Problem:
M-kun is a competitor in AtCoder, whose highest rating is X.   In this site, a competitor is given a _kyu_ (class) according to his/her highest rating. For ratings from 400 through 1999, the following kyus are given:    * From 400 through 599: 8-kyu   * From 600 through 799: 7-kyu   * From 800 through 999: 6-kyu   * From 1000 through 1199: 5-kyu   * From 1200 through 1399: 4-kyu   * From 1400 through 1599: 3-kyu   * From 1600 through 1799: 2-kyu   * From 1800 through 1999: 1-kyu  What kyu does M-kun have?

Incorrect submission (verdict: Wrong Answer):
# m-solutions2020_a.py


global FLAG_LOG
FLAG_LOG = False


def log(value):
    # FLAG_LOG = True
    # FLAG_LOG = False
    if FLAG_LOG:
        print(str(value))


def calculation(lines):
    X = int(lines[0])

    if X < 600:
        ret = 8
    elif X < 800:
        ret = 7
    elif X < 1000:
        ret = 6
    elif X < 1200:
        ret = 5
    elif X < 1400:
        ret = 4
    elif X < 1600:
        ret = 3
    elif X < 1800:
        ret = 2
    else:
        ret = 1

    return [ret]



def get_input_lines(lines_count):
    lines = list()
    for _ in range(lines_count):
        lines.append(input())
    return lines



def get_testdata(pattern):
    if pattern == 1:
        lines_input = ['']
        lines_export = ['']
    if pattern == 2:
        lines_input = ['']
        lines_export = ['']
    if pattern == 3:
        lines_input = ['']
        lines_export = ['']
    return lines_input, lines_export



def get_mode():
    import sys
    args = sys.argv
    global FLAG_LOG
    if len(args) == 1:
        mode = 0
        FLAG_LOG = False
    else:
        mode = int(args[1])
        FLAG_LOG = True
    return mode



def main():
    import time
    started = time.time()
    mode = get_mode()
    if mode == 0:
        lines_input = get_input_lines(1)
    else:
        lines_input, lines_export = get_testdata(mode)

    lines_result = calculation(lines_input)

    for line_result in lines_result:
        print(line_result)

    if mode > 0:
        print(f'lines_input=[{lines_input}]')
        print(f'lines_export=[{lines_export}]')
        print(f'lines_result=[{lines_result}]')
        if lines_result == lines_export:
            print('OK')
        else:
            print('NG')
    finished = time.time()
    duration = finished - started
    print(f'duration=[{duration}]')



if __name__ == '__main__':
    main()


Fixed, accepted submission:
# m-solutions2020_a.py


global FLAG_LOG
FLAG_LOG = False


def log(value):
    # FLAG_LOG = True
    # FLAG_LOG = False
    if FLAG_LOG:
        print(str(value))


def calculation(lines):
    X = int(lines[0])

    if X < 600:
        ret = 8
    elif X < 800:
        ret = 7
    elif X < 1000:
        ret = 6
    elif X < 1200:
        ret = 5
    elif X < 1400:
        ret = 4
    elif X < 1600:
        ret = 3
    elif X < 1800:
        ret = 2
    else:
        ret = 1

    return [ret]



def get_input_lines(lines_count):
    lines = list()
    for _ in range(lines_count):
        lines.append(input())
    return lines



def get_testdata(pattern):
    if pattern == 1:
        lines_input = [725]
        lines_export = [7]
    if pattern == 2:
        lines_input = [1600]
        lines_export = [2]
    return lines_input, lines_export



def get_mode():
    import sys
    args = sys.argv
    global FLAG_LOG
    if len(args) == 1:
        mode = 0
        FLAG_LOG = False
    else:
        mode = int(args[1])
        FLAG_LOG = True
    return mode



def main():
    
    
    mode = get_mode()
    if mode == 0:
        lines_input = get_input_lines(1)
    else:
        lines_input, lines_export = get_testdata(mode)

    lines_result = calculation(lines_input)

    for line_result in lines_result:
        print(line_result)

    if mode > 0:
        print(f'lines_input=[{lines_input}]')
        print(f'lines_export=[{lines_export}]')
        print(f'lines_result=[{lines_result}]')
        if lines_result == lines_export:
            print('OK')
        else:
            print('NG')
    # finished = time.time()
    
    # print(f'duration=[{duration}]')



if __name__ == '__main__':
    main()