Fear and suspicion of lambdas, was Re: Meta decorator with parameters, defined in explicit functions

Peter Otten __peter__ at web.de
Thu Jun 30 04:41:09 EDT 2016

Lawrence D’Oliveiro wrote:

> On Thursday, June 30, 2016 at 7:26:01 PM UTC+12, Peter Otten wrote:
>> foo = lambda <args>: <expr>
>> there is syntactic sugar in Python that allows you to write it as
>> def foo(<args>):
>>     return <expr>
>> with the nice side effects that it improves the readability of tracebacks
>> and allows you to provide a docstring.
> True, but then again the original had three lambdas, so one line would
> have to become at least 3×2 = 6 lines, more if you want docstrings.
>> def reduce(items, func=lambda x, y: x + y): ...
> There was a reason why “reduce” was removed from being a builtin function
> in Python 2.x, to being banished to functools in Python 3.

You do understand what an example is?

>> the alternative
>> def reduce(items, func=add): ...
>> looks more readable in my eyes even though somewhere ...
> Just use “sum” in this case.

Nah, the implementation is of course

def reduce(items, func=lambda x, y: x + y):
    >>> list(reduce([1,2,3]))
    [1, 3, 6]

    >>> list(reduce([42]))

    >>> reduce([])
    Traceback (most recent call last):
    TypeError: reduce() with empty sequence
    items = iter(items)
        first = next(items)
    except StopIteration:
        raise TypeError("reduce() with empty sequence")

    def _reduce(accu=first):
        for item in items:
            yield accu
            accu = func(accu, item)
        yield accu

    return _reduce()

Yes, I'm kidding...

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