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New example: Lossy zip of iterators
Resolves https://github.com/satwikkansal/wtfpython/issues/121
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README.md
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README.md
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@ -1253,6 +1253,55 @@ I've lost faith in truth!
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---
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### ▶ Lossy zip of iterators
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```py
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>>> numbers = list(range(7))
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>>> numbers
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[0, 1, 2, 3, 4, 5, 6]
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>>> first_three, remaining = numbers[:3], numbers[3:]
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>>> first_three, remaining
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([0, 1, 2], [3, 4, 5, 6])
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>>> numbers_iter = iter(numbers)
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>>> list(zip(numbers_iter, first_three))
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[(0, 0), (1, 1), (2, 2)]
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# so far so good, let's zip the remaining
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>>> list(zip(numbers_iter, remaining))
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[(4, 3), (5, 4), (6, 5)]
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```
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Where did element `3` go from the `numbers` list?
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#### 💡 Explanation:
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- From Python [docs](https://docs.python.org/3.3/library/functions.html#zip), here's an approximate implementation of zip function,
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```py
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def zip(*iterables):
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sentinel = object()
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iterators = [iter(it) for it in iterables]
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while iterators:
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result = []
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for it in iterators:
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elem = next(it, sentinel)
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if elem is sentinel:
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return
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result.append(elem)
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yield tuple(result)
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```
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- So the function takes in arbitrary number of itreable objects, adds each of their items to the `result` list by calling the `next` function on them, and stops whenever any of the iterable is exhausted.
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- The caveat here is when any iterable is exhausted, the existing elements in the `result` list are discarded. That's what happened with `3` in the `numbers_iter`.
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- The correct way to do the above using `zip` would be,
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```py
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>>> numbers = list(range(7))
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>>> numbers_iter = iter(numbers)
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>>> list(zip(first_three, numbers_iter))
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[(0, 0), (1, 1), (2, 2)]
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>>> list(zip(remaining, numbers_iter))
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[(3, 3), (4, 4), (5, 5), (6, 6)]
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```
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The first argument of zip should be the one with fewest elements.
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---
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### ▶ From filled to None in one instruction...
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```py
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