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Add new example
Closes https://github.com/satwikkansal/wtfPython/issues/9
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README.md
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README.md
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@ -1396,6 +1396,59 @@ tuple()
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---
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### Let's see if you can guess this?
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Originally, suggested by @PiaFraus in [this](https://github.com/satwikkansal/wtfPython/issues/9) issue.
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**Output:**
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```py
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>>> a, b = a[b] = {}, 5
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>>> a
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{5: ({...}, 5)}
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```
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#### 💡 Explanation:
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* According to [Python language reference](https://docs.python.org/2/reference/simple_stmts.html#assignment-statements), assignment statements have the form
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```
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(target_list "=")+ (expression_list | yield_expression)
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```
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and
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> An assignment statement evaluates the expression list (remember that this can be a single expression or a comma-separated list, the latter yielding a tuple) and assigns the single resulting object to each of the target lists, from left to right.
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* The `+` in `(target_list "=")+` means there can be **one or more** target lists. In this case, target lists are `a, b` and `a[b]` (note the expression list is exactly one, which in our case is `{}, 5`).
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* After the expression list is evaluated, it's value is unpacked to the target lists from **left to right**. So, in our case, first the `{}, 5` tuple is unpacked to `a, b` and we now have `a = {}` and `b = 5`.
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* `a` is now assigned to `{}` which is a mutable object.
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* The second target list is `a[b]` (you may expect this to throw an error because both `a` and `b` have not been defined in the statements before. But remember, we just assigned `a` to `{}` and `b` to `5`).
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* Now, we are setting the key `5` in the dictionary to the tuple `({}, 5)` creating a circular reference (the `{...}` in the output refers to the same object that `a` is already referencing). Another simpler example of circular reference could be
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```py
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>>> some_list = some_list[0] = [0]
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>>> some_list
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[[...]]
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>>> some_list[0]
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[[...]]
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>>> some_list is some_list[0]
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[[...]]
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```
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Similar is the case in our example (`a[b][0]` is the same object as `a`)
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* So to sum it up, you can break the example down to
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```py
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a, b = {}, 5
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a[b] = a, b
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```
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And the circular reference can be justified by the fact that `a[b][0]` is the same object as `a`
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```py
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>>> a[b][0] is a
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True
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```
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---
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### Minor Ones
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* `join()` is a string operation instead of list operation. (sort of counter-intuitive at first usage)
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