What is __peg_parser__ in Python?

I was using the keyword built-in module to get a list of all the keywords of the current Python version. And this is what I did:

>>> import keyword
>>> print(keyword.kwlist)
['False', 'None', 'True', '__peg_parser__', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']

JavaScript
​x
 
>>> import keyword
>>> print(keyword.kwlist)
['False', 'None', 'True', '__peg_parser__', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']
​

And in the keyword.kwlist list there is __peg_parser__. So to see what it does, I type __peg_parser__ in a Python 3.9 interpreter on Windows (you’ll get the same output on Mac OS and Linux as well), and this is what is get:

>>> __peg_parser__
  File "<stdin>", line 1
    __peg_parser__
    ^
SyntaxError: You found it!

JavaScript
 
>>> __peg_parser__
  File "<stdin>", line 1
    __peg_parser__
    ^
SyntaxError: You found it!
​

So my question is, what is __peg_parser__ and why do I get SyntaxError: You found it!?

Answer

It was an easter egg related to the rollout of the new PEG parser. The easter egg, along with the old LL(1) parser, will be removed in 3.10.

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Answer