python issue: using `is` relational operator with `numpy.all()`-CodePudding

When comparing numpy.all() of a boolean array of True values using the is operator I get an unexpected False as output. However I get the expected outcome (True) when using the == operator. What is the likely reason for this comparison failure?

A sample code is attached below.

In[2]: import sys
In[3]: print(sys.version)
3.9.5 

In[4]: import numpy as np
In[5]: np.__version__
'1.20.3'

In[6]: bool1 = True
In[7]: bool1 is True
True

In[8]: bool1 == True
True

In[9]: bool_arr = np.array([True, True, True, True])
In[10]: bool_arr.all()
True

In[11]: bool_arr.all() == True
True

In[12]: bool_arr.all() is True
False

As can be observed from the above code, in input 12, the expected outcome is True but the actual outcome is False.

I'm using pyenv in Ubuntu as the environment for python.

EDIT: as suggested in comments, this is not the best practice of using python. However, I'm interested to know the root cause for this failure.

CodePudding user response：

If you inspect the type of bool_arr.all(), the answer will be immediately apparent:

>>> bool_arr.all()
<class 'numpy.bool_'>

np.all returns an instance of a numpy bool_, which is a different class than python's built-in bool type. Instances of different types can not be the same object, which is what is is telling you.

The correct way to check truthiness is to let python wrap an expression in bool for you, e.g., in an if statement like if bool_arr.all():.