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Nitpicks in the new example
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README.md
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README.md
vendored
@ -1888,57 +1888,60 @@ tuple()
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1\.
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```py
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def func(k):
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if k == 3:
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return ["A string..."]
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def some_func(x):
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if x == 3:
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return ["wtf"]
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else:
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yield from range(k)
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yield from range(x)
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```
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**Output:**
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```py
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>>> list(func(3)) # expected: ["A string..."]
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>>> list(some_func(3))
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[]
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```
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The same behavior is true if we rewrite `yield from` as a for loop.
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Where did the `"wtf"` go? Is it due to some special effect of `yield from`? Let's validate that,
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2\.
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```py
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def func(k):
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if k == 3:
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return ["A string..."]
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def some_func(x):
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if x == 3:
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return ["wtf"]
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else:
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for j in range(k):
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yield j
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for i in range(x):
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yield i
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```
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**Output:**
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```py
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>>> list(func(3)) # expected: ["A string..."]
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>>> list(some_func(3))
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[]
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```
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Same result, that didn't work either.
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#### 💡 Explanation:
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Starting from Python 3.3+ it became possible to use return statement
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with values inside generators ([PEP380](https://www.python.org/dev/peps/pep-0380/)). The [official doc](https://www.python.org/dev/peps/pep-0380/#enhancements-to-stopiteration) says that "... `return expr` in a generator causes `StopIteration(expr)` to be raised upon exit from the generator."
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+ From Python 3.3 onwards, it became possible to use `return` statement with values inside generators (See [PEP380](https://www.python.org/dev/peps/pep-0380/)). The [official docs](https://www.python.org/dev/peps/pep-0380/#enhancements-to-stopiteration) say that,
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So, to get `["A string..."]` from the generator `func` we need to catch `StopIteration`, e.g.:
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> "... `return expr` in a generator causes `StopIteration(expr)` to be raised upon exit from the generator."
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```py
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try:
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next(func(3))
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except StopIteration as e:
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string = e.value
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```
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+ In case of `some_func(3)`, `StopIteration` is raised at the beginning because of `return` statement. The `StopIteration` exception is automatically catched inside the `list(...)` wrapper and the `for` loop. Therefore, the above two snippets result in an empty list.
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```py
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>>> string
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['A string...']
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```
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+ To get `["wtf"]` from the generator `some_func` we need to catch the `StopIteration` exception,
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```py
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try:
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next(some_func(3))
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except StopIteration as e:
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some_string = e.value
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```
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```py
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>>> some_string
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["wtf"]
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```
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Note that `list(...)` automatically catches `StopIteration`. In case of `func(3)` `StopIteration` raises at the beginning because of `return` statement. Therefore, `list(func(3))` results in an empty list.
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---
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