Source code for nxpy.core.sort.sort

# nxpy_sort -------------------------------------------------------------------

# Copyright Nicola Musatti 2010 - 2018
# Use, modification, and distribution are subject to the Boost Software
# License, Version 1.0. (See accompanying file LICENSE.txt or copy at

# See -----------------

Sort functions.


[docs]def topological_sort(pairs): r""" Provide a topological ordering of the supplied pair elements. *pairs* is a sequence of two element sequences, in which the first element comes before the second according to the desired ordering criterium. """ res = [] top = set() nodes = {} for end, start in pairs: if end not in nodes: nodes[end] = [] nodes[end].append(start) for end, start in pairs: if start not in nodes: top.add(start) while len(top) > 0: s = top.pop() res.append(s) for e in nodes: try: nodes[e].remove(s) if len(nodes[e]) == 0: top.add(e) except ValueError: pass for e in top: try: del nodes[e] except: pass if len(nodes) > 0: return None else: return res