Understanding "Does Not Equal" (`!=`) in Python

Key Takeaways

1. != compares values for inequality in Python.
2. It internally relies on the __ne__() or negated __eq__() method.
3. != checks value inequality, not object identity.

In Python, comparing values is a fundamental operation, and one of the most commonly used comparisons is checking whether two values are not equal. This operation is essential in decision-making, loops, and filtering logic throughout Python programs.

This article explains how Python represents "does not equal," how it works, and some common use cases and pitfalls.

---

The Syntax: !=

In Python, the "does not equal" operator is written as !=.

a = 5
b = 3

if a != b:
    print("a and b are not equal")

In this example, Python compares the values of a and b. Since 5 is not equal to 3, the condition evaluates to True, and the message is printed.

---

Behind the Scenes

The != operator checks inequality by internally calling the special method __ne__(). If __ne__() is not explicitly defined for a class, Python falls back on __eq__() and negates the result.

Here's a simple demonstration:

class AlwaysEqual:
    def __eq__(self, other):
        return True

obj = AlwaysEqual()

print(obj != 42)  # Output: False

Even though obj != 42 looks like a comparison for inequality, Python sees that obj.__ne__ is not defined and instead uses not obj.__eq__(42), which becomes not True, resulting in False.

---

Common Use Cases

1. Conditionals:

if user_input != "quit":
    continue_program()

2. Loop filters:

for item in items:
    if item != "skip":
        process(item)

3. Assertions in testing:

assert result != expected_error

---

!= vs is not

Python also provides is not, but it's different from !=.

• != checks value inequality
• is not checks object identity inequality

a = [1, 2]
b = [1, 2]

print(a != b)     # False — values are equal
print(a is not b) # True  — different objects in memory

This distinction is important when comparing custom objects or mutable types like lists and dictionaries.

---

Conclusion

The != operator in Python is a straightforward and powerful tool for comparing values. Understanding how it works—especially in relation to __eq__ and object identity—helps avoid subtle bugs and write more effective, expressive code.

When writing Python, remember:

• Use != to compare values for inequality.
• Be cautious when overriding equality methods in custom classes.
• Don’t confuse != with is not.

By mastering these distinctions, you'll be better equipped to write clean, logical conditionals and comparisons in Python.

FAQs

What's the difference between != and is not in Python?

!= compares values; is not checks whether two variables point to different objects in memory.

What happens if I don’t define __ne__() in a custom class?

Python uses not __eq__() as a fallback for !=.

Can != be used with all data types?

Yes, as long as the data types support equality comparison, != works with them.

We are Leapcell, your top choice for hosting Python projects.

Leapcell is the Next-Gen Serverless Platform for Web Hosting, Async Tasks, and Redis:

Multi-Language Support

• Develop with Node.js, Python, Go, or Rust.

Deploy unlimited projects for free

• pay only for usage — no requests, no charges.

Unbeatable Cost Efficiency

• Pay-as-you-go with no idle charges.
• Example: $25 supports 6.94M requests at a 60ms average response time.

Streamlined Developer Experience

• Intuitive UI for effortless setup.
• Fully automated CI/CD pipelines and GitOps integration.
• Real-time metrics and logging for actionable insights.

Effortless Scalability and High Performance

• Auto-scaling to handle high concurrency with ease.
• Zero operational overhead — just focus on building.

Explore more in the Documentation!

Follow us on X: @LeapcellHQ