PDicts - immutable dictionaries

Introduction

A PDict is a dictionary that is mostly like the built-in Python dictionary type:

>>> from pysistence import make_dict
>>> d = make_dict(foo='bar')
>>> d
{'foo': 'bar'}

The main difference is that this dictionary is immutable:

>>> d['asdf'] = 'jkl;'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "persistent_dict.py", line 22, in not_implemented_method
    raise NotImplementedError, 'Cannot set values in a PDict'
NotImplementedError: Cannot set values in a PDict
>>> del d['foo']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "persistent_dict.py", line 22, in not_implemented_method
    raise NotImplementedError, 'Cannot set values in a PDict'
NotImplementedError: Cannot set values in a PDict

Just like the Expando, you can make copies using the without and using methods:

>>> d2 = d.using(asdf='jkl;')
>>> d2
{'foo': 'bar', 'asdf': 'jkl;'}
>>> d3 = d2.without('foo')
>>> d3
{'asdf': 'jkl;'}

See also

Expandos - semi-persistent maps

A semi-persistent object type that is similar to the PDict.

Reference

pysistence.persistent_dict.make_dict(mapping, **kwargs)

This function works the same as the builtin dict function. You may build a PDict using a pre-existing dictionary, a sequence of two-item sequences, or using keyword arguments. This is essentially a binding to PDict‘s constructor.

class pysistence.persistent_dict.PDict(mapping, **kwargs)

Build a PDict instance. See the documentation for make_dict() for more information.

copy()

Get a new PDict that is the same as the current one.

using(**kwargs)

Get a new PDict that’s the same as the current one, but with extra items defined by kwargs.

without(*args)

Get a new PDict that’s the same as the current one, but without the keys named by args.