code: def _check_conditional_statement(statement, num_collections):
          
          # Determine what the list of variables should be based on the num_collections
          correct_var = list(ascii_lowercase)[:num_collections]
  
          # Clean out the operators of the statement
          st_statement = BaseCollection._remove_operators(statement)
          parsed_st = [s for s in st_statement if s.isalpha()]
  
          # Perform the check
          for var in parsed_st:
              if var not in correct_var:
                  raise ValueError(
                      'Invalid conditional statement: {}\n '
                      'Statement should be a valid Python statement'
                      ' and the variables should be named as follows: {}'.format(
                          statement, ', '.join(correct_var))
                      )
          return correct_var
docs: Method to check conditional statements to be sure that they are valid.
  
          Args:
              statement: A conditional statement as a string (e.g. a>25 and a%5==0).
                  The variable should always be named as 'a' (without quotations).
              num_collections: An integer representing the number of data collections
                  that the statement will be evaluating.
  
          Return:
              correct_var: A list of the correct variable names that should be
                  used within the statement (eg. ['a', 'b', 'c'])