builtins.True exists but can't be accessed

[chris-rands]

BPO	37318
Nosy	@rhettinger, @mdickinson, @chris-rands

^{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 2019-06-17.22:07:56.918>
created_at = <Date 2019-06-17.15:17:02.923>
labels = ['type-bug', 'invalid']
title = "builtins.True exists but can't be accessed"
updated_at = <Date 2019-06-18.15:59:27.078>
user = 'https://github.com/chris-rands'

bugs.python.org fields:

activity = <Date 2019-06-18.15:59:27.078>
actor = 'mark.dickinson'
assignee = 'none'
closed = True
closed_date = <Date 2019-06-17.22:07:56.918>
closer = 'rhettinger'
components = []
creation = <Date 2019-06-17.15:17:02.923>
creator = 'ChrisRands'
dependencies = []
files = []
hgrepos = []
issue_num = 37318
keywords = []
message_count = 3.0
messages = ['345863', '345927', '345993']
nosy_count = 3.0
nosy_names = ['rhettinger', 'mark.dickinson', 'ChrisRands']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue37318'
versions = []

[chris-rands]

On Python 3:

>>> import builtins
>>> 'True' in dir(builtins)
True
>>> builtins.True
  File "<stdin>", line 1
    builtins.True
                ^
SyntaxError: invalid syntax
>>> 

So "True" is a keyword, I guess this explains the behaviour, but still seems odd to me?

Relevant SO question:
https://stackoverflow.com/questions/56633402/why-are-true-and-false-being-set-in-globals-by-this-code

[rhettinger]

Depending on your mental model of the language, this may not seem odd at all.

>> # We can set any key/value pair in any dictionary
>> d = {'x': 10, 'True': 20, 'for': 30}

>>> # We can do regular string lookups at any time
>>> d['x']
10
>>> d['True']
20
>>> d['for']
30

>>> # globals() isn't special in this regard
>>> globals().update(d)
>>> globals()['x']
10
>>> globals()['True']
20
>>> globals()['for']
30

>>> # Globals is special though in that it provides
>>> # a fast way to do lookups for keys that are
>>> # valid identifiers and are not keywords
>>> x              # Fast lookup equivalent to globals['x']
10
>>> True           # This is a keyword, so there is no lookup
True
>>> for            # This is a keyword, so there is no lookup
SyntaxError: invalid syntax
    
At any rate, this isn't a bug.  It is just the way the language works.

Thank you for the report.

[mdickinson]

[Raymond]

It is just the way the language works.

As far as I can see, the language doesn't need these constants to be in builtins at all - the only reason for keeping them there is backwards compatibility.

As an experiment I tried removing True, False and None from bltinmodule.c, and recompiling, and every single test in the test suite passed just fine. So apparently we're not even testing for the existence of these constants.

It's also fun to note that it's still possible to modify these names:

>>> import builtins
>>> builtins.__dict__["True"] = False
>>> builtins.__dict__["True"] 
False

So I'm not sure what purpose having True, False and None in builtins serves.