1 files changed, 152 insertions, 0 deletions
diff --git a/tempita/_looper.py b/tempita/_looper.py
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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
+
+"""
+
+__all__ = ['looper']
+
+class looper(object):
+    """
+    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(object):
+
+    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(object):
+
+    def __init__(self, seq, pos):
+        self.seq = seq
+        self.pos = pos
+
+    def __repr__(self):
+        return '<loop pos=%r at %r>' % (
+            self.seq[pos], pos)
+
+    def index(self):
+        return self.pos
+    index = property(index)
+
+    def number(self):
+        return self.pos + 1
+    number = property(number)
+
+    def item(self):
+        return self.seq[self.pos]
+    item = property(item)
+
+    def next(self):
+        try:
+            return self.seq[self.pos+1]
+        except IndexError:
+            return None
+    next = property(next)
+
+    def previous(self):
+        if self.pos == 0:
+            return None
+        return self.seq[self.pos-1]
+    previous = property(previous)
+
+    def odd(self):
+        return not self.pos % 2
+    odd = property(odd)
+
+    def even(self):
+        return self.pos % 2
+    even = property(even)
+
+    def first(self):
+        return self.pos == 0
+    first = property(first)
+
+    def last(self):
+        return self.pos == len(self.seq)-1
+    last = property(last)
+
+    def length(self):
+        return len(self.seq)
+    length = property(length)
+
+    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 callable(getter):
+            return getter(item) != getter(other)
+        else:
+            return item[getter] != other[getter]
+