Python naming convention - namedtuples

Question

I am new to Python and I have been reading both the online documentation and (trying) to follow PEP 0008 to have a good Python code style. I am curious about the code segment I found in the official Python docs while studying about the re library:

import collections

Token = collections.namedtuple('Token', ['typ', 'value', 'line', 'column'])

I cannot understand why the Token variable is named with a first letter capitalised; I have read through the PEP 0008 and there is no reference for it for what I have seen. Should it not be token instead or TOKEN if it was a constant (which for all I know it is not)?

Because it's a class - `namedtuple` is a class factory. – jonrsharpe Apr 02 '16 at 08:35 — jonrsharpe, Apr 02 '16 at 08:35

Yannis · Accepted Answer · 2016-04-02T08:51:44.390

16

In the code-segment you provided, Token is a named tuple, definitely not a constant. It does not follow other variable names naming style only to put emphasis on the fact that it is a class factory function. No warning will occur from an PEP 0008 style checker (like PyCharm for example) if you write it as token but I think it is not good practice since this way it does not distinguish it as a class factory name.

So, namedtuples fall under the Class names in PEP 0008. Too bad is not stated more explicitly. Besides the example you mentioned for writing a tokenizer, this can also be seen in the collections.namedtuple docs examples:

Point = namedtuple('Point', ['x', 'y'])
Point3D = namedtuple('Point3D', Point._fields + ('z',))
Book = namedtuple('Book', ['id', 'title', 'authors'])

edited Apr 02 '16 at 08:51

answered Apr 02 '16 at 08:43

Yannis

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Anti Haapala's answer beat me to it. Great answer. – Yannis Apr 02 '16 at 08:44
Well your answer is better :d – Antti Haapala -- Слава Україні Apr 02 '16 at 08:47
@Yannis, worth including info from Class names link that Class names should normally use the CapWords convention, consequently named tuples – boardtc Oct 12 '19 at 22:10

score 8 · Answer 2 · edited Jun 20 '20 at 09:12

The key here is collections.namedtuple. As the documentation says,

collections.namedtuple(typename, field_names, verbose=False, rename=False)

Returns a new tuple subclass named typename. The new subclass is used to create tuple-like objects that have fields accessible by attribute lookup as well as being indexable and iterable. Instances of the subclass also have a helpful docstring (with typename and field_names) and a helpful __repr__() method which lists the tuple contents in a name=value format.

There is no PEP 8 violation; Token is an user-defined class and its name is capitalized as it should.

Python naming convention - namedtuples

2 Answers2