Avoid mutable default arguments

Author: cclauss

Diff for: graphs/eulerian_path_and_circuit_for_undirected_graph.py

@@ -6,8 +6,8 @@
 
 
 # using dfs for finding eulerian path traversal
-def dfs(u, graph, visited_edge, path=[]):
-    path = path + [u]
+def dfs(u, graph, visited_edge, path=None):
+    path = (path or []) + [u]
     for v in graph[u]:
         if visited_edge[u][v] is False:
             visited_edge[u][v], visited_edge[v][u] = True, True

Diff for: graphs/frequent_pattern_graph_miner.py

@@ -168,11 +168,11 @@ def construct_graph(cluster, nodes):
     return graph
 
 
-def myDFS(graph, start, end, path=[]):
+def myDFS(graph, start, end, path=None):
     """
     find different DFS walk from given node to Header node
     """
-    path = path + [start]
+    path = (path or []) + [start]
     if start == end:
         paths.append(path)
     for node in graph[start]:

Diff for: maths/radix2_fft.py

@@ -49,10 +49,10 @@ class FFT:
     A*B = 0*x^(-0+0j) + 1*x^(2+0j) + 2*x^(3+0j) + 3*x^(8+0j) + 4*x^(6+0j) + 5*x^(8+0j)
     """
 
-    def __init__(self, polyA=[0], polyB=[0]):
+    def __init__(self, polyA=None, polyB=None):
         # Input as list
-        self.polyA = list(polyA)[:]
-        self.polyB = list(polyB)[:]
+        self.polyA = list(polyA or [])[:]
+        self.polyB = list(polyB or [])[:]
 
         # Remove leading zero coefficients
         while self.polyA[-1] == 0: