- Added solutions to the task "Permutation Ranking" of week 174.

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diff --git a/challenge-174/mohammad-anwar/python/ch-2.py b/challenge-174/mohammad-anwar/python/ch-2.py
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+#!/usr/bin/python3
+
+'''
+
+Week 174:
+
+    https://theweeklychallenge.org/blog/perl-weekly-challenge-174
+
+Task #2: Permutation Ranking
+
+    You are given a list of integers with no duplicates, e.g. [0, 1, 2].
+
+    Write two functions, permutation2rank() which will take the list
+    and determine its rank (starting at 0) in the set of possible
+    permutations arranged in lexicographic order, and rank2permutation()
+    which will take the list and a rank number and produce just that
+    permutation.
+
+'''
+
+import unittest
+import itertools
+
+def permutation2rank(array):
+    array.sort()
+    return list(itertools.permutations(array))
+
+def rank2permutation(array, rank):
+    p2r = permutation2rank(array)
+    return p2r[rank]
+
+#
+#
+# Unit test class
+
+class TestPermutationRanking(unittest.TestCase):
+    def test_permutation2rank(self):
+        exp = [ (0, 1, 2),
+                (0, 2, 1),
+                (1, 0, 2),
+                (1, 2, 0),
+                (2, 0, 1),
+                (2, 1, 0),
+              ]
+        got = permutation2rank([1, 0, 2])
+        self.assertEqual(exp, got)
+
+    def test_rank2permutation(self):
+        exp = (0, 2, 1)
+        got = rank2permutation([1, 0, 2], 1)
+        self.assertEqual(exp, got)
+
+unittest.main()