Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

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Iterators

In C++, and STL in particular, we see iterators everywhere. Python also has iterators, but these are two very different beasts.

C++ iterators:

Python Iterators:

The typical Python iteration protocol: for y in x... is as follows:

iter = x.__iter__()         # get iterator
try:
    while 1:
    y = iter.next()         # get each item
    ...                     # process y
except StopIteration: pass  # iterator exhausted

Boost.Python provides some mechanisms to make C++ iterators play along nicely as Python iterators. What we need to do is to produce appropriate _iter_ function from C++ iterators that is compatible with the Python iteration protocol. For example:

object get_iterator = iterator<vector<int> >();
object iter = get_iterator(v);
object first = iter.next();

Or for use in class_<>:

.def("__iter__", iterator<vector<int> >())

range

We can create a Python savvy iterator using the range function:

Here, start/finish may be one of:

iterator

Given a container T, iterator is a shortcut that simply calls range with &T::begin, &T::end.

Let's put this into action... Here's an example from some hypothetical bogon Particle accelerator code:

f = Field()
for x in f.pions:
    smash(x)
for y in f.bogons:
    count(y)

Now, our C++ Wrapper:

class_<F>("Field")
    .property("pions", range(&F::p_begin, &F::p_end))
    .property("bogons", range(&F::b_begin, &F::b_end));
Copyright © 2002-2004 Joel de Guzman, David Abrahams

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