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5.6 Python

The python module provides an interface which allows programmers to write loadable modules in Python. The syntax for loading the module is:

load-module name {
  command "python"
          " init-script=name"
          " load-path=path"
          " root-class=name";

All parameters are optional:

python module: load-path=path

Augments the default search path for Python modules. The format of path is the usual UNIX path specification: a colon-separated list of directory names.

python module: init-script=name

Specifies the name of the initial Python source file. This file will be loaded and interpreted immediately after loading the module.

python module: root-class=name

Sets the name of the Python root class, which is responsible for the dictionary operations.

A particular instance of the python module is loaded using the handler statement within a database block. This statement takes the same parameters as described above, plus any number of command line arguments, which will be passed to the root class constructor.

5.6.1 Python Dictionary Class

The dictionary class must define the following methods:

Method on DictionaryClass: __init__ self *argv

Class constructor. The argv array supplies positional arguments from the handler statement in the configuration file.

Method on DictionaryClass: open self dbname

Opens the database named dbname. Returns ‘True’ on success and ‘False’ on failure.

Method on DictionaryClass: close self

Closes the database.

Method on DictionaryClass: descr self

Returns a short description of the database.

Method on DictionaryClass: info self

Returns a text describing the database.

Method on DictionaryClass: lang self

Optional. Returns supported languages as ‘(src, dst)’.

Method on DictionaryClass: define_word self word

Defines word. Returns a result (an opaque Python object) if the definition was found or ‘False’ otherwise.

Method on DictionaryClass: match_word self strat word

Searches for word in the database using strategy strat. Returns a result (an opaque Python object) if some matches were found or ‘False’ otherwise.

Method on DictionaryClass: output self result n

Outputs nth result from the result set result.

Method on DictionaryClass: result_count self result

Returns number of elements in the result set.

Method on DictionaryClass: compare_count self result

Optional. Returns the number of comparisons performed when constructing the result set.

Method on DictionaryClass: result_headers self result hdr

Optional. Returns a dictionary of MIME headers.

Method on DictionaryClass: free_result self result

Reclaims any resources used by the result set.

5.6.2 Dico Python Primitives

Python primitive: register_strat name descr [proc]

Registers new match strategy. The arguments are:


Strategy name for use in the MATCH command.


The dscription, which will appear in the output of SHOW STRAT command.


Optional selector procedure.

If the proc argument is present, it must be the name of a Python function declared as:

def select(opcode key headword):

Its arguments are:


Integer operation code.


An DicoSelectionKey object identifying the search term (see DicoSelectionKey).


The headword being examined.

At the beginning of the search, the function is called with the ‘DICO_SELECT_BEGIN’ as its opcode argument. It must perform the necessary initialization and return.

At the end of the search loop, the function is called with opcodeDICO_SELECT_END’. It must perform the necessary deinitialization procedures and exit.

In both cases, the key and headword arguments are not defined.

Within the search loop, the function will be called for each headword from the database. The opcode parameter will be ‘DICO_SELECT_RUN’. In this case the function must return ‘True’ if the headword matches the key and ‘False’ otherwise.

Python primitive: register_markup name

Registers a markup name.

Python primitive: current_markup

Returns the name of the current markup. The DicoSelectionKey class

The DicoSelectionKey class represents a search key and is used when looking for matches. Calling str on the object of that class returns the search term itself, as does the word method:

Method on DicoSelectionKey: word

Returns the search term. It is equivalent to the __str__ attribute. The DicoStrategy class

A match strategy is represented by an object of the DicoStrategy class.

Variable of DicoStrategy: name

The name of that strategy.

Variable of DicoStrategy: descr

Textual description of the strategy.

Variable of DicoStrategy: has_selector

True’ if this strategy has a selector (see Python Selector).

Variable of DicoStrategy: name is_default

True’ if this is the default strategy.

Method on DicoStrategy: select headword key

Returns ‘True’ if key matches headword as per this strategy.

5.6.3 Python Example

In this subsection we will show a simple database module written in Python. This module handles simple textual databases in the following format:

Now, let’s create a module for handling this format. First, we need to import Dico primitives (see Dico Python Primitives) and the ‘sys’ module. The latter is needed for output functions:

import dico
import sys

Then, a result class will be needed for match_word and define_word methods. It will contain the actual data in the variable ‘result’:

class DicoResult:
    # actual data.
    result = {}
    # number of comparisons.
    compcount = 0
    def __init__ (self, *argv):
        self.result = argv[0]
        if len (argv) == 2:
             self.compcount = argv[1]

    def count (self):
        return len (self.result)

    def output (self, n):

    def append (self, elt):
        self.result.append (elt)

The following two classes extend ‘DicoResult’ for use with ‘DEFINE’ and ‘MATCH’ operations. The define_word method will return an instance of the ‘DicoDefineResult’ class:

class DicoDefineResult (DicoResult):
    def output (self, n):
        print "%d. %s" % (n + 1, self.result[n])
        print "---------",

The match_word method will return an instance of the ‘MatchResult’ class:

class DicoMatchResult (DicoResult):
    def output (self, n):
        sys.stdout.softspace = 0
        print self.result[n],

Now, let’s define the dictionary class:

class DicoModule:
    # The dictionary converted to associative array.
    adict =  {}
    # The database name.
    dbname = ''
    # The name of the corresponding disk file.
    filename = ''
    # A sort information about the database.
    mod_descr = ''
    # A verbose description of the database is kept.
    # as an array of strings.
    mod_info = []
    # A list of source and destination languages:
    langlist = ()

The class constructor takes a single argument, defining the name of the database file:

    def __init__ (self, *argv):
        self.filename = argv[0]

The ‘open’ method opens the database and reads its data:

    def open (self, dbname):
        self.dbname = dbname
        file = open (self.filename, "r")
        for line in file:
            if line.startswith ('--'):
            if line.startswith ('descr: '):
                self.mod_descr = line[7:].strip (' \n')
            if line.startswith ('info: '):
                self.mod_info.append (line[6:].strip (' \n'))
            if line.startswith ('lang: '):
                s = line[6:].strip (' \n').split(':', 2)
                if (len(s) == 1):
                    self.langlist = (s[0].split (), \
                                     s[0].split ())
                    self.langlist = (s[0].split (), \
                                     s[1].split ())
            f = line.strip (' \n').split (' ', 1)
            if len (f) == 2:
                self.adict[f[0].lower()] = f[1].strip (' ')
        return True

The database is kept entirely in memory, so there is no need for ‘close’ method. However, it must be declared anyway:

    def close (self):
        return True

The methods returning database information are trivial:

    def descr (self):
        return self.mod_descr

    def info (self):
        return '\n'.join (self.mod_info)
    def lang (self):
        return self.langlist

The ‘define_word’ method checks if the search term is present in the dictionary, and, if so, converts it to the DicoDefineResult:

    def define_word (self, word):
        if self.adict.has_key (word):
            return DicoDefineResult ([self.adict[word]])
        return False

The ‘match_word’ method supports the ‘exact’ strategy natively via the has_key attribute of adict:

    def match_word (self, strat, key):
        if == "exact":
            if self.adict.has_key (key.word.lower ()):
                return DicoMatchResult \

Other strategies are supported as long as they have selectors:

        elif strat.has_selector:
            res = DicoMatchResult ([], len (self.adict))
            for k in self.adict:
                if (k, key):
                    res.append (k)
            if res.count > 0:
                return res
        return False

The rest of methods rely on the result object to do the right thing:

    def output (self, rh, n):
        rh.output (n)
        return True

    def result_count (self, rh):
        return rh.count ()

    def compare_count (self, rh):
        return rh.compcount

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