diff --git a/README.md b/README.md index 974359a..67957cc 100644 --- a/README.md +++ b/README.md @@ -1,4 +1,4 @@ -

+

What the f*ck Python! 🐍

An interesting collection of surprising snippets and lesser-known Python features.

@@ -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) - + ![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/).