|Version 1 (modified by cmlenz, 10 years ago) (diff)|
Helper functions for use in Markup templates
Often you need non-trivial presentation logic in templates, but Markup does not (yet) let you drop into straight Python. In Markup, such presentation logic must be either performed in the controller (i.e. the Python code feeding the template with date), or in helper functions that are called from within template expressions.
This page serves as a place where generalized functions that solve common tasks in presentation logic can be collected. At some point, Markup might include a library of such functions.
Python Standard Library
Many of the Python builtin functions (such as reversed or sorted), as well as those in the itertools package (such as groupby), can be quite useful in templates. The builtin functions are available by default, whereas other functions need to be put in the template context data explicitly.
def group(iterable, num, predicate=None): """Combines the elements produced by the given iterable so that every `n` items are returned as a tuple. >>> items = [1, 2, 3, 4] >>> for item in group(items, 2): ... print item (1, 2) (3, 4) The last tuple is padded with `None` values if its' length is smaller than `num`. >>> items = [1, 2, 3, 4, 5] >>> for item in group(items, 2): ... print item (1, 2) (3, 4) (5, None) The optional `predicate` parameter can be used to flag elements that should not be packed together with other items. Only those elements where the predicate function returns True are grouped with other elements, otherwise they are returned as a tuple of length 1: >>> items = [1, 2, 3, 4] >>> for item in group(items, 2, lambda x: x != 3): ... print item (1, 2) (3,) (4, None) """ buf =  for item in iterable: flush = predicate and not predicate(item) if buf and flush: buf += [None] * (num - len(buf)) yield tuple(buf) del buf[:] buf.append(item) if flush or len(buf) == num: yield tuple(buf) del buf[:] if buf: buf += [None] * (num - len(buf)) yield tuple(buf)
If the predicate functionality is not needed, a vastly simpler implementation of that function would be:
def group(iterable, num): """Group an iterable into an n-tuples iterable. Incomplete tuples are discarded e.g. >>> list(group(range(10), 3)) [(0, 1, 2), (3, 4, 5), (6, 7, 8), (9, None, None)] """ return map(None, *[iter(iterable)] * num)
See also the Python Cookbook recipe “Group a list into sequential n-tuples”.