Python numpy.ndarray与None的判定(错误判定/正确判定方法汇总)

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已于 2023-09-06 09:06:40 修改

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分类专栏： numpy python 文章标签： python numpy 开发语言

于 2023-08-31 14:33:59 首次发布

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本文探讨了在Python中使用numpy数组v与None值进行判断时的常见错误，以及正确的判定方法，强调了使用`isNone`检查法的重要性。

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样例假设：设一变量v，v可以是numpy.ndarray，也可以是None，做v为numpy.ndarry与None值的判定

v 为 numpy.ndarray

In [1]: import numpy as np

In [2]: v = np.zeros((2,2))

In [3]: print(type(v))
<class 'numpy.ndarray'>

In [4]: print(v)
[[0. 0.]
 [0. 0.]]

v 为 None

In [5]: v = None

In [6]: print(type(v))
<class 'NoneType'>

In [7]: print(v)
None

错误判定方法一：使用None == v进行判定

当v = None时通过

In [8]: v = None

In [9]: if None == v:
   ...:     print("判定通过")
   ...: else:
   ...:     print("判定通过")
判定通过

当v = np.zeros((2,2))报错

In [10]: v = np.zeros((2,2))

In [11]: if None == v:
    ...:     print("判定通过")
    ...: else:
    ...:     print("判定通过")
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-10-cb564f23b615> in <module>
----> 1 if None == v:
      2     print("判定通过")
      3 else:
      4     print("判定通过")
      5

ValueError: The truth value of an array with more than one element is ambiguous.
Use a.any() or a.all()

错误判定方法二：使用False == v.any()进行判定（来自错误判定方法一的提示）

当v = None时报错

In [12]: v = None

In [13]: if False == v.any():
    ...:     print("判定通过")
    ...: else:
    ...:     print("判定通过")
    ...: 
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-12-579411b4814e> in <module>
----> 1 if False == v.any():
      2     print("判定通过")
      3 else:
      4     print("判定通过")
      5

AttributeError: 'NoneType' object has no attribute 'any'

当v = np.zeros((2,2))通过

In [14]: v = np.zeros((2,2))

In [15]: if False == v.any():
    ...:     print("判定通过")
    ...: else:
    ...:     print("判定通过")
    ...:
判定通过

错误判定方法三：使用False == v.all()进行判定（来自错误判定方法一的提示）

当v = None时报错

In [16]: v = None

In [17]: if False == v.all():
    ...:     print("判定通过")
    ...: else:
    ...:     print("判定通过")
    ...: 
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-17-c879f04e8cf0> in <module>
----> 1 if False == v.all():
      2     print("判定通过")
      3 else:
      4     print("判定通过")
      5

AttributeError: 'NoneType' object has no attribute 'all'

当v = np.zeros((2,2))通过

In [18]: v = np.zeros((2,2))

In [19]: if False == v.all():
    ...:     print("判定通过")
    ...: else:
    ...:     print("判定通过")
    ...: 
判定通过

错误判定方法四：使用v或not v进行判定（以not v为例，两者出错一致）

当v = None通过

In [20]: v = None

In [21]: if not v:
    ...:     print("判定通过")
    ...: else:
    ...:     print("判定通过")
    ...: 
判定通过

当v = np.zeros((2,2))报错

In [22]: v = np.zeros((2,2))

In [23]: if not v:
    ...:     print("判定通过")
    ...: else:
    ...:     print("判定通过")
    ...: 
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-23-0396573717f2> in <module>
----> 1 if not v:
      2     print("判定通过")
      3 else:
      4     print("判定通过")
      5

ValueError: The truth value of an array with more than one element is ambiguous.
Use a.any() or a.all()

正确判定方法：使用v is None判定

当v = None通过

In [24]: v = None

In [25]: if v is None:
    ...:     print("判定通过")
    ...: else:
    ...:     print("判定通过")
    ...: 
判定通过

当v = np.zeros((2,2))通过

In [26]: v = np.zeros((2,2))

In [27]: if v is None:
    ...:     print("判定通过")
    ...: else:
    ...:     print("判定通过")
    ...: 
判定通过