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By the way, speaking of sum, I find it a bit strange that Python allows 'hello' + 'world' but not sum(['hello', 'world']) Intuitively I would have e

By the way, speaking of sum, I find it a bit strange that Python allows 'hello' + 'world' but not sum(['hello', 'world']) Intuitively I would have expected the latter to be possible given the former but I guess it comes down to how the + operator and the sum function are implemented in Python, such that counter to my expectation sum is not a function that "applies the + operator" to it's arguments. The notion that this is how it should work stems from my impression that "sum" belongs to the same family as do "map", "reduce" and "apply" -- that these are somehow "functional" in nature in the sense that is observed in the Lisp family of languages.

blixt 9y ago
I guess sum was only implemented to support numeric values. However you can easily roll your own: >>> def add(it): ... return reduce(lambda x, y: x + y, it) ... >>> add(['hello ', 'world']) 'hello world' >>> add(x for x in xrange(10)) 45 Edit: almost forgot a possibly even more Pythonic way: >>> import operator >>> def add(it): ... return reduce(operator.add, it)
- chicago_wade 9y ago
  >>> import operator >>> def add(it): ... return reduce(operator.add, it) Ooh, I like this one. Thanks!
  - blixt 9y ago
    Looping back to why sum doesn't work with strings, it looks like they implemented it like this: >>> def sum(it): ... return reduce(operator.add, it, 0) Basically the first value is always added to 0. This has one important difference which can be a valid compromise if you expect to almost always sum numbers. If you try to call add([]) without the initial 0, you'll get an error because there's no way to know what the zero value is. In a typed language you could use type inference and use the inferred type's zero value (if the language has such a concept for all types like for example Go does). In Python I guess you could fall back to None, but then you'd have code that doesn't behave consistently for all inputs.
kazinator 9y ago
The notion that that is how it work probably stems from you not having flunked computer science.

blixt 9y ago

I guess sum was only implemented to support numeric values. However you can easily roll your own: >>> def add(it): ... return reduce(lambda x, y: x + y, it) ... >>> add(['hello ', 'world']) 'hello world' >>> add(x for x in xrange(10)) 45 Edit: almost forgot a possibly even more Pythonic way: >>> import operator >>> def add(it): ... return reduce(operator.add, it)

chicago_wade 9y ago
>>> import operator >>> def add(it): ... return reduce(operator.add, it) Ooh, I like this one. Thanks!
- blixt 9y ago
  Looping back to why sum doesn't work with strings, it looks like they implemented it like this: >>> def sum(it): ... return reduce(operator.add, it, 0) Basically the first value is always added to 0. This has one important difference which can be a valid compromise if you expect to almost always sum numbers. If you try to call add([]) without the initial 0, you'll get an error because there's no way to know what the zero value is. In a typed language you could use type inference and use the inferred type's zero value (if the language has such a concept for all types like for example Go does). In Python I guess you could fall back to None, but then you'd have code that doesn't behave consistently for all inputs.

kazinator 9y ago

The notion that that is how it work probably stems from you not having flunked computer science.