### diff env/lib/python3.9/site-packages/galaxy/util/topsort.py @ 0:4f3585e2f14bdraftdefaulttip

author shellac Mon, 22 Mar 2021 18:12:50 +0000
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```--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/env/lib/python3.9/site-packages/galaxy/util/topsort.py	Mon Mar 22 18:12:50 2021 +0000
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+"""
+Topological sort.
+
+From Tim Peters, see:
+   http://mail.python.org/pipermail/python-list/1999-July/006660.html
+
+topsort takes a list of pairs, where each pair (x, y) is taken to
+mean that x <= y wrt some abstract partial ordering.  The return
+value is a list, representing a total ordering that respects all
+the input constraints.
+E.g.,
+
+   topsort( [(1,2), (3,3)] )
+
+Valid topological sorts would be any of (but nothing other than)
+
+   [3, 1, 2]
+   [1, 3, 2]
+   [1, 2, 3]
+
+... however this variant ensures that 'key' order (first element of
+tuple) is preserved so the following will be result returned:
+
+   [1, 3, 2]
+
+because those are the permutations of the input elements that
+respect the "1 precedes 2" and "3 precedes 3" input constraints.
+Note that a constraint of the form (x, x) is really just a trick
+to make sure x appears *somewhere* in the output list.
+
+If there's a cycle in the constraints, say
+
+   topsort( [(1,2), (2,1)] )
+
+then CycleError is raised, and the exception object supports
+many methods to help analyze and break the cycles.  This requires
+a good deal more code than topsort itself!
+"""
+
+
+class CycleError(Exception):
+    def __init__(self, sofar, numpreds, succs):
+        Exception.__init__(self, "cycle in constraints",
+                           sofar, numpreds, succs)
+        self.preds = None
+
+    # return as much of the total ordering as topsort was able to
+    # find before it hit a cycle
+    def get_partial(self):
+        return self
+
+    # return remaining elt -> count of predecessors map
+    def get_pred_counts(self):
+        return self
+
+    # return remaining elt -> list of successors map
+    def get_succs(self):
+        return self
+
+    # return remaining elements (== those that don't appear in
+    # get_partial())
+    def get_elements(self):
+        return self.get_pred_counts().keys()
+
+    # Return a list of pairs representing the full state of what's
+    # CycleError again, and if you invoke get_pairlist on *that*
+    # exception object, the result will be isomorphic to *this*
+    # invocation of get_pairlist).
+    # The idea is that you can use pick_a_cycle to find a cycle,
+    # through some means or another pick an (x,y) pair in the cycle
+    # you no longer want to respect, then remove that pair from the
+    # output of get_pairlist and try topsort again.
+    def get_pairlist(self):
+        succs = self.get_succs()
+        for x in self.get_elements():
+            if x in succs:
+                for y in succs[x]:
+            else:
+                # make sure x appears in topsort's output!
+
+    # return remaining elt -> list of predecessors map
+    def get_preds(self):
+        if self.preds is not None:
+            return self.preds
+        self.preds = preds = {}
+        remaining_elts = self.get_elements()
+        for x in remaining_elts:
+            preds[x] = []
+        succs = self.get_succs()
+
+        for x in remaining_elts:
+            if x in succs:
+                for y in succs[x]:
+                    preds[y].append(x)
+
+        if __debug__:
+            for x in remaining_elts:
+                assert len(preds[x]) > 0
+        return preds
+
+    # return a cycle [x, ..., x] at random
+    def pick_a_cycle(self):
+        remaining_elts = self.get_elements()
+
+        # We know that everything in remaining_elts has a predecessor,
+        # but don't know that everything in it has a successor.  So
+        # crawling forward over succs may hit a dead end.  Instead we
+        # crawl backward over the preds until we hit a duplicate, then
+        # reverse the path.
+        preds = self.get_preds()
+        from random import choice
+        x = choice(remaining_elts)
+        index = {}
+            x = choice(preds[x])
+
+
+def _numpreds_and_successors_from_pairlist(pairlist):
+    numpreds = {}   # elt -> # of predecessors
+    successors = {}  # elt -> list of successors
+    for first, second in pairlist:
+        # make sure every elt is a key in numpreds
+        if first not in numpreds:
+            numpreds[first] = 0
+        if second not in numpreds:
+            numpreds[second] = 0
+
+        # if they're the same, there's no real dependence
+        if first == second:
+            continue
+
+        # since first < second, second gains a pred ...
+        numpreds[second] = numpreds[second] + 1
+
+        # ... and first gains a succ
+        if first in successors:
+            successors[first].append(second)
+        else:
+            successors[first] = [second]
+    return numpreds, successors
+
+
+def topsort(pairlist):
+    numpreds, successors = _numpreds_and_successors_from_pairlist(pairlist)
+
+    # suck up everything without a predecessor
+    answer = [x for x in numpreds.keys() if numpreds[x] == 0]
+
+    # for everything in answer, knock down the pred count on
+    # its successors; note that answer grows *in* the loop
+        assert numpreds[x] == 0
+        del numpreds[x]
+        if x in successors:
+            for y in successors[x]:
+                numpreds[y] = numpreds[y] - 1
+                if numpreds[y] == 0:
+            # following "del" isn't needed; just makes
+            # CycleError details easier to grasp
+            del successors[x]
+
+    if numpreds:
+        # everything in numpreds has at least one predecessor ->
+        # there's a cycle
+        if __debug__:
+            for x in numpreds.keys():
+                assert numpreds[x] > 0
+
+
+def topsort_levels(pairlist):
+    numpreds, successors = _numpreds_and_successors_from_pairlist(pairlist)
+
+
+    while 1:
+        # Suck up everything without a predecessor.
+        levparents = [x for x in numpreds.keys() if numpreds[x] == 0]
+        if not levparents:
+            break