Flattened nested dict, all items are settable and gettable through ['item1']['item2'] standard form or ['item1/item2'] internal form. This allows to replace the internal dict with any on-disk storage system like a shelve's shelf (great for huge nested dicts that cannot fit into memory). Main limitation: an entry can be both a singleton and a nes…

flattened_nested_dict.py

#!/usr/bin/env python
#
# Flattened nested dict
# Copyright (C) 2017 Larroque Stephen
#
# Licensed under the MIT License (MIT)
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
#

import shelve
import sys

PY3 = (sys.version_info >= (3,0))

class fdict(dict):
    '''Flattened nested dict, all items are settable and gettable through ['item1']['item2'] standard form or ['item1/item2'] internal form.
    This allows to replace the internal dict with any on-disk storage system like a shelve's shelf (great for huge nested dicts that cannot fit into memory).
    Main limitation: an entry can be both a singleton and a nested fdict, and there is no way to tell what is what, no error will be shown, the singleton will always be returned.
    '''
    def __init__(self, d=None, rootpath='', delimiter='/', *args):
        if d:
            self.d = d
        else:
            self.d = {}
        self.rootpath = rootpath
        self.delimiter = delimiter
        self._py3compat()
        #return dict.__init__(self, *args)

    def _py3compat(self):
        if PY3:
            # Py3
            self._viewkeys = self.d.keys
            self._viewvalues = self.d.values
            self._viewitems = self.d.items
        else:
            # Py2
            if getattr(self.d, "viewvalues", None):
                # Py2.7
                self._viewkeys = self.d.viewkeys
                self._viewvalues = self.d.viewvalues
                self._viewitems = self.d.viewitems
            else:
                # Py2.6
                self._viewkeys = self.d.iterkeys
                self._viewvalues = self.d.itervalues
                self._viewitems = self.d.iteritems

    def _buildpath(self, key):
        return self.rootpath+self.delimiter+key if self.rootpath else key

    def __getitem__(self, key):
        # Node or leaf?
        if key in self.d: # Leaf: return the value
            return self.d.__getitem__(key)
        else: # Node: return a new full fdict based on the old one but with a different rootpath to limit the results by default
            return fdict(d=self.d, rootpath=self._buildpath(key))
        #return dict.__getitem__(self, key)

    def __setitem__(self, key, value):
        #fullkey = self._buildpath(key)
        #if fullkey in self.d and :
        #    raise ValueError('Conflict detected: the following key is both a singleton and a nested dict: %s' % fullkey)
        self.d.__setitem__(self._buildpath(key), value)
        #dict.__setitem__(self, key, value)

    #def addchild(self, key, value=None):
    #    self.d[self._buildpath(key)] = value

    def viewkeys(self):
        if not self.rootpath:
            return self._viewkeys()
        else:
            pattern = self.rootpath+self.delimiter
            lpattern = len(pattern)
            return (k[lpattern:] for k in self._viewkeys() if k.startswith(pattern))

    def viewitems(self):
        # Filter items to keep only the ones below the rootpath level
        if not self.rootpath:
            return self._viewitems()
        else:
            pattern = self.rootpath+self.delimiter
            lpattern = len(pattern)
            return ((k[lpattern:], v) for k,v in self._viewitems() if k.startswith(pattern))

    def viewvalues(self):
        if not self.rootpath:
            return self._viewvalues()
        else:
            pattern = self.rootpath+self.delimiter
            lpattern = len(pattern)
            return (v for k,v in self._viewitems() if k.startswith(pattern))

    iterkeys = viewkeys
    itervalues = viewvalues
    iteritems = viewitems
    if PY3:
        keys = viewkeys
        values = viewvalues
        items = viewitems
    else:
        def keys(self):
            return list(self.viewkeys())
        def values(self):
            return list(self.viewvalues())
        def items(self):
            return list(self.viewitems())

    def update(self, d2):
        return self.d.update(d2.d)

    def __eq__(self, d2):
        return (self.d == d2)

    def __repr__(self):
        # Filter the items if there is a rootpath and return as a new fdict
        if self.rootpath:
            return repr(fdict(d=dict(self.items())))
        else:
            try:
                return self.d.__repr__()
            except AttributeError as exc:
                return repr(dict(self.items()))

    def __str__(self):
        if self.rootpath:
            return str(fdict(d=dict(self.items())))
        else:
            try:
                return self.d.__str__()
            except AttributeError as exc:
                return str(dict(self.items()))

    def to_dict(self):
        return dict(self.items())

class sfdict(fdict):
    '''A nested dict with flattened internal representation, combined with shelve to allow for efficient storage and memory allocation of huge nested dictionnaries.
    If you change leaf items (eg, list.append), do not forget to sync() to commit changes to disk and empty memory cache because else this class has no way to know if leaf items were changed!
    '''
    def __init__(self, *args, **kwargs):
        if not ('filename' in kwargs):
            self.filename = None
        else:
            self.filename = kwargs['filename']
            del kwargs['filename']
        fdict.__init__(self, *args, **kwargs)
        self.d = shelve.open(filename=self.filename, flag='c', writeback=True)
        self._py3compat()

    def __setitem__(self, key, value):
        fdict.__setitem__(self, key, value)
        self.sync()

    def get_filename(self):
        return self.filename

    def sync(self):
        self.d.sync()

    def close(self):
        self.d.close()

# Unit testing
a = fdict()
a['a'] = {}
a['c']['b'] = set([1, 2])
b = a['a']

assert a.keys() == ['a', 'c/b']
assert b.items() == []
assert a.items() == [('a', {}), ('c/b', set([1, 2]))]

c = {}
c['b'] = set([1, 2])
assert c.items() == [('b', set([1, 2]))]

assert a.values() == [{}, set([1, 2])]
assert b.values() == []
assert c.values() == [set([1, 2])]

d = fdict()
d['b'] = {'a': 1}
d['c/b'] = set([2, 3, 5])
assert d.to_dict() == {'c/b': set([2, 3, 5]), 'b': {'a': 1}}

a.update(d)
assert a.to_dict() == {'a': {}, 'c/b': set([2, 3, 5]), 'b': {'a': 1}}
assert a['c'].to_dict() == {'b': set([2, 3, 5])}

g = sfdict(filename='testshelf')
g['a'] = 3
g['b/c'] = set([1, 3, 4])
g['d'] = {}
assert g == {'a': 3, 'b/c': set([1, 3, 4]), 'd': {}}

h = sfdict(filename='testshelf')
assert h == g