On Sun, 26 May 2019 at 00:37, Guido van Rossum <gu...@python.org> wrote: > > This looks great. > > I only have two nits with the text. > > First, why is the snapshot called a "dynamic snapshot"? What exactly is > dynamic about it?
The dynamic part comes in if you call locals() twice: because it returns the same mapping object every time, the second call to locals() will update the snapshot with the updated values of the local variables. To get a static snapshot that won't be implicitly updated by subsequent calls to locals() (or accesses to frame.f_locals, or implicit updates prior to trace function invocation) you have to do "locals().copy()". As others have noted, this isn't the behaviour we would choose if we were designing this API from scratch, but the current CPython behaviour has ~18 years of de facto standardisation behind it (as near as I can tell it has worked this way since nested scopes and fast locals were introduced in Python 2.1), so I'd be pretty hesitant about changing it at this point. In particular, I want to preserve the existing behaviour of Python 3 code that runs exec() and eval() at function scope, which means ensuring that locals(): 1. Continues to behave like a normal dict instance when passed to another API 2. Continues to leave the actual local variables of the calling frame alone > Second, you use the word "mapping" a lot. Would you mind changing that to > "mapping object" in most places? Especially in the phrase "each call to > ``locals()`` returns the *same* mapping". To me, without the word "object" > added, this *could* be interpreted as "a dict with the same key/value pairs" > (since "mapping" is also an abstract mathematical concept describing anything > that maps keys to values). That makes sense - I'll update the text. Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
