pan_file.py

import os
import sys
import re

class pan_exception(Exception):
    '''Exception to be risen by a header processor, to indicate
    something goes wrong with it'''
    pass

class pan_file(object):
    '''Pan file to be automatically regenerated'''
    tpl_name_re = re.compile('^\w*\s*template\s+([-\w]+)\s*;$')
    act_re = re.compile('^@{\s*(\S+?)\s*=\s*(.*)}$')
    def __init__(self, filename, **actions):
        '''Class constructor. Takes the name of the Pan file to open,
        and the a dictionary with the actions registered to each
        possible header.'''
        self.file = open(filename, "r+")
        self.actions = actions
        self.body = []
        self.open = True

    def __iter__(self):
        '''The object iterates over its header.'''
        self.file.seek(0,0)
        self.open = True
        return self

    def next(self):
        if not self.open:
            raise StopIteration
        i = self.file.readline()
        while i:
            m = self.act_re.match(i)
            if m:
                return (m.group(1), m.group(2))
            m = self.tpl_name_re.match(i)
            if m:
                break
            i = self.file.readline()
        self.open = False
        raise StopIteration

    def process(self):
        '''Processes the header of a Pan file, performing any
        registered actions'''
        self.body = []
        for action, args in self:
            try:
                f = self.actions[action]
                v = f(args)
                if type(v) is str:
                    self.body.append(v)
                else:
                    self.body.extend(v)
            except KeyError, e:
                pass

    def write_file(self):
        '''Writes to the file, if it's needed.

        If the old contents and the new ones are the same, the old
        file is kept, to avoid useless recompilations. Also, if the
        new body is empty, which most likely means the documentation
        strings were not meant to be consumed by us, the file is kept.
        
        Otherwise, it assumes all contents should be generated by this
        processor, and destroys any previous content.'''
        if not self.body:
            return False
        pos = self.file.tell()
        new = '\n'.join(self.body)
        old = ''.join(self.file)
        if new == old:
            return False
        self.file.seek(pos, 0)
        self.file.truncate()
        self.file.write(new)
        self.file.close()
        return True

def wrap_in_variable(name):
    '''Decorator function, for wrapping the return value of a function
into a Pan variable'''
    rx = re.compile('\W+')
    variable = rx.sub('_', name).upper()
    def wrap(f):
        def code_to_pan_variable(*args, **kwargs):
            st = 'variable ' + variable + ' ?= '
            rt = f(*args, **kwargs)

            if rt.__class__ is list:
                st +='list(\n' + ',\n'.join(["    '%s'" % (str(x)) for x in rt])
                st += ');\n'
            elif rt.__class__ is dict:
                st += 'nlist(\n'
                st += ',\n'.join(["    '%s', '%s'" % (k, str(v)) for k, v in rt.iteritems()])
                st += ');\n'
            else:
                st += "'%s'" % rt
                st += ';\n'
            return st
        return code_to_pan_variable
    return wrap