Python tutorial section 5.5 "It is an error to extract a value using a non-existent key."

[Dan-at-56]

Documentation

I am a beginner in Python and also on GitHub - my apologies in advance if this is a dumb suggestion or made inappropriately...

In the Python tutorial section 5.5 on dictionaries it says: "It is an error to extract a value using a non-existent key."
However, a quick test shows that an error is not generated. Rather, the value None is returned. Should the documentation be amended to that effect?

Python 3.12.2 (tags/v3.12.2:6abddd9, Feb  6 2024, 21:26:36) [MSC v.1937 64 bit (AMD64)] on win32
>>> my_dict = {'a': 1, 'b': 2, 'c': 3}
>>> value = my_dict.get('d')
>>> print(value)
None

Thanks,
Dan

Linked PRs

• gh-116488: Mention dict.get usage in data structures tutorial #139643
• [3.14] gh-116488: Mention dict.get in the data structures tutorial (GH-139643) #139655
• [3.13] gh-116488: Mention dict.get in the data structures tutorial (GH-139643) #139656

[Dan-at-56]

I note that I do get an error if attempting to extract the value using "my_dict['d'], so the documentation is correct if it's referring only to this method of extracting a value.

[terryjreedy]

The point of the .get method is to avoid the exception and possibly provide a non-default default.

@rhettinger or others. Should we add a qualifier here? How about mentioning dict.get and perhaps replace a redundant example with its use. Also, I notice that 11 methods are listed for lists and none for tuple, set, and dict. Add those for the rest?

[rhettinger]

How about mentioning dict.get and perhaps replace a redundant example with its use.

+1 The get() method is in common use and beginners would be benefit from being introduced early.

Also, I notice that 11 methods are listed for lists and none for tuple, set, and dict. Add those for the rest?

I don't think so. The tutorial is an introduction and its easy to drown a reader in details. For dicts and sets, it is better to focus on the core operations than to explore all the methods.

[sudoharshita16]

Hi @rhettinger @terryjreedy
I can look into this issue.

[terryjreedy]

At the end of the third paragraph of the dict doc, I propose replacing It is an error to extract a value using a non-existent key. with To avoid getting a KeyError when trying to extract a value for a possibly non-existent key, use the get method.

Then after

>>> tel['jack']
4098

insert

>>> tel.get('irv')
None

The 'irv' key is added later in the example.