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Minor README fixups

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bwduncan 2021-10-29 20:52:07 +01:00 committed by GitHub
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README.md vendored
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@ -449,7 +449,7 @@ True
```py ```py
>>> a, b = 257, 257 >>> a, b = 257, 257
>> a is b >>> a is b
False False
``` ```
@ -917,7 +917,7 @@ array_4 = [400, 500, 600]
- In a [generator](https://wiki.python.org/moin/Generators) expression, the `in` clause is evaluated at declaration time, but the conditional clause is evaluated at runtime. - In a [generator](https://wiki.python.org/moin/Generators) expression, the `in` clause is evaluated at declaration time, but the conditional clause is evaluated at runtime.
- So before runtime, `array` is re-assigned to the list `[2, 8, 22]`, and since out of `1`, `8` and `15`, only the count of `8` is greater than `0`, the generator only yields `8`. - So before runtime, `array` is re-assigned to the list `[2, 8, 22]`, and since out of `1`, `8` and `15`, only the count of `8` is greater than `0`, the generator only yields `8`.
- The differences in the output of `g1` and `g2` in the second part is due the way variables `array_1` and `array_2` are re-assigned values. - The differences in the output of `g1` and `g2` in the second part is due the way variables `array_1` and `array_2` are re-assigned values.
- In the first case, `array_1` is binded to the new object `[1,2,3,4,5]` and since the `in` clause is evaluated at the declaration time it still refers to the old object `[1,2,3,4]` (which is not destroyed). - In the first case, `array_1` is bound to the new object `[1,2,3,4,5]` and since the `in` clause is evaluated at the declaration time it still refers to the old object `[1,2,3,4]` (which is not destroyed).
- In the second case, the slice assignment to `array_2` updates the same old object `[1,2,3,4]` to `[1,2,3,4,5]`. Hence both the `g2` and `array_2` still have reference to the same object (which has now been updated to `[1,2,3,4,5]`). - In the second case, the slice assignment to `array_2` updates the same old object `[1,2,3,4]` to `[1,2,3,4,5]`. Hence both the `g2` and `array_2` still have reference to the same object (which has now been updated to `[1,2,3,4,5]`).
- Okay, going by the logic discussed so far, shouldn't be the value of `list(gen)` in the third snippet be `[11, 21, 31, 12, 22, 32, 13, 23, 33]`? (because `array_3` and `array_4` are going to behave just like `array_1`). The reason why (only) `array_4` values got updated is explained in [PEP-289](https://www.python.org/dev/peps/pep-0289/#the-details) - Okay, going by the logic discussed so far, shouldn't be the value of `list(gen)` in the third snippet be `[11, 21, 31, 12, 22, 32, 13, 23, 33]`? (because `array_3` and `array_4` are going to behave just like `array_1`). The reason why (only) `array_4` values got updated is explained in [PEP-289](https://www.python.org/dev/peps/pep-0289/#the-details)
@ -1841,9 +1841,9 @@ NameError: name 'e' is not defined
**Output:** **Output:**
```py ```py
>>>f(x) >>> f(x)
UnboundLocalError: local variable 'x' referenced before assignment UnboundLocalError: local variable 'x' referenced before assignment
>>>f(y) >>> f(y)
UnboundLocalError: local variable 'x' referenced before assignment UnboundLocalError: local variable 'x' referenced before assignment
>>> x >>> x
5 5
@ -2753,7 +2753,7 @@ def similar_recursive_func(a):
* As for the fifth snippet, most methods that modify the items of sequence/mapping objects like `list.append`, `dict.update`, `list.sort`, etc. modify the objects in-place and return `None`. The rationale behind this is to improve performance by avoiding making a copy of the object if the operation can be done in-place (Referred from [here](https://docs.python.org/3/faq/design.html#why-doesn-t-list-sort-return-the-sorted-list)). * As for the fifth snippet, most methods that modify the items of sequence/mapping objects like `list.append`, `dict.update`, `list.sort`, etc. modify the objects in-place and return `None`. The rationale behind this is to improve performance by avoiding making a copy of the object if the operation can be done in-place (Referred from [here](https://docs.python.org/3/faq/design.html#why-doesn-t-list-sort-return-the-sorted-list)).
* Last one should be fairly obvious, mutable object (like `list`) can be altered in the function, and the reassignation of an immutable (`a -= 1`) is not an alteration of the value. * Last one should be fairly obvious, mutable object (like `list`) can be altered in the function, and the reassignment of an immutable (`a -= 1`) is not an alteration of the value.
* Being aware of these nitpicks can save you hours of debugging effort in the long run. * Being aware of these nitpicks can save you hours of debugging effort in the long run.