Using in vs. find() in Python

Overview

If you don’t need the index, but just want to test for inclusion, always use the in keyword instead of the find() method in Python.

Reasons for Different Functionality

Implementation and Short-circuiting

• The in keyword is a built-in operator in Python that works in conjunction with the __contains__ magic method of an object, while the find() method is a Python-level method implemented by certain types like strings.
• Both in and find() can stop the search as soon as they find the element or substring, which is a form of short-circuiting. This behavior can optimize the speed of these operations for specific use cases.
• The in operator only needs to return a boolean value indicating presence or absence, while the find() method returns the index of the first occurrence of the substring.
• For built-in types like sets and dictionaries, Python’s in operator can use a hash-based lookup, which can be faster than a linear search for certain cases.

Purpose

• The in operator is designed specifically to check for the presence of an element in a sequence, while the find() method is designed to search for a substring and return its index.
• Since the in operator only needs to return a boolean value, its implementation is focused on presence checking, while find() also provides the index of the found substring.

Conclusion

The choice between in and find() depends on the specific use case. The in operator is ideal for simple presence checks, while the find() method is suitable when you need to know the index of the substring.

In terms of performance, the in keyword will always be faster than the find() method.