cardinality¶

cardinality is a small Python library to determine and check the size of any iterable (lists, iterators, generators, and so on). It is intended as a useful companion to the built-in itertools module.

Installation¶

pip install cardinality

Usage¶

The cardinality module provides these functions:

cardinality.count()
cardinality.at_least()
cardinality.at_most()
cardinality.between()

The API docs below contain usage examples for each function.

Note

Each function creates an iterator for the iterable that is passed to it, and consumes that iterator, but not necessarily until exhaustion. If an argument can be iterated over only once (e.g. generators), do not use the object afterwards.

API¶

cardinality.count(iterable)¶

Count the number of items that iterable yields.

Equivalent to the expression

len(iterable)

… but it also works for iterables that do not support len().

>>> import cardinality
>>> cardinality.count([1, 2, 3])
3
>>> cardinality.count(i for i in range(500))
500
>>> def gen():
...     yield 'hello'
...     yield 'world'
>>> cardinality.count(gen())
2

cardinality.at_least(size, iterable)¶

Check whether iterable yields at least size items.

Equivalent to the expression

cardinality.count(iterable) >= size

… but more efficient.

>>> import cardinality
>>> cardinality.at_least(3, range(2))
False
>>> cardinality.at_least(3, range(5))
True
>>> def gen():
...     yield 'hello'
...     yield 'world'
>>> cardinality.at_least(2, gen())
True

cardinality.at_most(size, iterable)¶

Check whether iterable yields no more than size items.

Equivalent to the expression

cardinality.count(iterable) <= size

… but more efficient.

>>> import cardinality
>>> cardinality.at_most(3, range(2))
True
>>> cardinality.at_most(3, range(5))
False
>>> def gen():
...     yield 'hello'
...     yield 'world'
>>> cardinality.at_most(1, gen())
False

cardinality.between(min, max, iterable)¶

Check whether iterable yields at least min and at most max items.

Equivalent to the expression

min <= cardinality.count(iterable) <= max

… but more efficient.

>>> import cardinality
>>> cardinality.between(4, 6, range(5))
True
>>> cardinality.between(4, 6, range(20))
False
>>> def gen():
...     yield 'hello'
...     yield 'world'
>>> cardinality.between(0, 3, gen())
True

Contributing¶

The source code and issue tracker for this package can be found on Github:

https://github.com/wbolster/cardinality

License¶

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
Neither the name of the author nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

(This is the OSI approved 3-clause “New BSD License”.)