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What this article shares with you is about the related functions that are not directly used in the process of running Python. The editor thinks it is very practical, so I share it with you to learn. I hope you can get something after reading this article.

We all know that in the process of running Python, it is not necessary to directly use the relevant contents of Grammar files for related syntax analysis, and the process will rely on the data structures in graminit.c/graminit.h for syntax analysis.

As mentioned earlier, under the source code directory of Python, there is a Grammar directory with only one file, Grammar, which defines all the syntax of Python in the syntax of BNF. Take the if statement, for example:

If_stmt: 'if' test': 'suite

('elif' test': 'suite) * [' else'': 'suite]

The above statement can be understood in this way, the if statement is the if keyword + logical expression +':'+ statement block (suite) followed by 0 or more elif statements and ends with else statements. The leftmost if_stmt indicates that this sentence defines if_stmt (non-Terminator), and on the right is the specific counterpart of if_stmt.

1. The content in the quotation marks is the actual string, and the if' represents the two characters if

two。 General markers represent non-terminators, that is, on the left side of an equation, if_stmt, test, and suite are all non-terminators, which can be extended to the sequence on the right side of the equation.

3. () parentheses are atomic operators, and those enclosed in parentheses are treated as a single expression

4. * stands for 0 or more, for example, ('elif' test': 'suite) * in if_stmt indicates that there can be 0 or more elif clauses in an if statement

5. + represents 1 or more

However, this document is not just used as a reference. In fact, the Python runtime also needs to indirectly utilize the contents of the Grammar file for parsing.

Python PGEN

There is code similar to the following in both Makefile.pre.in and Parser/grammar.mak:

# # #

# # #

# Grammar

GRAMMAR_H= $(srcdir) / Include/graminit.h

GRAMMAR_C= $(srcdir) / Python/graminit.c

GRAMMAR_INPUT= $(srcdir) / Grammar/Grammar

# # #

# #

# Parser

PGEN= Parser/pgen$ (EXE)

POBJS=\

Parser/acceler.o\

Parser/grammar1.o\

Parser/listnode.o\

Parser/node.o\

Parser/parser.o\

Parser/parsetok.o\

Parser/bitset.o\

Parser/metagrammar.o\

Parser/firstsets.o\

Parser/grammar.o\

Parser/pgen.o

PARSER_OBJS= $(POBJS) Parser/myreadline.o Parser/tokenizer.o

PGOBJS=\

Objects/obmalloc.o\

Python/mysnprintf.o\

Parser/tokenizer_pgen.o\

Parser/printgrammar.o\

Parser/pgenmain.o

PGENOBJS= $(PGENMAIN) $(POBJS) $(PGOBJS)

# # #

#

# Special rules for object files

(GRAMMAR_H) $(GRAMMAR_C): $(PGEN) $(GRAMMAR_INPUT)

-$(PGEN) $(GRAMMAR_INPUT) $(GRAMMAR_H) $(GRAMMAR_C)

(PGEN): $(PGENOBJS)

$(CC) $(OPT) $(LDFLAGS) $(PGENOBJS) $(LIBS)-o $(PGEN)

This code is responsible for generating pgen, and then calling pgen to generate graminit.h/graminit.c with Grammar as input. PGEN is a tool for parsing data generation that comes with Python, which is responsible for analyzing Grammar and then generating the corresponding graminit.c/graminit.h. Then, when Python runs, it relies on the data structures in graminit.c/graminit.h for parsing.

The above are the related functions that are not directly used in the process of running Python, and the editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

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