third_party/cython/src/Cython/Tempita/_looper.py

   1 """
   2 Helper for looping over sequences, particular in templates.
   3
   4 Often in a loop in a template it's handy to know what's next up,
   5 previously up, if this is the first or last item in the sequence, etc.
   6 These can be awkward to manage in a normal Python loop, but using the
   7 looper you can get a better sense of the context.  Use like::
   8
   9     >>> for loop, item in looper(['a', 'b', 'c']):
  10     ...     print loop.number, item
  11     ...     if not loop.last:
  12     ...         print '---'
  13     1 a
  14     ---
  15     2 b
  16     ---
  17     3 c
  18
  19 """
  20
  21 import sys
  22 from Cython.Tempita.compat3 import basestring_
  23
  24 __all__ = ['looper']
  25
  26
  27 class looper(object):
  28     """
  29     Helper for looping (particularly in templates)
  30
  31     Use this like::
  32
  33         for loop, item in looper(seq):
  34             if loop.first:
  35                 ...
  36     """
  37
  38     def __init__(self, seq):
  39         self.seq = seq
  40
  41     def __iter__(self):
  42         return looper_iter(self.seq)
  43
  44     def __repr__(self):
  45         return '<%s for %r>' % (
  46             self.__class__.__name__, self.seq)
  47
  48
  49 class looper_iter(object):
  50
  51     def __init__(self, seq):
  52         self.seq = list(seq)
  53         self.pos = 0
  54
  55     def __iter__(self):
  56         return self
  57
  58     def __next__(self):
  59         if self.pos >= len(self.seq):
  60             raise StopIteration
  61         result = loop_pos(self.seq, self.pos), self.seq[self.pos]
  62         self.pos += 1
  63         return result
  64
  65     if sys.version < "3":
  66         next = __next__
  67
  68
  69 class loop_pos(object):
  70
  71     def __init__(self, seq, pos):
  72         self.seq = seq
  73         self.pos = pos
  74
  75     def __repr__(self):
  76         return '<loop pos=%r at %r>' % (
  77             self.seq[self.pos], self.pos)
  78
  79     def index(self):
  80         return self.pos
  81     index = property(index)
  82
  83     def number(self):
  84         return self.pos + 1
  85     number = property(number)
  86
  87     def item(self):
  88         return self.seq[self.pos]
  89     item = property(item)
  90
  91     def __next__(self):
  92         try:
  93             return self.seq[self.pos + 1]
  94         except IndexError:
  95             return None
  96     __next__ = property(__next__)
  97
  98     if sys.version < "3":
  99         next = __next__
 100
 101     def previous(self):
 102         if self.pos == 0:
 103             return None
 104         return self.seq[self.pos - 1]
 105     previous = property(previous)
 106
 107     def odd(self):
 108         return not self.pos % 2
 109     odd = property(odd)
 110
 111     def even(self):
 112         return self.pos % 2
 113     even = property(even)
 114
 115     def first(self):
 116         return self.pos == 0
 117     first = property(first)
 118
 119     def last(self):
 120         return self.pos == len(self.seq) - 1
 121     last = property(last)
 122
 123     def length(self):
 124         return len(self.seq)
 125     length = property(length)
 126
 127     def first_group(self, getter=None):
 128         """
 129         Returns true if this item is the start of a new group,
 130         where groups mean that some attribute has changed.  The getter
 131         can be None (the item itself changes), an attribute name like
 132         ``'.attr'``, a function, or a dict key or list index.
 133         """
 134         if self.first:
 135             return True
 136         return self._compare_group(self.item, self.previous, getter)
 137
 138     def last_group(self, getter=None):
 139         """
 140         Returns true if this item is the end of a new group,
 141         where groups mean that some attribute has changed.  The getter
 142         can be None (the item itself changes), an attribute name like
 143         ``'.attr'``, a function, or a dict key or list index.
 144         """
 145         if self.last:
 146             return True
 147         return self._compare_group(self.item, self.__next__, getter)
 148
 149     def _compare_group(self, item, other, getter):
 150         if getter is None:
 151             return item != other
 152         elif (isinstance(getter, basestring_)
 153               and getter.startswith('.')):
 154             getter = getter[1:]
 155             if getter.endswith('()'):
 156                 getter = getter[:-2]
 157                 return getattr(item, getter)() != getattr(other, getter)()
 158             else:
 159                 return getattr(item, getter) != getattr(other, getter)
 160         elif hasattr(getter, '__call__'):
 161             return getter(item) != getter(other)
 162         else:
 163             return item[getter] != other[getter]