"bicycle repair man"

README.MD

"Bicycle Repair Man" script showing a "zope-esque" prototype in less than 200 LoC using multiple inheritance and mixins.

This prototype was presented in Python Brasil 2011 in Sao Paulo, explaining at once a bit about what Zope does (did), and showng the capabilities of multiple inheritance.

(and likely not touched since).

Unfortunatelly I think the video for this lecture had not being made, or not survived - the other lectures in the same PyCon are here: https://www.youtube.com/watch?v=MDq4KecP3Bg&list=PLDC3uVLxaEQ3cPuehu65qU-QSNj6etm1q&ab_channel=pythonbrasil

bicycle.py

# -*- coding: utf-8 -*-
import wsgiref
from wsgiref.simple_server import make_server
from array import array
import itertools
import cPickle as pickle
import sys


mainfile = "data.fs"
MAXOBJ = 100
OFF_ITEM_SIZE = array("l").itemsize

"""

Persistence object file description:
a single file - the first OFF_ITEM_SIZE objects describe the offset where the 
root object is pickled too.

Each object is followed by MAXOBJ * OFF_ITEM_SIZE bytes, indicating the
offsets of contained objects in the file

"""

class Tree(object):
    """
    Basic mapping class supporting hierarchical structure
    and ordered contents.
    """
    folderish = True
    def __init__(self, name, parent):
        self.children = {}
        self.child_count = 0
        self.parent = parent
        self.name = name
        if parent is not None:
            self.parent[name] = self

    def __getitem__(self, name):
        return self.children[name]["obj"]
    def __setitem__(self, name, obj):
        if not name in self.children:
            self.children[name] = {}
            self.children[name]["order"] = self.child_count
            self.child_count += 1
        self.children[name]["obj"] = obj
        obj.name = name
    #TODO: Add  support to other methods on dictionary model later
    
    def get_url(self):
        path = "/" + self.name
        parent = self.parent
        while parent is not None:
            path = "/" + parent.name + path
            parent = parent.parent
        return path

class Traverse(Tree):
    """
    Implements traversal attribute search:
    retrieves attributes of higer elements on the
    on the tree structure if there is no child or 
    attribute with the required name
    """
    def __getattr__(self, attr):
        if attr in self.children:
            return self[attr]
        if self.parent is not None:
            return getattr(self.parent, attr)
        raise AttributeError ("%s does not exist" % attr)


class Persist(Tree):
    def __setitem__(self, name, obj):
        self.dirty = True
        return super(Persist, self).__setitem__(name, obj)
        
    def __getstate__(self):
        dct = self.__dict__.copy()
        dct["children"] = self.children.copy()
        for key  in dct["children"].keys():
            dct["children"][key] = dct["children"][key].copy()
            dct["children"][key]["obj"] = None
        dct["parent"] = None
        dct["dirty"] = False
        return dct
        
    def _save(self):
        # Move to end of file:
        data.seek(0, 2)
        self.offset = data.tell()
        pickle.dump(self, data, -1)
        self.contents_offset = data.tell()
        offset_data = []
        for name, obj in sorted(self.children.items(), key = lambda item: item[1]["order"]):
            offset_data.append(getattr("obj", "offset", -1))
        offset_data.extend(itertools.repeat(-1, MAXOBJ - len(self.children)))
        offset_data = array("l", offset_data)
        offset_data.tofile(data)
        #Update self position in parent's content index:
        if self.parent is not  None:
            index_in_parent = self.parent.children[self.name]["order"]
            position = self.parent.contents_offset + index_in_parent * OFF_ITEM_SIZE
        else:
            position = 0
        data.seek(position, 0)
        pos = array("l", [self.offset])
        pos.tofile(data)
        self.dirty = False
        
    def commit(self):
        if self.parent and hasattr(self.parent, "dirty") and self.parent.dirty:
            self.parent.commit()
        self._save()

    
    def __setstate__(self, state):
        #called by pickle on restoring -
        self.__dict__.update(state)
        stream_offset = data.tell()
        #walks over the end of pickle data. For protocol "2" it
        # is a single "." (chr(46)) byte
        data.seek(1,1)
        offsets = array("l")
        offsets.fromfile(data, MAXOBJ)
        for name, entry in self.children.items():
            entry["offset"] = offsets[entry["order"]]
        data.seek(stream_offset)

    def __getitem__(self, name):
        if name in self.children and self.children[name]["obj"] == None:
            # Load object from disk
            data.seek(self.children[name]["offset"], 0)
            self.children[name]["obj"] = pickle.load(data)
            self.children[name]["obj"].parent = self
        return super(Persist, self).__getitem__(name)
        

class Display(object):
    view_template = u"""<h1>%(title)s</h1>"""
    def view_repr(self, environ, start_response):
        start_response('200 OK', [('Content-type', 'text/html; charset=utf-8')])
        return [(self.view_template % self.todict()).encode("utf-8")]

    __call__ = view_repr

    def todict(self):
        dct = {}
        for attr_name in dir(self):
            if attr_name.startswith("_"):
                continue
            attribute =  getattr(self, attr_name)
            if isinstance(attribute, unicode):
                dct[attr_name] = attribute
        return dct
            
    def __repr__(self):
        return "Bicicle Repair Man Web Object"
    @property
    def title(self):
        return u"Bicicle Repair Man Web Object: %s" % self.name.decode("utf-8")
        
class BicicleRepairMan(Traverse, Persist, Display):
    pass

class Folder(BicicleRepairMan):
    view_template = u"""
    <h1>%(title)s</h1>
    <ul>
    %(children_list)s
    </ul>
    """
    @property
    def children_list(self):
        templ = u"""<li><a href="%s">%s</li>"""
        html = ""
        for name in self.children:
            html += templ %(self.get_url() + "/" + name, name)
        return html
    
    

def fetch_offset(file):
    data = array("l")
    data.fromfile(file,1)
    return data[0]
    
try:
    data = open("data.fs", "rb+")
    root_offset = fetch_offset(data)
    data.seek(root_offset)
    root = pickle.load(data)
except (IOError,EOFError) :
    data = open("data.fs", "wb+")
    array("l", [OFF_ITEM_SIZE]).tofile(data)
    root = BicicleRepairMan("root", None)
    root.commit()
    data.flush()

def dispatcher(environ, start_response):
    path_info = environ["PATH_INFO"].split("/")
    obj = root
    for name in path_info:
        if not name:
            continue
        try:
            obj = getattr(obj, name)
        except AttributeError:
            start_response('404 NOT FOUND', [('Content-type', 'text/html; charset=utf-8')])
            return (["<h1>404 NOT FOUND</h1>"])
    return obj(environ, start_response)


def init():
    r = root
    s = BicicleRepairMan("spawn", r)
    s2 = BicicleRepairMan("other", r)
    s3 = BicicleRepairMan("spawnned", s)
    s3.commit()
    s2.commit()
    s = Folder("folder", r)
    for x in range(5):
        s1 = Folder("child_%d" %x, s)
        s1.commit()
    for x in range(3):
        s2 = Folder("grandchild_%d" %x, s1)
        s2.commit()

    


if __name__ == "__main__":
    if len(sys.argv) == 2 and sys.argv[1] == "reset":
        init()
    server = make_server("127.0.0.1", 8000, dispatcher)
    server.serve_forever()