mirror of
https://github.com/satwikkansal/wtfpython.git
synced 2024-09-11 20:17:08 +03:00
Add new example: The stubborn del operator
Closes https://github.com/satwikkansal/wtfpython/issues/26
This commit is contained in:
parent
e94cbea6bc
commit
f1c2b68d32
51
README.md
vendored
51
README.md
vendored
@ -103,8 +103,10 @@ So, here ya go...
|
|||||||
- [💡 Explanation:](#-explanation-28)
|
- [💡 Explanation:](#-explanation-28)
|
||||||
- [Implicity key type conversion](#implicity-key-type-conversion)
|
- [Implicity key type conversion](#implicity-key-type-conversion)
|
||||||
- [💡 Explanation:](#-explanation-29)
|
- [💡 Explanation:](#-explanation-29)
|
||||||
- [Let's see if you can guess this?](#lets-see-if-you-can-guess-this)
|
- [Stubborn `del` operator](#stubborn-del-operator)
|
||||||
- [💡 Explanation:](#-explanation-30)
|
- [💡 Explanation:](#-explanation-30)
|
||||||
|
- [Let's see if you can guess this?](#lets-see-if-you-can-guess-this)
|
||||||
|
- [💡 Explanation:](#-explanation-31)
|
||||||
- [Minor Ones](#minor-ones)
|
- [Minor Ones](#minor-ones)
|
||||||
- [TODO: Hell of an example!](#todo-hell-of-an-example)
|
- [TODO: Hell of an example!](#todo-hell-of-an-example)
|
||||||
- [Contributing](#contributing)
|
- [Contributing](#contributing)
|
||||||
@ -1931,6 +1933,53 @@ str
|
|||||||
(__main__.SomeClass, str)
|
(__main__.SomeClass, str)
|
||||||
```
|
```
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
### Stubborn `del` operator
|
||||||
|
|
||||||
|
Suggested by @tukkek in [this](https://github.com/satwikkansal/wtfpython/issues/26) issue.
|
||||||
|
|
||||||
|
```py
|
||||||
|
class SomeClass:
|
||||||
|
def __del__(self):
|
||||||
|
print("Deleted!")
|
||||||
|
```
|
||||||
|
|
||||||
|
**Output:**
|
||||||
|
1\.
|
||||||
|
```py
|
||||||
|
>>> x = SomeClass()
|
||||||
|
>>> y = x
|
||||||
|
>>> del x # this should print "Deleted!"
|
||||||
|
>>> del y
|
||||||
|
Deleted!
|
||||||
|
```
|
||||||
|
|
||||||
|
Phew, deleted at last. You might have guessed what saved from `__del__` being called in our first attempt to delete `x`. Let's add more twist ro the example.
|
||||||
|
|
||||||
|
2\.
|
||||||
|
```py
|
||||||
|
>>> x = SomeClass()
|
||||||
|
>>> y = x
|
||||||
|
>>> del x
|
||||||
|
>>> y # check if y exists
|
||||||
|
<__main__.SomeClass instance at 0x7f98a1a67fc8>
|
||||||
|
>>> del y # Like previously, this should print "Deleted!"
|
||||||
|
>>> globals() # oh, it didn't. Let's check all our global variables and confirm
|
||||||
|
Deleted!
|
||||||
|
{'__builtins__': <module '__builtin__' (built-in)>, 'SomeClass': <class __main__.SomeClass at 0x7f98a1a5f668>, '__package__': None, '__name__': '__main__', '__doc__': None}
|
||||||
|
```
|
||||||
|
|
||||||
|
Okay, now it's deleted :confused:
|
||||||
|
|
||||||
|
#### 💡 Explanation:
|
||||||
|
+ `del x` doesn’t directly call `x.__del__()`.
|
||||||
|
+ Whenever `del x` is encountered, Python decrements the reference count for `x` by one, and `x.__del__()` when x’s reference count reaches zero.
|
||||||
|
+ In the second output snippet, `y.__del__()` was not called because the previous statement (`>>> y`) in the interactive interpreter created another reference to the same object, thus preventing the reference count to reach zero when `del y` was encountered.
|
||||||
|
+ Calling `globals` caused the existing reference to be destroyed and hence we can see "Deleted!" being printed (finally!).
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
### Let's see if you can guess this?
|
### Let's see if you can guess this?
|
||||||
|
|
||||||
Suggested by @PiaFraus in [this](https://github.com/satwikkansal/wtfPython/issues/9) issue.
|
Suggested by @PiaFraus in [this](https://github.com/satwikkansal/wtfPython/issues/9) issue.
|
||||||
|
Loading…
Reference in New Issue
Block a user