Python operator contains()

The operator.contains function in Python's operator module checks if an element is present in a container. It is equivalent to using the in operator but allows the membership test to be used as a function, which can be useful in functional programming and higher-order functions.

Table of Contents

1. Introduction
2. operator.contains Function Syntax
3. Examples
   • Basic Usage
   • Checking in Lists
   • Checking in Strings
   • Checking in Dictionaries
4. Real-World Use Case
5. Conclusion

Introduction

The operator.contains function checks if an element is present in a container (such as a list, string, or dictionary). It returns True if the element is found and False otherwise. This function is useful when you need to pass the membership test as a function to other functions or use it in functional programming contexts.

operator.contains Function Syntax

Here is how you use the operator.contains function:

import operator

result = operator.contains(container, element)

Parameters:

• container: The container to be searched (such as a list, string, or dictionary).
• element: The element to search for in the container.

Returns:

• True if the element is found in the container, False otherwise.

Examples

Basic Usage

Check if an element is present in a list using operator.contains.

Example

import operator

container = [1, 2, 3, 4, 5]
element = 3
result = operator.contains(container, element)
print(f"contains({container}, {element}) = {result}")

Output:

contains([1, 2, 3, 4, 5], 3) = True

Checking in Lists

Check if an element is present in a list.

Example

import operator

numbers = [10, 20, 30, 40, 50]
value = 25
result = operator.contains(numbers, value)
print(f"contains({numbers}, {value}) = {result}")

Output:

contains([10, 20, 30, 40, 50], 25) = False

Checking in Strings

Check if a substring is present in a string.

Example

import operator

string = "Hello, world!"
substring = "world"
result = operator.contains(string, substring)
print(f"contains({string}, '{substring}') = {result}")

Output:

contains(Hello, world!, 'world') = True

Checking in Dictionaries

Check if a key is present in a dictionary.

Example

import operator

dictionary = {"a": 1, "b": 2, "c": 3}
key = "b"
result = operator.contains(dictionary, key)
print(f"contains({dictionary}, '{key}') = {result}")

Output:

contains({'a': 1, 'b': 2, 'c': 3}, 'b') = True

Real-World Use Case

Filtering Data

In data processing, you might need to filter data based on the presence of elements in a container. The operator.contains function can be used in a functional programming style to achieve this.

Example

import operator

data = ["apple", "banana", "cherry", "date"]
filter_values = {"banana", "date"}

filtered_data = list(filter(lambda x: operator.contains(filter_values, x), data))
print(f"Filtered data: {filtered_data}")

Output:

Filtered data: ['banana', 'date']

Conclusion

The operator.contains function is used for performing membership tests in a functional programming context in Python. It provides a way to use the in operator as a function, which can be passed to other functions or used in higher-order functions. By understanding how to use operator.contains, you can write more flexible and readable code that leverages functional programming techniques.