Python Truth Value Testing

What is Truth Value

We can use any object to test the truth value. By providing the condition in the if or while statement, the checking can be done.

Until a class method __bool__() returns False or __len__() method returns 0, we can consider the truth value of that object is True.

• The value of a constant is False, when it is False, or None.

• When a variable contains different values like 0, 0.0, Fraction(0, 1), Decimal(0), 0j, then it signifies the False Value.

• The empty sequence ??, [], (), {}, set(0), range(0), Truth value of these elements are False.

Truth Value of 1 and 0

The truth value 0 is equivalent to False and 1 is same as True. Let?s see the truth value i.e. the truth value of 1 is True ?

a = 1, then
bool(a) = True

Let?s see the opposite of the truth value i.e. the truth value of 0 is False ?

a = 0, then
bool(a) = False

Let us see another quick example. The truth value of 1 is True ?

a = 1

if(a==1)
   print("True")

The truth value of 0 is False ?

a = 0

if(a==0)
   print("False")

Python Truth Value Testing Example

Let us see a complete example ?

Example

<div class="execute"></div><div class="code-mirror  language-python" contenteditable="plaintext-only" spellcheck="false" style="outline: none; overflow-wrap: break-word; overflow-y: auto; white-space: pre-wrap;"><span class="token keyword">class</span> <span class="token class-name">A</span><span class="token punctuation">:</span>
<span class="token comment"># The class A has no __bool__ method, so default value of it is True</span>
	<span class="token keyword">def</span> <span class="token function">__init__</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
	    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'This is class A'</span><span class="token punctuation">)</span>

a_obj <span class="token operator">=</span> A<span class="token punctuation">(</span><span class="token punctuation">)</span>

<span class="token keyword">if</span> a_obj<span class="token punctuation">:</span>
	<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'It is True'</span><span class="token punctuation">)</span>
<span class="token keyword">else</span><span class="token punctuation">:</span>
	<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'It is False'</span><span class="token punctuation">)</span>

<span class="token keyword">class</span> <span class="token class-name">B</span><span class="token punctuation">:</span>
<span class="token comment"># The class B has __bool__ method, which is returning false value</span>
	<span class="token keyword">def</span> <span class="token function">__init__</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
		<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'This is class B'</span><span class="token punctuation">)</span>

	<span class="token keyword">def</span> <span class="token function">__bool__</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
		<span class="token keyword">return</span> <span class="token boolean">False</span>

b_obj <span class="token operator">=</span> B<span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token keyword">if</span> b_obj<span class="token punctuation">:</span>
	<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'It is True'</span><span class="token punctuation">)</span>
<span class="token keyword">else</span><span class="token punctuation">:</span>
	<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'It is False'</span><span class="token punctuation">)</span>

myList <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span>
<span class="token comment"># No element is available, so it returns False</span>
<span class="token keyword">if</span> myList<span class="token punctuation">:</span>
	<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'It has some elements'</span><span class="token punctuation">)</span>
<span class="token keyword">else</span><span class="token punctuation">:</span>
	<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'It has no elements'</span><span class="token punctuation">)</span>

mySet <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">,</span> <span class="token number">47</span><span class="token punctuation">,</span> <span class="token number">84</span><span class="token punctuation">,</span> <span class="token number">15</span><span class="token punctuation">)</span>
<span class="token comment"># Some elements are available, so it returns True</span>
<span class="token keyword">if</span> mySet<span class="token punctuation">:</span>
	<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'It has some elements'</span><span class="token punctuation">)</span>
<span class="token keyword">else</span><span class="token punctuation">:</span>
	<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">'It has no elements'</span><span class="token punctuation">)</span>
</div><div class="output-wrapper"><div class="console-close"></div><div class="code-output"></div></div>

Output

This is class A
It is True
This is class B
It is False
It has no elements
It has some elements