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

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

* fixup! Format Python code with psf/black push

project_euler/problem_33/__init__.py

@@ -1 +0,0 @@
-

project_euler/problem_33/sol1.py

@@ -43,7 +43,7 @@ def solve(digit_len: int) -> str:
         while den <= 99:
             if (num != den) and (num % 10 == den // 10) and (den % 10 != 0):
                 if isDigitCancelling(num, den):
-                    solutions.append("{}/{}".format(num, den))
+                    solutions.append(f"{num}/{den}")
             den += 1
         num += 1
         den = 10