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Added new example: deep copy list #225
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Original file line number | Diff line number | Diff line change |
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@@ -59,6 +59,7 @@ So, here we go... | |
+ [▶ The disappearing variable from outer scope](#-the-disappearing-variable-from-outer-scope) | ||
+ [▶ The mysterious key type conversion](#-the-mysterious-key-type-conversion) | ||
+ [▶ Let's see if you can guess this?](#-lets-see-if-you-can-guess-this) | ||
+ [▶ Copy DEEP without deep copy](#-copy-deep-without-deep-copy) | ||
* [Section: Slippery Slopes](#section-slippery-slopes) | ||
+ [▶ Modifying a dictionary while iterating over it](#-modifying-a-dictionary-while-iterating-over-it) | ||
+ [▶ Stubborn `del` operation](#-stubborn-del-operation) | ||
|
@@ -1898,6 +1899,49 @@ a, b = a[b] = {}, 5 | |
True | ||
``` | ||
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--- | ||
### ▶ Copy DEEP without deep copy | ||
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```py | ||
>>> new_list = [1,2,4,5,6] | ||
>>> new_list_copy = new_list | ||
>>> new_list_copy.append(10) | ||
``` | ||
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**Output:** | ||
```py | ||
>>> new_list | ||
[1, 2, 4, 5, 6, 10] | ||
>>> new_list_copy | ||
[1, 2, 4, 5, 6, 10] | ||
``` | ||
***But....*** | ||
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```py | ||
>>> new_list = [1,2,4,5,6] | ||
>>> new_list_dcopy = new_list[:] | ||
>>> new_list_dcopy.append(20) | ||
``` | ||
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**Output:** | ||
```py | ||
>>> new_list | ||
[1, 2, 4, 5, 6] | ||
>>> new_list_dcopy | ||
[1, 2, 4, 5, 6, 20] | ||
``` | ||
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_What did just happen then?_ | ||
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#### 💡 Explanation: | ||
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In Python, we have concept of [deep copy](https://docs.python.org/3/library/copy.html) and [shallow copy](https://docs.python.org/3/library/copy.html). | ||
In the first example, `new_list` is the original list and `new_list_copy` is the shallow copy of the original list. As a result changes made to the copied list has reflected back to the original list. | ||
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The second example shows that `new_list_dcopy` is a deep copy of the original list `new_list`, where changes made in the deep copied list doesn't reflect back to the original list. | ||
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One can easily deep copy a list without using the *copy.deepcopy(new_list)* just by using `slicing` , where any changes made to the copied list won't reflect back to the original list. Trick!! | ||
Comment on lines
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+1943
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Actually, slicing a list using an empty |
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This isn't quite right,
new_list_copy
is not a copy ofnew_list
at all. It is simply a reference to it, a simple assignment in Python never creates a copy. You can compare the two lists withis
to test.