Is Naming Lambdas in Python Considered Pythonic?

Is Naming Lambdas Pythonic?

In Python, lambda expressions are designed to be anonymous functions. However, some developers find value in naming lambdas within functions for code reuse and specific functionality. However, this practice raises the question: is it compliant with Pythonic principles?

According to PEP8, the Python style guide, naming lambdas is discouraged. Instead, it recommends using def statements to define functions with specific names. This ensures clarity, simplifies tracebacks, and eliminates any benefits of using lambda expressions.

A lambda expression's defining characteristic is its anonymity. By naming it, you effectively remove that anonymity. Moreover, if the functionality is specific to the function in which it appears, defining a separate function may not be necessary. Consider using a nested function instead.

For example, in the given code snippet:

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

    # codecodecode
    
    indexed = indexer(array0, array1, indices)
    
    # codecodecode in which other arrays are created and require `indexer`
    
    return the_answer

Rather than naming the lambda expression indexer, it could be defined using a nested function:

def fcn_operating_on_arrays(array0, array1):
    def indexer(a0, a1, idx):
        return a0[idx] + a1[idx]

    # codecodecode
    
    indexed = indexer(array0, array1, indices)
    
    # codecodecode in which other arrays are created and require `indexer`
    
    return the_answer

By using a nested function, the functionality remains specific to the outer function, provides a named function, and adheres to Pythonic principles.

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