pyupgrade --py37-plus **/*.py (#1654)

* pyupgrade --py37-plus **/*.py

* fixup! Format Python code with psf/black push

graphs/basic_graphs.py

@@ -48,7 +48,7 @@ if __name__ == "__main__":
 
 
 def dfs(G, s):
-    vis, S = set([s]), [s]
+    vis, S = {s}, [s]
     print(s)
     while S:
         flag = 0
@@ -76,7 +76,7 @@ from collections import deque
 
 
 def bfs(G, s):
-    vis, Q = set([s]), deque([s])
+    vis, Q = {s}, deque([s])
     print(s)
     while Q:
         u = Q.popleft()
@@ -255,7 +255,7 @@ def krusk(E_and_n):
     # Sort edges on the basis of distance
     (E, n) = E_and_n
     E.sort(reverse=True, key=lambda x: x[2])
-    s = [set([i]) for i in range(1, n + 1)]
+    s = [{i} for i in range(1, n + 1)]
     while True:
         if len(s) == 1:
             break