如何阅读键盘输入？

Question

我想在python中从键盘读取数据

我试试这个:

nb = input('Choose a number')
print ('Number%s \n' % (nb))

但它不起作用,既不是日食也不是终端,它总是停止问题.我可以输入一个数字,但没有任何事情发生.

你知道为什么吗？

Answer 1

尝试

raw_input('Enter your input:')  # If you use Python 2
input('Enter your input:')      # If you use Python 3

如果你想要一个数值,只需转换它:

try:
    mode=int(raw_input('Input:'))
except ValueError:
    print "Not a number"

Answer 2

看来你在这里混合不同的Pythons(Python 2.x与Python 3.x)......这基本上是正确的:

nb = input('Choose a number: ')

问题是它只在Python 3中得到支持.正如@sharpner所回答的那样,对于旧版本的Python(2.x),你必须使用这个函数raw_input:

nb = raw_input('Choose a number: ')

如果你想将其转换为数字,那么你应该尝试:

number = int(nb)

...虽然您需要考虑到这会引发异常:

try:
    number = int(nb)
except ValueError:
    print("Invalid number")

如果你想使用格式打印数字,str.format()建议在Python 3 中使用:

print("Number: {0}\n".format(number))

代替:

print('Number %s \n' % (nb))

但是这两个选项(str.format()和%)在Python 2.7和Python 3中都有效.

Answer 3

非阻塞,多线程示例:

由于键盘输入上的阻塞(因为input()功能块)经常不是我们想要做的(我们经常喜欢继续做其他事情),这里有一个非常精简的多线程示例来演示如何继续运行你的主要应用程序,当他们到达时仍然读取键盘输入.

这可以通过创建一个在后台运行的线程,不断调用input()然后将收到的任何数据传递给队列来实现.

通过这种方式,您的主线程可以执行任何操作,只要队列中有内容,就可以从第一个线程接收键盘输入数据.

1.裸Python 3代码示例(无评论):

import threading
import queue
import time

def read_kbd_input(inputQueue):
    print('Ready for keyboard input:')
    while (True):
        input_str = input()
        inputQueue.put(input_str)

def main():
    EXIT_COMMAND = "exit"
    inputQueue = queue.Queue()

    inputThread = threading.Thread(target=read_kbd_input, args=(inputQueue,), daemon=True)
    inputThread.start()

    while (True):
        if (inputQueue.qsize() > 0):
            input_str = inputQueue.get()
            print("input_str = {}".format(input_str))

            if (input_str == EXIT_COMMAND):
                print("Exiting serial terminal.")
                break

            # Insert your code here to do whatever you want with the input_str.

        # The rest of your program goes here.

        time.sleep(0.01) 
    print("End.")

if (__name__ == '__main__'): 
    main()

2.与上面相同的Python 3代码,但有大量的解释性注释:

"""
read_keyboard_input.py

Gabriel Staples
www.ElectricRCAircraftGuy.com
14 Nov. 2018

References:
- https://pyserial.readthedocs.io/en/latest/pyserial_api.html
- *****https://www.tutorialspoint.com/python/python_multithreading.htm
- *****https://en.wikibooks.org/wiki/Python_Programming/Threading
- https://stackoverflow.com/questions/1607612/python-how-do-i-make-a-subclass-from-a-superclass
- https://docs.python.org/3/library/queue.html
- https://docs.python.org/3.7/library/threading.html

To install PySerial: `sudo python3 -m pip install pyserial`

To run this program: `python3 this_filename.py`

"""

import threading
import queue
import time

def read_kbd_input(inputQueue):
    print('Ready for keyboard input:')
    while (True):
        # Receive keyboard input from user.
        input_str = input()

        # Enqueue this input string.
        # Note: Lock not required here since we are only calling a single Queue method, not a sequence of them 
        # which would otherwise need to be treated as one atomic operation.
        inputQueue.put(input_str)

def main():

    EXIT_COMMAND = "exit" # Command to exit this program

    # The following threading lock is required only if you need to enforce atomic access to a chunk of multiple queue
    # method calls in a row.  Use this if you have such a need, as follows:
    # 1. Pass queueLock as an input parameter to whichever function requires it.
    # 2. Call queueLock.acquire() to obtain the lock.
    # 3. Do your series of queue calls which need to be treated as one big atomic operation, such as calling
    # inputQueue.qsize(), followed by inputQueue.put(), for example.
    # 4. Call queueLock.release() to release the lock.
    # queueLock = threading.Lock() 

    #Keyboard input queue to pass data from the thread reading the keyboard inputs to the main thread.
    inputQueue = queue.Queue()

    # Create & start a thread to read keyboard inputs.
    # Set daemon to True to auto-kill this thread when all other non-daemonic threads are exited. This is desired since
    # this thread has no cleanup to do, which would otherwise require a more graceful approach to clean up then exit.
    inputThread = threading.Thread(target=read_kbd_input, args=(inputQueue,), daemon=True)
    inputThread.start()

    # Main loop
    while (True):

        # Read keyboard inputs
        # Note: if this queue were being read in multiple places we would need to use the queueLock above to ensure
        # multi-method-call atomic access. Since this is the only place we are removing from the queue, however, in this
        # example program, no locks are required.
        if (inputQueue.qsize() > 0):
            input_str = inputQueue.get()
            print("input_str = {}".format(input_str))

            if (input_str == EXIT_COMMAND):
                print("Exiting serial terminal.")
                break # exit the while loop

            # Insert your code here to do whatever you want with the input_str.

        # The rest of your program goes here.

        # Sleep for a short time to prevent this thread from sucking up all of your CPU resources on your PC.
        time.sleep(0.01) 

    print("End.")

# If you run this Python file directly (ex: via `python3 this_filename.py`), do the following:
if (__name__ == '__main__'): 
    main()

样本输出:

$ python3 read_keyboard_input.py
准备键盘输入:
hey
input_str = hey
hello
input_str = hello
7000
input_str = 7000
exit
input_str = exit
退出串行终端.
结束.

参考文献:

1. https://pyserial.readthedocs.io/en/latest/pyserial_api.html
2. *****https://www.tutorialspoint.com/python/python_multithreading.htm
3. *****https://en.wikibooks.org/wiki/Python_Programming/Threading
4. Python:如何从超类创建子类？
5. https://docs.python.org/3/library/queue.html
6. https://docs.python.org/3.7/library/threading.html