(Bad) practice of using this in Python


A technique found in a certain OSS.

bs = BookShelf('Introduction to XX', 'First time YY', 'ZZ I can't hear anymore')
bs.map_(lambda: print(this))


Introduction to XX
First time YY
ZZ I can't hear anymore

This that suddenly appeared. Where did it come from?


I was working on it before calling the callback.

class Book:
    def __init__(self, name):
        self._name = name
    def __str__(self):
        return self._name

class BookShelf:
    def __init__(self, *book_names):
        self._books = [*map(Book, book_names)]
    def map_(self, callback):
        for book in self._books:
            callback.__globals__['this'] = book
        del callback.__globals__['this']

It's not a big deal if you understand it, I was worried for a while because I doubted the extension of the interpreter and IDE.

Why I think it's a bad practice

I think it's Pythonic to pass it as an argument as follows.

class BookShelf:
    def __init__(self, *book_names):
        self._books = [*map(Book, book_names)]
    def map_(self, callback):
        for book in self._books:

bs = BookShelf('Introduction to XX', 'First time YY', 'ZZ I can't hear anymore')
bs.map_(lambda this: print(this))

I want to take good care of Zen of Python.

Explicit is better than implicit. It is better to clarify than to imply.

** Reference **: Qiita --The Zen of Python

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