limited-dict

This is a Python library which provides a dict-like structure which keeps elements sorted by value and maintains only the top or bottom N elements. It provides a memory efficient way of storing only the highest or lowest elements.

Installation

You can install the library using pip:

$ pip install limited_dict

Using the library

You can create the dict-like structure as follows:

from limited_dict import LimitedDict

my_dict = LimitedDict(max_length=50, cache_mapping=True, reverse_order=False)

The arguments are:

• max_length (required):

  This is the maximum number of elements to store.

• cache_mapping (optional):

  If this is True the mapping between keys and values is stored in a more efficient way. This improves performance at the expense of greater memory usage.

• reverse_order (optional):

  If this is False the elements with the lowest max_length values are maintained. If this is True the elements with the highest max_length values are maintained.

The LimitedDict class can then be used like a dict:

>>> from limited_dict import LimitedDict
>>> my_dict = LimitedDict(max_length=3, cache_mapping=False, reverse_order=False)
>>> my_dict['a'] = 1
>>> my_dict['b'] = 10
>>> my_dict['c'] = 0
>>> my_dict['d'] = 5
>>> my_dict['e'] = 7
>>> print my_dict
>>> [('c', 0), ('a', 1), ('d', 5)]

It only stores max_length elements so some elements previously specified may no longer exist in the structure. Trying to access such elements will raise a KeyError:

>>> my_dict['e']
>>> Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "limited_dict/limited_dict.py", line 48, in __getitem__
    raise KeyError(key)
KeyError: 'e'
>>> my_dict['c']
>>> 0

You can iterate over keys and values in the same way as a dict:

>>> for key, value in my_dict.items():
...    print("{key}:{value}".format(key=key, value=value))
...
...
c:0
a:1
d:5