Reserved word pair used in lambda tutorial without being noted as a reserved word

[ChasBelov]

BPO	40641
Nosy	@mdickinson, @ChasBelov

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2020-05-16.10:05:13.643>
created_at = <Date 2020-05-16.06:57:50.222>
labels = ['3.7', 'invalid', 'docs']
title = 'Reserved word pair used in lambda tutorial without being noted as a reserved word'
updated_at = <Date 2020-05-16.10:05:13.642>
user = 'https://github.com/ChasBelov'

bugs.python.org fields:

activity = <Date 2020-05-16.10:05:13.642>
actor = 'mark.dickinson'
assignee = 'docs@python'
closed = True
closed_date = <Date 2020-05-16.10:05:13.643>
closer = 'mark.dickinson'
components = ['Documentation']
creation = <Date 2020-05-16.06:57:50.222>
creator = 'Chas Belov'
dependencies = []
files = []
hgrepos = []
issue_num = 40641
keywords = []
message_count = 2.0
messages = ['369017', '369020']
nosy_count = 3.0
nosy_names = ['mark.dickinson', 'docs@python', 'Chas Belov']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue40641'
versions = ['Python 3.7']

[ChasBelov]

In the tutorial for lambda expressions at https://docs.python.org/3.7/tutorial/controlflow.html#lambda-expressions the reserved word pair is introduced without noting that it is a reserved word. In the example given, I wasn't sure whether pair was a reserved word or whether the interpreter was parsing the plural "pairs" which is presumable an arbitrary name.

Actual content:

The above example uses a lambda expression to return a function. Another use is to pass a small function as an argument:

>>> pairs = [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]
>>> pairs.sort(key=lambda pair: pair[1])
>>> pairs
[(4, 'four'), (1, 'one'), (3, 'three'), (2, 'two')]

Candidate expected content:

The above example uses a lambda expression to return a function. Another use is to pass a small function as an argument, for example, the reserved word pair to designate the position in a tuple pair:

>>> items = [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]
>>> items.sort(key=lambda pair: pair[1])
>>> items
[(4, 'four'), (1, 'one'), (3, 'three'), (2, 'two')]

[mdickinson]

pair isn't a reserved word here; it's just the formal parameter name. Think of the lambda here as being equivalent to a function

    def second(pair):
        return pair[1]

You can replace the word "pair" here with any other valid Python identifier, and it'll still work the same way.