To Name or Not to Name: When Should You Assign Names to Lambdas in Python?

Should You Name Lambdas in Python?

Lambda expressions provide a concise and convenient way to define anonymous functions in Python. However, it is often tempting to assign names to lambdas within functions for code reuse and specific functionality.

Critique of Naming Lambdas

While this practice may seem convenient, it is generally considered non-Pythonic and goes against the recommendation of PEP8. As PEP8 states:

"Always use a def statement instead of an assignment statement that binds a lambda expression directly to an identifier."

The rationale behind this recommendation is that defining a lambda as a function:

• Provides a clear and explicit name: Unlike named lambdas, def statements explicitly associate the function with a meaningful identifier.
• Helps with traceback and string representations: Named functions display their specific name in error messages and string representations, providing better readability.
• Eliminates the primary benefit of lambdas: The ability to embed anonymous functions within larger expressions is redundant when you assign a variable to a lambda.

Example

Consider the example function provided in the question:

def fcn_operating_on_arrays(array0, array1):
    indexer = lambda a0, a1, idx: a0[idx] + a1[idx]
    
    # ...
    indexed = indexer(array0, array1, indices)
    # ...

Instead of using a named lambda, it is more Pythonic to define a separate, explicitly named function:

def index_array(a0, a1, idx):
    return a0[idx] + a1[idx]

def fcn_operating_on_arrays(array0, array1):
    
    # ...
    indexed = index_array(array0, array1, indices)
    # ...

Conclusion

While assigning names to lambdas may seem useful in certain situations, it is not recommended. Instead, follow the Pythonic principle of using explicit function definitions to maintain clarity, readability, and adherence to best practices.

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