6 ms·

You can put an extra 'level' in, to make both options return the same 0,1...9 def loop(): for number in range(10): def outer(n):

You can put an extra 'level' in, to make both options return the same 0,1...9 def loop(): for number in range(10): def outer(n): def inner(): return n return inner yield outer(number) Is there a neater way?

nbadg 2y ago
Yes. The usual way to do this is to bind them as defaults to an argument, for example: def loop(): for number in range(10): def func_w_closure(_num=number): return _num yield func_w_closure This works because default arguments in python are evaluated exactly once, at function definition time. So it's a way of effectively copying the ``number`` out of the closure[1] and into the function definition. [1] side note, closures in python are always late-binding, which is what causes the behavior in OP
- NwtnsMthd 2y ago
  Does this work for user defined classes (objects) as well?
  - Jtsummers 2y ago
    Yes, and by the same mechanism and for the same reason.
- amluto 2y ago
  I’ve never thought that leaking this type of implementation detail into the return value (and return type!) was a nice solution. I like the double closure better, and one can shorten it a bit with a lambda. For those who prefer a functional style, functools.partial can also solve this problem. (I use Python, and I like a lot of things about Python, but I don’t like its scoping rules at all, nor do I like the way that Python’s closures work. I would use a double lambda.)
- deleted 2y ago
  [deleted]
oulipo 2y ago
I would have just done something like ``` def loop(): for number in range(10): fixed_number = number def inner(): return fixed_number yield inner ```
- Jtsummers 2y ago
  Correctly formatted (two spaces preceding each line, one blank line before the first code line, no extra lines needed between code lines): def loop(): for number in range(10): fixed_number = number def inner(): return fixed_number yield inner The output: eagerly = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] lazily = [9, 9, 9, 9, 9, 9, 9, 9, 9, 9] It doesn't work because of the way Python's variables are scoped. Your fixed_number variable is still shared across all instances of inner. Python doesn't have any sort of block scoping like you seem to think it has.

nbadg 2y ago

Yes. The usual way to do this is to bind them as defaults to an argument, for example: def loop(): for number in range(10): def func_w_closure(_num=number): return _num yield func_w_closure This works because default arguments in python are evaluated exactly once, at function definition time. So it's a way of effectively copying the ``number`` out of the closure[1] and into the function definition. [1] side note, closures in python are always late-binding, which is what causes the behavior in OP

NwtnsMthd 2y ago
Does this work for user defined classes (objects) as well?
- Jtsummers 2y ago
  Yes, and by the same mechanism and for the same reason.
amluto 2y ago
I’ve never thought that leaking this type of implementation detail into the return value (and return type!) was a nice solution. I like the double closure better, and one can shorten it a bit with a lambda. For those who prefer a functional style, functools.partial can also solve this problem. (I use Python, and I like a lot of things about Python, but I don’t like its scoping rules at all, nor do I like the way that Python’s closures work. I would use a double lambda.)
deleted 2y ago
[deleted]

oulipo 2y ago

I would have just done something like ``` def loop(): for number in range(10): fixed_number = number def inner(): return fixed_number yield inner ```

Jtsummers 2y ago
Correctly formatted (two spaces preceding each line, one blank line before the first code line, no extra lines needed between code lines): def loop(): for number in range(10): fixed_number = number def inner(): return fixed_number yield inner The output: eagerly = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] lazily = [9, 9, 9, 9, 9, 9, 9, 9, 9, 9] It doesn't work because of the way Python's variables are scoped. Your fixed_number variable is still shared across all instances of inner. Python doesn't have any sort of block scoping like you seem to think it has.