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"""Processor for field value truncation.
"""
def _truncate_right(value, length, marker):
if len(value) <= length:
short = value
elif marker:
nchars_free = length - len(marker)
if nchars_free > 0:
short = value[:nchars_free] + marker
else:
short = marker[:length]
else:
short = value[:length]
return short
def _truncate_left(value, length, marker):
res = _truncate_right(value[::-1], length,
marker[::-1] if marker else None)
return res[::-1]
def _splice(value, n):
"""Splice `value` at its center, retaining a total of `n` characters.
Parameters
----------
value : str
n : int
The total length of the returned ends will not be greater than this
value. Characters will be dropped from the center to reach this limit.
Returns
-------
A tuple of str: (head, tail).
"""
if n <= 0:
raise ValueError("n must be positive")
value_len = len(value)
center = value_len // 2
left, right = value[:center], value[center:]
if n >= value_len:
return left, right
n_todrop = value_len - n
right_idx = n_todrop // 2
left_idx = right_idx + n_todrop % 2
return left[:-left_idx], right[right_idx:]
def _truncate_center(value, length, marker):
value_len = len(value)
if value_len <= length:
return value
if marker:
marker_len = len(marker)
if marker_len < length:
left, right = _splice(value, length - marker_len)
parts = left, marker, right
else:
parts = _splice(marker, length)
else:
parts = _splice(value, length)
return "".join(parts)
class Truncater(object):
"""A processor that truncates the result to a given length.
Note: You probably want to place the `truncate` method at the beginning of
the processor list so that the truncation is based on the length of the
original value.
Parameters
----------
length : int
Truncate the string to this length.
marker : str or bool, optional
Indicate truncation with this string. If True, indicate truncation by
replacing the last three characters of a truncated string with '...'.
If False, no truncation marker is added to a truncated string.
where : {'left', 'center', 'right'}, optional
Where to truncate the result.
"""
def __init__(self, length, marker=True, where="right"):
self.length = length
self.marker = "..." if marker is True else marker
truncate_fns = {"left": _truncate_left,
"center": _truncate_center,
"right": _truncate_right}
try:
self._truncate_fn = truncate_fns[where]
except KeyError:
raise ValueError("Unrecognized `where` value: {}".format(where))
def truncate(self, _, result):
return self._truncate_fn(result, self.length, self.marker)
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