# f = open('test.txt', 'w+')

# f.write('hello world. morning.')

# f.seek(0)

# print(f.read()) # hello world.

#

# f = open('test.txt', 'r')

# lines = f.readlines()

# print(lines)

# f.close()

# 事实上，我们可以将 f 放在一个循环中，得到它每一行的内容：

# f = open('test.txt')

# for line in f:

# print(line)

# f.close()

import os

import math

# f = open('binary.bin', 'wb')

# f.write(os.urandom(10))

# f.close()

# while True:

# try:

# text = input('>')

# if text[0] == 'q':

# break

# x = float(text)

# y = 1 / math.log10(x)

# print('y', y)

# print("1/log10({0}) = {1}".format(x, y))

# except ValueError:

# print("value must bigger than 0")

# except ZeroDivisionError:

# print("the value must not be 1")

class CommandError(ValueError):

print("bad command operation. must input 'start', 'stop', 'pause'")

valid_commands = {'start', 'stop', 'pause'}

while True:

command = input('>')

if command == 'q':

break

try:

if command.lower() not in valid_commands:

raise CommandError('Invaild command: %s' % command)

print('input command:', command)

except CommandError:

print("bad command string: %s" % command)

finally:

print('finally was called.')