flats module

Minimal library that enables flattening of nested instances of iterable containers.

flats(xss, depth=1)

Flatten an instance of a container type that is the root of a tree of nested instances of container types, returning as an Iterable the sequence of all objects or values (that are not of a container type) encountered during an in-order traversal.

Parameters:

• xss (Iterable) – Iterable (usually of container instances) to be flattened.

• depth (Optional[int]) – Number of layers to flatten (i.e., amount by which the depth of the nested structure should be reduced).

Return type:

Iterable

>>> list(flats([[1, 2, 3], [4, 5, 6, 7]]))
[1, 2, 3, 4, 5, 6, 7]

Any instance of Iterable or GeneratorType (including instances of the built-in types tuple, list, set, frozenset, range, bytes, and bytearray) is considered an instance of a container type.

>>> list(flats(frozenset({frozenset({1, 2, 3}), frozenset({4, 5, 6, 7})})))
[1, 2, 3, 4, 5, 6, 7]
>>> list(flats(((1, 2, 3), (4, 5, 6, 7))))
[1, 2, 3, 4, 5, 6, 7]

The nested instances need not be of the same type.

>>> list(flats([(1, 2, 3), (4, 5, 6, 7)]))
[1, 2, 3, 4, 5, 6, 7]
>>> tuple(flats([{1}, {2}, {3}, frozenset({4}), iter([5, 6, 7])]))
(1, 2, 3, 4, 5, 6, 7)
>>> list(flats(['abc', 'xyz']))
['a', 'b', 'c', 'x', 'y', 'z']
>>> list(flats([range(3), range(3)]))
[0, 1, 2, 0, 1, 2]
>>> list(flats([bytes([0, 1, 2]), bytes([3, 4, 5])]))
[0, 1, 2, 3, 4, 5]
>>> list(flats([bytearray([0, 1, 2]), bytearray([3, 4, 5])]))
[0, 1, 2, 3, 4, 5]

The optional depth argument can be used to limit the depth at which nested instances of a container type are not recursively traversed. For example, setting depth to 1 is sufficient to flatten any list of lists into a list. Thus, 1 is the default value for depth.

>>> list(flats([[[1, 2], 3], [4, 5, 6, 7]], depth=1))
[[1, 2], 3, 4, 5, 6, 7]
>>> list(flats([[[1, 2], 3], [4, 5, 6, 7]], depth=2))
[1, 2, 3, 4, 5, 6, 7]
>>> list(flats([[[1, 2], [3]], [[4, 5], [6, 7]]], depth=2))
[1, 2, 3, 4, 5, 6, 7]
>>> list(flats([(1, 2, 3), (4, 5, 6, 7)], depth=3))
[1, 2, 3, 4, 5, 6, 7]

Setting depth to 0 returns unmodified the contents of the supplied instance of a container type (though, for consistency, these results are still returned as an iterable).

>>> list(flats([[[1, 2], 3], [4, 5, 6, 7]], depth=0))
[[[1, 2], 3], [4, 5, 6, 7]]

If depth is set to float('inf'), recursive traversal of instances of container types occurs to any depth (until an instance of a non-container type is encountered).

>>> list(flats([[[1, [2]], 3], [4, [[[5]]], 6, 7]], depth=float('inf')))
[1, 2, 3, 4, 5, 6, 7]

If the value of the depth argument is not a non-negative integer, an exception is raised.

>>> list(flats([(1, 2, 3), (4, 5, 6, 7)], depth='abc'))
Traceback (most recent call last):
  ...
TypeError: depth must be an integer or infinity
>>> list(flats([(1, 2, 3), (4, 5, 6, 7)], depth=-1))
Traceback (most recent call last):
  ...
ValueError: depth must be a non-negative integer or infinity

User-defined container types are also supported.

>>> class wrap():
...     def __init__(self, xs): self.xs = xs
...     def __getitem__(self, key): return self.xs[key]
...     def __repr__(self): return 'wrap(' + str(self.xs) + ')'
>>> wrap(list(flats(wrap([wrap([1, 2]), wrap([3, 4])]))))
wrap([1, 2, 3, 4])