mirror of
https://github.com/satwikkansal/wtfpython.git
synced 2024-09-11 20:17:08 +03:00
Merge examples
This commit is contained in:
parent
70fe61737b
commit
9608b2fcfc
34
README.md
vendored
34
README.md
vendored
@ -367,6 +367,7 @@ for i, some_dict[i] in enumerate(some_string):
|
||||
|
||||
### ▶ Evaluation time discrepancy
|
||||
|
||||
1\.
|
||||
```py
|
||||
array = [1, 8, 15]
|
||||
g = (x for x in array if array.count(x) > 0)
|
||||
@ -379,28 +380,21 @@ array = [2, 8, 22]
|
||||
[8]
|
||||
```
|
||||
|
||||
#### 💡 Explanation
|
||||
|
||||
- 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`.
|
||||
|
||||
---
|
||||
|
||||
### ▶ Generator with Slice Assignment
|
||||
2\.
|
||||
|
||||
```py
|
||||
iter1 = [1,2,3,4]
|
||||
g1 = (x for x in iter1)
|
||||
iter1 = [1,2,3,4,5]
|
||||
array_1 = [1,2,3,4]
|
||||
g1 = (x for x in array_1)
|
||||
array_1 = [1,2,3,4,5]
|
||||
|
||||
iter2 = [1,2,3,4]
|
||||
g2 = (x for x in iter2)
|
||||
iter2[:] = [1,2,3,4,5]
|
||||
array_2 = [1,2,3,4]
|
||||
g2 = (x for x in array_2)
|
||||
array_2[:] = [1,2,3,4,5]
|
||||
```
|
||||
|
||||
**Output:**
|
||||
```py
|
||||
>>>print(list(g1))
|
||||
>>> print(list(g1))
|
||||
[1,2,3,4]
|
||||
|
||||
>>> print(list(g2))
|
||||
@ -409,11 +403,11 @@ iter2[:] = [1,2,3,4,5]
|
||||
|
||||
#### 💡 Explanation
|
||||
|
||||
- In the first expression `g1` yields the elements of original list `iter1`(instead of updated one). Since the `in`
|
||||
clause is evaluated at the time of generator declaration, hence generator expression `g1` still have reference of original list
|
||||
`iter1`
|
||||
|
||||
- In the second example, list `iter1` is updated using slice assignment. Slice assignment, in contrast to normal assignment(which creates a new list), updates the same list. We can view this as the slice of list being replace by the iterable on right hand side of equality. Hence, the generator `g2` yields updated `iter2` elements.
|
||||
- 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`.
|
||||
- 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 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]`).
|
||||
|
||||
---
|
||||
|
||||
|
Loading…
Reference in New Issue
Block a user