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 IPython
import sys

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 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
        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
        
        Result
        ------
        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:
            # Add line returns here, to make sure that the statement is
            # complete.
            return FrontEndBase.is_complete(self, string.rstrip() + '\n\n')


    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:
            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):
        """ Priflter 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)
        self.input_buffer = new_line
        if self.debug:
            print >>sys.__stdout__, completions 


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


    def write_completion(self, possibilities):
        """ Write the list of possible completions.
        """
        current_buffer = 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
        buf = []
        for symbol in possibilities:
            if pos < symbols_per_line:
                buf.append(symbol.ljust(max_len))
                pos += 1
            else:
                buf.append(symbol.rstrip() + '\n')
                pos = 1
        self.write(''.join(buf))
        self.new_prompt(self.input_prompt_template.substitute(
                            number=self.last_result['number'] + 1))
        self.input_buffer = current_buffer


    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)


    #--------------------------------------------------------------------------
    # Private API
    #--------------------------------------------------------------------------
 
    def _on_enter(self):
        """ Called when the return key is pressed in a line editing
            buffer.
        """
        current_buffer = self.input_buffer
        cleaned_buffer = self.prefilter_input(current_buffer)
        if self.is_complete(cleaned_buffer):
            self.execute(cleaned_buffer, raw_string=current_buffer)
        else:
            self.input_buffer += self._get_indent_string(
                                                current_buffer[:-1])
            if current_buffer[:-1].split('\n')[-1].rstrip().endswith(':'):
                self.input_buffer += '\t'


    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