# nltk.translate.Alignment¶

class nltk.translate.Alignment[source]

Bases: frozenset

A storage class for representing alignment between two sequences, s1, s2. In general, an alignment is a set of tuples of the form (i, j, …) representing an alignment between the i-th element of s1 and the j-th element of s2. Tuples are extensible (they might contain additional data, such as a boolean to indicate sure vs possible alignments).

>>> from nltk.translate import Alignment
>>> a = Alignment([(0, 0), (0, 1), (1, 2), (2, 2)])
>>> a.invert()
Alignment([(0, 0), (1, 0), (2, 1), (2, 2)])
>>> print(a.invert())
0-0 1-0 2-1 2-2
>>> a[0]
[(0, 1), (0, 0)]
>>> a.invert()[2]
[(2, 1), (2, 2)]
>>> b = Alignment([(0, 0), (0, 1)])
>>> b.issubset(a)
True
>>> c = Alignment.fromstring('0-0 0-1')
>>> b == c
True
static __new__(cls, pairs)[source]
classmethod fromstring(s)[source]

Read a giza-formatted string and return an Alignment object.

>>> Alignment.fromstring('0-0 2-1 9-2 21-3 10-4 7-5')
Alignment([(0, 0), (2, 1), (7, 5), (9, 2), (10, 4), (21, 3)])
Parameters

s (str) – the positional alignments in giza format

Return type

Alignment

Returns

An Alignment object corresponding to the string representation s.

invert()[source]

Return an Alignment object, being the inverted mapping.

range(positions=None)[source]

Work out the range of the mapping from the given positions. If no positions are specified, compute the range of the entire mapping.

copy()

Return a shallow copy of a set.

difference()

Return the difference of two or more sets as a new set.

(i.e. all elements that are in this set but not the others.)

intersection()

Return the intersection of two sets as a new set.

(i.e. all elements that are in both sets.)

isdisjoint()

Return True if two sets have a null intersection.

issubset()

Report whether another set contains this set.

issuperset()

Report whether this set contains another set.

symmetric_difference()

Return the symmetric difference of two sets as a new set.

(i.e. all elements that are in exactly one of the sets.)

union()

Return the union of sets as a new set.

(i.e. all elements that are in either set.)