使用NumPy的isnan函数检查用户输入 [英] Checking user input using isnan function of NumPy

问题描述

我正在尝试使用NumPy来检查用户输入是否为数字.我尝试使用:

I'm trying to use NumPy to check if user input is numerical. I've tried using:

import numpy as np

a = input("\n\nInsert A: ")

if np.isnan(a):
    print 'Not a number...'
else:
    print "Yep,that's a number"

就其本身而言，t可以很好地工作，但是当我将其嵌入诸如此类的函数中时:

On its own t works fine, however when I embed it into a function such as in this case:

import numpy as np

def test_this(a):   
    if np.isnan(a):
        print '\n\nThis is not an accepted type of input for A\n\n'
        raise ValueError
    else:
        print "Yep,that's a number"

a = input("\n\nInsert A: ")

test_this(a)

然后我得到一个 NotImplementationError ，说它没有为这种类型实现，有人能解释一下这是怎么工作的吗?

Then I get a NotImplementationError saying it isn't implemented for this type, can anyone explain how this is not working?

推荐答案

非数字"或"NaN"是根据IEEE-754标准的一种特殊的浮点值.函数 numpy.isnan()和 math.isnan()测试给定的浮点数是否具有此特殊值(或多个"NaN"值之一).将浮点数以外的任何内容传递给这些函数之一将导致 TypeError .

"Not a Number" or "NaN" is a special kind of floating point value according to the IEEE-754 standard. The functions numpy.isnan() and math.isnan() test if a given floating point number has this special value (or one of several "NaN" values). Passing anything else than a floating point number to one of these function results in a TypeError.

要执行您想进行的输入检查，您不应该使用 input().而是使用 raw_input()， try:将返回的字符串转换为 float ，如果失败则处理错误.

To do the kind of input checking you would like to do, you shouldn't use input(). Instead, use raw_input(),try: to convert the returned string to a float, and handle the error if this fails.

示例:

def input_float(prompt):
    while True:
        s = raw_input(prompt)
        try:
            return float(s)
        except ValueError:
            print "Please enter a valid floating point number."

@ J.F.塞巴斯蒂安指出，

As @J.F. Sebastian pointed out,

input()执行 eval(raw_input(prompt))，这很可能不是您想要的.

input() does eval(raw_input(prompt)), it's most probably not what you want.

或更明确地说， raw_input 沿字符串传递，一旦发送给 eval ，该字符串将被评估并视为带有输入值的命令而不是输入字符串本身.

Or to be more explicit, raw_input passes along a string, which once sent to eval will be evaluated and treated as though it were command with the value of the input rather than the input string itself.

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