-1]
            line = line[:-len(residual)] + prefix
        return line, completions 
 

    def render_result(self, result):
        """ Frontend-specific rendering of the result of a calculation
        that has been sent to an engine.
        """
        if 'stdout' in result and result['stdout']:
            self.write('\n' + result['stdout'])
        if 'display' in result and result['display']:
            self.write("%s%s\n" % ( 
                            self.output_prompt_template.substitute(
                                    number=result['number']),
                            result['display']['pprint']
                            ) )
       

    def render_error(self, failure):
        """ Frontend-specific rendering of error. 
        """
        self.write('\n\n'+str(failure)+'\n\n')
        return failure


    def is_complete(self, string):
        """ Check if a string forms a complete, executable set of
        commands.

        For the line-oriented frontend, multi-line code is not executed
        as soon as it is complete: the users has to enter two line
        returns.
        """
        if string in ('', '\n'):
            # Prefiltering, eg through ipython0, may return an empty
            # string although some operations have been accomplished. We
            # thus want to consider an empty string as a complete
            # statement.
            return True
        elif ( len(self.input_buffer.split('\n'))>2 
                        and not re.findall(r"\n[\t ]*\n[\t ]*$", string)):
            return False
        else:
            self.capture_output()
            try:
                # Add line returns here, to make sure that the statement is
                # complete (except if '\' was used).
                # This should probably be done in a different place (like
                # maybe 'prefilter_input' method? For now, this works.
                clean_string = string.rstrip('\n')
                if not clean_string.endswith('\\'): clean_string +='\n\n' 
                is_complete = codeop.compile_command(clean_string,
                            "<string>", "exec")
                self.release_output()
            except Exception, e:
                # XXX: Hack: return True so that the
                # code gets executed and the error captured.
                is_complete = True
            return is_complete


    def write(self, string, refresh=True):
        """ Write some characters to the display.

            Subclass should overide this method.

            The refresh keyword argument is used in frontends with an
            event loop, to choose whether the write should trigget an UI
            refresh, and thus be syncrhonous, or not.
        """
        print >>sys.__stderr__, string


    def execute(self, python_string, raw_string=None):
        """ Stores the raw_string in the history, and sends the
        python string to the interpreter.
        """
        if raw_string is None:
            raw_string = python_string
        # Create a false result, in case there is an exception
        self.last_result = dict(number=self.prompt_number)

        try:
            try:
                self.history.input_cache[-1] = raw_string.rstrip()
                result = self.shell.execute(python_string)
                self.last_result = result
                self.render_result(result)
            except:
                self.show_traceback()
        finally:
            self.after_execute()


    #--------------------------------------------------------------------------
    # LineFrontEndBase interface
    #--------------------------------------------------------------------------

    def prefilter_input(self, string):
        """ Prefilter the input to turn it in valid python.
        """
        string = string.replace('\r\n', '\n')
        string = string.replace('\t', 4*' ')
        # Clean the trailing whitespace
        string = '\n'.join(l.rstrip()  for l in string.split('\n'))
        return string


    def after_execute(self):
        """ All the operations required after an execution to put the
            terminal back in a shape where it is usable.
        """
        self.prompt_number += 1
        self.new_prompt(self.input_prompt_template.substitute(
                            number=(self.last_result['number'] + 1)))
        # Start a new empty history entry
        self._add_history(None, '')
        self.history_cursor = len(self.history.input_cache) - 1


    def complete_current_input(self):
        """ Do code completion on current line. 
        """
        if self.debug:
            print >>sys.__stdout__, "complete_current_input", 
        line = self.input_buffer
        new_line, completions = self.complete(line)
        if len(completions)>1:
            self.write_completion(completions, new_line=new_line)
        elif not line == new_line:
            self.input_buffer = new_line
        if self.debug:
            print >>sys.__stdout__, 'line', line
            print >>sys.__stdout__, 'new_line', new_line
            print >>sys.__stdout__, completions 


    def get_line_width(self):
        """ Return the width of the line in characters.
        """
        return 80


    def write_completion(self, possibilities, new_line=None):
        """ Write the list of possible completions.

            new_line is the completed input line that should be displayed
            after the completion are writen. If None, the input_buffer
            before the completion is used.
        """
        if new_line is None:
            new_line = self.input_buffer
        
        self.write('\n')
        max_len = len(max(possibilities, key=len)) + 1
        
        # Now we check how much symbol we can put on a line...
        chars_per_line = self.get_line_width()
        symbols_per_line = max(1, chars_per_line/max_len)

        pos = 1
        completion_string = []
        for symbol in possibilities:
            if pos < symbols_per_line:
                completion_string.append(symbol.ljust(max_len))
                pos += 1
            else:
                completion_string.append(symbol.rstrip() + '\n')
                pos = 1
        self.write(''.join(completion_string))
        self.new_prompt(self.input_prompt_template.substitute(
                            number=self.last_result['number'] + 1))
        self.input_buffer = new_line


    def new_prompt(self, prompt):
        """ Prints a prompt and starts a new editing buffer. 

            Subclasses should use this method to make sure that the
            terminal is put in a state favorable for a new line
            input.
        """
        self.input_buffer = ''
        self.write(prompt)


    def continuation_prompt(self):
        """Returns the current continuation prompt.
        """
        return ("."*(len(self.last_prompt)-2) + ': ')
 

    def execute_command(self, command, hidden=False):
        """ Execute a command, not only in the model, but also in the
            view, if any.
        """
        return self.shell.execute(command)

    #--------------------------------------------------------------------------
    # Private API
    #--------------------------------------------------------------------------
 
    def _on_enter(self, new_line_pos=0):
        """ Called when the return key is pressed in a line editing
            buffer.

            Parameters
            ----------
            new_line_pos : integer, optional
                Position of the new line to add, starting from the
                end (0 adds a new line after the last line, -1 before
                the last line...)

            Returns
            -------
            True if execution is triggered
        """
        current_buffer = self.input_buffer
        # XXX: This string replace is ugly, but there should be no way it
        # fails.
        prompt_less_buffer = re.sub('^' + self.continuation_prompt(),
                '', current_buffer).replace('\n' + self.continuation_prompt(),
                                            '\n')
        cleaned_buffer = self.prefilter_input(prompt_less_buffer)
        if self.is_complete(cleaned_buffer):
            self.execute(cleaned_buffer, raw_string=current_buffer)
            return True
        else:
            # Start a new line.
            new_line_pos = -new_line_pos
            lines = current_buffer.split('\n')[:-1]
            prompt_less_lines = prompt_less_buffer.split('\n')
            # Create the new line, with the continuation prompt, and the 
            # same amount of indent than the line above it.
            new_line = self.continuation_prompt() + \
                  self._get_indent_string('\n'.join(
                                    prompt_less_lines[:new_line_pos-1]))
            if len(lines) == 1:
                # We are starting a first continuation line. Indent it.
                new_line += '\t'
            elif current_buffer[:-1].split('\n')[-1].rstrip().endswith(':'):
                # The last line ends with ":", autoindent the new line.
                new_line += '\t'

            if new_line_pos == 0:
                lines.append(new_line)
            else:
                lines.insert(new_line_pos, new_line)
            self.input_buffer = '\n'.join(lines)
            

    def _get_indent_string(self, string):
        """ Return the string of whitespace that prefixes a line. Used to
        add the right amount of indendation when creating a new line.
        """
        string = string.replace('\t', ' '*4)
        string = string.split('\n')[-1]
        indent_chars = len(string) - len(string.lstrip())
        indent_string = '\t'*(indent_chars // 4) + \
                            ' '*(indent_chars % 4)

        return indent_string