Add new example

Closes https://github.com/satwikkansal/wtfPython/issues/9

README.md

@@ -1396,6 +1396,59 @@ tuple()
 
 ---
 
+### Let's see if you can guess this?
+
+Originally, suggested by @PiaFraus in [this](https://github.com/satwikkansal/wtfPython/issues/9) issue.
+
+**Output:**
+```py
+>>> a, b = a[b] = {}, 5
+>>> a
+{5: ({...}, 5)}
+```
+
+#### 💡 Explanation:
+
+* According to [Python language reference](https://docs.python.org/2/reference/simple_stmts.html#assignment-statements), assignment statements have the form
+  ```
+  (target_list "=")+ (expression_list | yield_expression)
+  ```
+  and
+  > 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.
+
+* 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`).
+
+* 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`.
+
+* `a` is now assigned to `{}` which is a mutable object.
+
+* 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`).
+
+* 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
+  ```py
+  >>> some_list = some_list[0] = [0]
+  >>> some_list
+  [[...]]
+  >>> some_list[0]
+  [[...]]
+  >>> some_list is some_list[0]
+  [[...]]
+  ```
+  Similar is the case in our example (`a[b][0]` is the same object as `a`)
+
+* So to sum it up, you can break the example down to
+  ```py
+  a, b = {}, 5
+  a[b] = a, b
+  ```
+  And the circular reference can be justified by the fact that `a[b][0]` is the same object as `a`
+  ```py
+  >>> a[b][0] is a
+  True
+  ```
+
+---
+
 ###  Minor Ones
 
 * `join()` is a string operation instead of list operation. (sort of counter-intuitive at first usage)