This is the same solution but with Return Early, many programmers myself included find this more readable.

class Solution:
  def diffWaysToEvaluateExpression(self, input):
    result = []
    
    # return early instead of using else condition
    if "+" not in input and "*" not in input and "-" not in input:
      result.append(int(input))
      return result

    # continue program if condition is not met
    for i in range(len(input)):
      char = input[i]
      if char.isdigit():
        # this also avoids nesting
        continue

      left_part = self.diffWaysToEvaluateExpression(input[0:i])
      right_part = self.diffWaysToEvaluateExpression(input[i+1:])

      for part_1 in left_part:
        for part_2 in right_part:
          if char == "+":
            result.append(int(part_1 + part_2))
          elif char == "*":
            result.append(int(part_1 * part_2))
          elif char == "-":
            result.append(int(part_1 - part_2))

    return result