Why Does \'1 in \'11\' == True\' Return a TypeError in Python?

Understanding Operator Precedence in Python: 'in' vs. Comparison

In Python, determining the order of operations can be crucial for evaluating expressions correctly. The precedence of operators specifies their priority, with higher-precedence operators being evaluated first.

Consider the following expressions:

<code class="python">'1' in '11'
('1' in '11') == True</code>

Both expressions evaluate to True, indicating that the 'in' operator has a lower precedence than the comparison operator '=='. However, placing parentheses around the 'in' expression alters the evaluation order:

<code class="python">'1' in ('11' == True)</code>

This expression raises a TypeError, indicating that something is not quite right. To understand why, let's examine Python's operator precedence.

According to the Python documentation, 'in' and '==' have equal precedence. Therefore, Python evaluates them from left to right. In this case, Python first evaluates '1' in '11', which results in True. However, the '== True' part is then evaluated as a Boolean expression, leading to the TypeError since a Boolean value cannot be iterated over.

To resolve this, you can leverage chaining. Chaining allows multiple operators with the same precedence to be grouped together and evaluated from left to right. By adding parentheses as follows, you can force the 'in' operator to be evaluated first:

<code class="python">'1' in '11' == True</code>

This expression evaluates to False, which aligns with your expectation. The parentheses ensure that the 'in' operator is evaluated first, resulting in True. This is then compared to True in the '==' expression, yielding False.

The above is the detailed content of Why Does \'1 in \'11\' == True\' Return a TypeError in Python?. For more information, please follow other related articles on the PHP Chinese website!