app/django/utils/itercompat.py
author Daniel Hans <Daniel.M.Hans@gmail.com>
Tue, 03 Nov 2009 00:50:23 +0100
changeset 3075 1e78db95e38a
parent 323 ff1a9aa48cfd
permissions -rw-r--r--
getListContentForData function added to lists helper. It allows to manually set a list of entities which is to be displayed on the view. Previously, the only function was getListContent, but it retrived data on its own by a single query. The new function can be useful whenever it is impossible or very awkward to obtain entities in such a way (for example more sophisticated SQL statements). Additionally, the getListContent function is reconstructed so that it collects the data first and then calls getListContentForData.

"""
Providing iterator functions that are not in all version of Python we support.
Where possible, we try to use the system-native version and only fall back to
these implementations if necessary.
"""

import itertools

def compat_tee(iterable):
    """
    Return two independent iterators from a single iterable.

    Based on http://www.python.org/doc/2.3.5/lib/itertools-example.html
    """
    # Note: Using a dictionary and a list as the default arguments here is
    # deliberate and safe in this instance.
    def gen(next, data={}, cnt=[0]):
        dpop = data.pop
        for i in itertools.count():
            if i == cnt[0]:
                item = data[i] = next()
                cnt[0] += 1
            else:
                item = dpop(i)
            yield item
    next = iter(iterable).next
    return gen(next), gen(next)

def groupby(iterable, keyfunc=None):
    """
    Taken from http://docs.python.org/lib/itertools-functions.html
    """
    if keyfunc is None:
        keyfunc = lambda x:x
    iterable = iter(iterable)
    l = [iterable.next()]
    lastkey = keyfunc(l[0])
    for item in iterable:
        key = keyfunc(item)
        if key != lastkey:
            yield lastkey, l
            lastkey = key
            l = [item]
        else:
            l.append(item)
    yield lastkey, l

# Not really in itertools, since it's a builtin in Python 2.4 and later, but it
# does operate as an iterator.
def reversed(data):
    for index in xrange(len(data)-1, -1, -1):
        yield data[index]

if hasattr(itertools, 'tee'):
    tee = itertools.tee
else:
    tee = compat_tee
if hasattr(itertools, 'groupby'):
    groupby = itertools.groupby

def is_iterable(x):
    "A implementation independent way of checking for iterables"
    try:
        iter(x)
    except TypeError:
        return False
    else:
        return True

def sorted(in_value):
    "A naive implementation of sorted"
    out_value = in_value[:]
    out_value.sort()
    return out_value