Some of the inspiration and wording is taken from the text of PEP 498 by Eric
V. Smith, and the existing str.format() documentation.

Microbenchmarks show 2-2.5x improvement.  Built-in 'divmod' function
is now also ~10% faster.

-m timeit -s "x=22331" "x//2;x//-3;x//4;x//5;x//-6;x//7;x//8;x//-99;x//100;"
with patch: 0.321          without patch: 0.633

-m timeit -s "x=22331" "x%2;x%3;x%-4;x%5;x%6;x%-7;x%8;x%99;x%-100;"
with patch: 0.224          without patch: 0.66

Big thanks to Serhiy Storchaka, Mark Dickinson and Victor Stinner for
thorow code reviews and algorithms improvements.

Different solution from 3.5.

protocol for the os.scandir() iterator.

no ResourceWarning is emitted.

no ResourceWarning is emitted.

to format short Python version.

PyArg_ParseTupleAndKeywords().  RuntimeError did raised before in some
programming bugs.

if the stack is too deep.

if the stack is too deep.

The original form is incorrect grammar and feels awkward, even though the
meaning is clear.

Patch by Anish Shah.

Issue #26204: the compiler doesn't emit SyntaxWarning warnings anymore when
constant statements are ignored.

not have a math vocabulary.

not have a math vocabulary.

The compile ignores constant statements and emit a SyntaxWarning warning.

Don't emit the warning for string statement because triple quoted string is a
common syntax for multiline comments.

Don't emit the warning on ellipis neither: 'def f(): ...' is a legit syntax for
abstract functions.

Changes:

* test_ast: ignore SyntaxWarning when compiling test statements. Modify
  test_load_const() to use assignment expressions rather than constant
  expression.
* test_code: add more kinds of constant statements, ignore SyntaxWarning when
  testing that the compiler removes constant statements.
* test_grammar: ignore SyntaxWarning on the statement "1"