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"""
Helper for looping over sequences, particular in templates.
Often in a loop in a template it's handy to know what's next up,
previously up, if this is the first or last item in the sequence, etc.
These can be awkward to manage in a normal Python loop, but using the
looper you can get a better sense of the context. Use like::
>>> for loop, item in looper(['a', 'b', 'c']):
... print loop.number, item
... if not loop.last:
... print '---'
1 a
---
2 b
---
3 c
"""
import sys
from .compat3 import basestring_
__all__ = ['looper']
class looper:
"""
Helper for looping (particularly in templates)
Use this like::
for loop, item in looper(seq):
if loop.first:
...
"""
def __init__(self, seq):
self.seq = seq
def __iter__(self):
return looper_iter(self.seq)
def __repr__(self):
return '<%s for %r>' % (
self.__class__.__name__, self.seq)
class looper_iter:
def __init__(self, seq):
self.seq = list(seq)
self.pos = 0
def __iter__(self):
return self
def __next__(self):
if self.pos >= len(self.seq):
raise StopIteration
result = loop_pos(self.seq, self.pos), self.seq[self.pos]
self.pos += 1
return result
class loop_pos:
def __init__(self, seq, pos):
self.seq = seq
self.pos = pos
def __repr__(self):
return '<loop pos=%r at %r>' % (
self.seq[self.pos], self.pos)
@property
def index(self):
return self.pos
@property
def number(self):
return self.pos + 1
@property
def item(self):
return self.seq[self.pos]
@property
def __next__(self):
try:
return self.seq[self.pos + 1]
except IndexError:
return None
@property
def previous(self):
if self.pos == 0:
return None
return self.seq[self.pos - 1]
@property
def odd(self):
return not self.pos % 2
@property
def even(self):
return self.pos % 2
@property
def first(self):
return self.pos == 0
@property
def last(self):
return self.pos == len(self.seq) - 1
@property
def length(self):
return len(self.seq)
def first_group(self, getter=None):
"""
Returns true if this item is the start of a new group,
where groups mean that some attribute has changed. The getter
can be None (the item itself changes), an attribute name like
``'.attr'``, a function, or a dict key or list index.
"""
if self.first:
return True
return self._compare_group(self.item, self.previous, getter)
def last_group(self, getter=None):
"""
Returns true if this item is the end of a new group,
where groups mean that some attribute has changed. The getter
can be None (the item itself changes), an attribute name like
``'.attr'``, a function, or a dict key or list index.
"""
if self.last:
return True
return self._compare_group(self.item, self.__next__, getter)
def _compare_group(self, item, other, getter):
if getter is None:
return item != other
elif (isinstance(getter, basestring_) and getter.startswith('.')):
getter = getter[1:]
if getter.endswith('()'):
getter = getter[:-2]
return getattr(item, getter)() != getattr(other, getter)()
else:
return getattr(item, getter) != getattr(other, getter)
elif hasattr(getter, '__call__'):
return getter(item) != getter(other)
else:
return item[getter] != other[getter]
|
