测试NaN的通常方法是查看它是否等于自身：

def isNaN(num):
    return num != num

math.isnan（）

或将数字与自身进行比较。NaN总是！=NaN，否则（例如，如果是数字），比较应成功。

这里有三种方法可以测试变量是否为“NaN”。

import pandas as pd
import numpy as np
import math

# For single variable all three libraries return single boolean
x1 = float("nan")

print(f"It's pd.isna: {pd.isna(x1)}")
print(f"It's np.isnan: {np.isnan(x1)}}")
print(f"It's math.isnan: {math.isnan(x1)}}")

输出

It's pd.isna: True
It's np.isnan: True
It's math.isnan: True

对于panda中的字符串，请使用pd.isnull：

if not pd.isnull(atext):
  for word in nltk.word_tokenize(atext):

NLTK的特征提取功能

def act_features(atext):
features = {}
if not pd.isnull(atext):
  for word in nltk.word_tokenize(atext):
    if word not in default_stopwords:
      features['cont({})'.format(word.lower())]=True
return features

使用math.isnan：

>>> import math
>>> x = float('nan')
>>> math.isnan(x)
True

似乎检查它是否等于自身（x！=x）是最快的。

import pandas as pd 
import numpy as np 
import math 

x = float('nan')

%timeit x != x
44.8 ns ± 0.152 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)

%timeit math.isnan(x)
94.2 ns ± 0.955 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)

%timeit pd.isna(x)
281 ns ± 5.48 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

%timeit np.isnan(x)
1.38 µs ± 15.7 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)