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Satwik 2019-12-20 23:39:10 +05:30
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@ -1,4 +1,4 @@
<p align="center"><img src="images/logo.png" alt=""></p>
<p align="center"><img src="/images/logo.png" alt=""></p>
<h1 align="center">What the f*ck Python! 🐍</h1>
<p align="center">An interesting collection of surprising snippets and lesser-known Python features.</p>
@ -338,7 +338,7 @@ Makes sense, right?
* All length 0 and length 1 strings are interned.
* Strings are interned at compile time (`'wtf'` will be interned but `''.join(['w', 't', 'f']` will not be interned)
* Strings that are not composed of ASCII letters, digits or underscores, are not interned. This explains why `'wtf!'` was not interned due to `!`. CPython implementation of this rule can be found [here](https://github.com/python/cpython/blob/3.6/Objects/codeobject.c#L19)
<img src="images/string-intern/string_intern.png" alt="">
![image](/images/string-intern/string_intern.png)
+ When `a` and `b` are set to `"wtf!"` in the same line, the Python interpreter creates a new object, then references the second variable at the same time. If you do it on separate lines, it doesn't "know" that there's already `wtf!` as an object (because `"wtf!"` is not implicitly interned as per the facts mentioned above). It's a compile-time optimization. This optimization doesn't apply to 3.7.x versions of CPython (check this [issue](https://github.com/satwikkansal/wtfpython/issues/100) for more discussion).
+ A compile unit in an interactive environment like IPython consists of a single statement, whereas it consists of the entire module in case of modules. `a, b = "wtf!", "wtf!"` is single statement, whereas `a = "wtf!"; b = "wtf!"` are two statements in a single line. This explains why the identities are different in `a = "wtf!"; b = "wtf!"`, and also explain why they are same when invoked in `some_file.py`
+ The abrupt change in the output of the fourth snippet is due to a [peephole optimization](https://en.wikipedia.org/wiki/Peephole_optimization) technique known as Constant folding. This means the expression `'a'*20` is replaced by `'aaaaaaaaaaaaaaaaaaaa'` during compilation to save a few clock cycles during runtime. Constant folding only occurs for strings having a length of less than 20. (Why? Imagine the size of `.pyc` file generated as a result of the expression `'a'*10**10`). [Here's](https://github.com/python/cpython/blob/3.6/Python/peephole.c#L288) the implementation source for the same.
@ -892,11 +892,11 @@ We didn't assign three `"X"`s, did we?
When we initialize `row` variable, this visualization explains what happens in the memory
![image](images/tic-tac-toe/after_row_initialized.png)
![image](/images/tic-tac-toe/after_row_initialized.png)
And when the `board` is initialized by multiplying the `row`, this is what happens inside the memory (each of the elements `board[0]`, `board[1]` and `board[2]` is a reference to the same list referred by `row`)
![image](images/tic-tac-toe/after_board_initialized.png)
![image](/images/tic-tac-toe/after_board_initialized.png)
We can avoid this scenario here by not using `row` variable to generate `board`. (Asked in [this](https://github.com/satwikkansal/wtfpython/issues/68) issue).
@ -3507,4 +3507,4 @@ If you like wtfpython, you can use these quick links to share it with your frien
## More content like this?
If you're interested in more content like this, you can share your email [here](https://satwikkansal.xyz/wtfpython-pdf/).
If you're interested in more content like this, you can share your email [here](https://satwikkansal.xyz/content-like-wtfpython/).