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encukou merged 8 commits into from
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gh-127833: Reword and expand the Notation section #134443

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gh-127833: Reword and expand the Notation section
encukou May 21, 2025
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Consolidate with the Full Grammar intro
encukou May 21, 2025
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Don't link the examples
encukou May 21, 2025
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encukou May 21, 2025
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Note practical difference between syntactic & lexical definitions
encukou May 28, 2025
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encukou Jun 3, 2025
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Constrain `"a"..."z"` and `<...>` to lexical definitions
encukou Jun 4, 2025
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Update Doc/reference/introduction.rst
encukou Jun 7, 2025
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Note practical difference between syntactic & lexical definitions 
Co-authored-by: Blaise Pabon <blaise@gmail.com>
Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
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commit 231e2bae7e1de58f96029c015e865326b66c8f81
26 changes: 16 additions & 10 deletions Doc/reference/introduction.rst
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Expand Up @@ -183,13 +183,19 @@ This does *not* mean that there is an empty first alternative.

.. index:: lexical definitions

.. note::

There is some difference between *lexical* and *syntactic* analysis:
the :term:`lexical analyzer` operates on the individual characters of the
input source, while the *parser* (syntactic analyzer) operates on the stream
of :term:`tokens <token>` generated by the lexical analysis.
However, in some cases the exact boundary between the two phases is a
CPython implementation detail.

This documentation uses the same BNF grammar for both.
There is some difference between *lexical* and *syntactic* analysis:
the :term:`lexical analyzer` operates on the individual characters of the
input source, while the *parser* (syntactic analyzer) operates on the stream
of :term:`tokens <token>` generated by the lexical analysis.
However, in some cases the exact boundary between the two phases is a
CPython implementation detail.

The practical difference between the two is that in *lexical* definitions,
all whitespace is significant.
The lexical analyzer :ref:`discards <whitespace>` all whitespace that is not
converted to tokens like :data:`token.INDENT` or :data:`~token.NEWLINE`.
*Syntactic* definitions then use these tokens, rather than source characters.

This documentation uses the same BNF grammar for both styles of definitions.
All uses of BNF in the next chapter (“Lexical Analysis”) are lexical definitions;
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uses in subsequent chapters are syntactic definitions.