try-except

position = [
['2019-05-01', '- 6'],
['2019-05-02', '+5'],
['2019-05-03', ' 5'],
['2019-05-04', '4'],
['2019-05-05', '5'],
['2019-05-06', '5'],
['2019-05-07', '4'],
['2019-05-08', 'Error 5'],
['2019-05-09', '3'],
['2019-05-10', '3'],
]

total_position = 0
count_lines = 0
wrong_lines_content = []

for row in position:
    try:
        count_lines += 1
        level = int(row[1])
        total_position += level
    except:
        wrong_lines = 1
        wrong_lines_content.append(row[1])
print('Количество измерений', count_lines)
print('Некорректные строки', wrong_lines_content)