Issue 31075: Collections - ChainMap - Documentation example wrong order line (original) (raw)

Issue31075

Created on 2017-07-29 12:24 by Marcos Soutullo, last changed 2022-04-11 14:58 by admin. This issue is now closed.

Messages (3)
msg299465 - (view)	Author: Marcos Soutullo (Marcos Soutullo)	Date: 2017-07-29 12:24
Hello, I have been taking a look into your ChainMap collections documentation (https://docs.python.org/3.6/library/collections.html?highlight=collections#collections.ChainMap), specifically the third code example on "8.3.1.1. ChainMap Examples and Recipes" that clearly describe and illustrate a use case for the ChainMap class. However, I found a very small code issue in regards to how the sample code (line 7) is presented to the reader. Please refer to the code compilation below: Line 7 >>> d['x'] # Get first key in the chain of contexts raise KeyError(key) KeyError: 'x' Line 8 >>> d['x'] d['x'] = 1 # Set value in current context The key named 'x' had not been initialised yet and of course, the compiler is complaining. It should be the other way around. Line 8 >>> d['x'] = 1 # Set value in current context Line 7 >>> d['x'] # Get first key in the chain of contexts Many thanks for the great work you do with Python, Marcos S.
msg299478 - (view)	Author: Raymond Hettinger (rhettinger) *	Date: 2017-07-29 17:03
-0 The code block was originally intended to just be a table of patterns, not meant to be executed sequentially. It followed the traditional presentation order (__getitem__, __setitem__, followed by __delitem__). If we do change this, then the subsequent "k in d" example should also be changed to "'x' in d" because k isn't defined.
msg299484 - (view)	Author: Raymond Hettinger (rhettinger) *	Date: 2017-07-29 19:18
> Many thanks for the great work you do with Python, Thanks for the kudos. Also, thanks for the close reading of the docs.