Viewing file:  view.py (1.5 KB) -rw-r--r--
Select action/file-type:
 (+) |  (+) |  (+) | Code (+) | Session (+) |  (+) | SDB (+) |  (+) |  (+) |  (+) |  (+) |  (+) |
# -*- test-case-name: epsilon.test.test_view -*-
"""
Utility functionality for creating wrapping sequences so as to transform
their indices in some manner.
"""
class SlicedView(object):
"""
Wrapper around a sequence which allows indexing and non-extended
slicing, adjusting all indices using a transformation defined by a
L{slice} object.
For example::
s = ['a', 'b']
t = SlicedView(s, slice(1, None))
t[0] == 'b'
@ivar sequence: The underlying sequence from which to retrieve elements.
@ivar bounds: A C{slice} instance defining the boundaries of this view.
"""
def __init__(self, sequence, bounds):
self.sequence = sequence
self.bounds = bounds
def _getIndices(self):
start, stop, step = self.bounds.indices(len(self.sequence))
indices = xrange(start, stop, step)
return indices
def __getitem__(self, index):
"""
Compute the index in the underlying sequence of the given view index
and return the corresponding element.
@raise IndexError: If C{index} is out of bounds for the view.
@raise ValueError: If C{self.bounds} is out of bounds for
C{self.sequence}.
"""
if isinstance(index, slice):
return SlicedView(self, index)
return self.sequence[self._getIndices()[index]]
def __len__(self):
"""
Compute the length of this view onto the sequence and return it.
"""
return len(self._getIndices())
|