pPEGpy 0.3.3

pPEG -- portable PEG in Python

pPEGpy

This is an implementation of a portable PEG parser in Python.

For documentation see pPEG, the portable PEG project.

The pPEGpy package can be installed from PyPi with:

> pip install pPEGpy

Note the spelling of pPEGpy, there are unrelated packages with similar names.

For other ways to use the pPEGpy grammar-parser see the Package Notes below.

Example

from pPEGpy import peg

sexp = peg.compile("""
    sexp  = _ list
    list  = '(' _ elem* ')' _
    elem  = list / atom _
    atom  = ~[() \t\n\r]+
    _     = [ \t\n\r]*
""")

test = """
    (foo bar (blat 42) (f(g(x))))
"""

p = sexp.parse(test)

print(p)

This prints a parse tree diagram:

list
│ atom 'foo'
│ atom 'bar'
│ list
│ │ atom 'blat'
│ │ atom '42'
│ list
│ │ atom 'f'
│ │ list
│ │ │ atom 'g'
│ │ │ atom 'x'

Application can use a ptree:

ptree = p.tree()

print(ptree)  # =>

["list",[["atom","foo"],["atom","bar"],
    ["list",[["atom","blat"],["atom","42"]]],
    ["list",[["atom","f"],
        ["list",[["atom","g"],["atom","x"]]]]]]]

Another example:

from pPEGpy import peg

# Equivalent to the regular expression for well-formed URI's in RFC 3986.

pURI = peg.compile("""
    URI     = (scheme ':')? ('//' auth)? path ('?' query)? ('#' frag)?
    scheme  = ~[:/?#]+
    auth    = ~[/?#]*
    path    = ~[?#]*
    query   = ~'#'*
    frag    = ~[ \t\n\r]*
""")

test = "http://www.ics.uci.edu/pub/ietf/uri/#Related"
uri = pURI.parse(test)

print(uri)

URI
│ scheme 'http'
│ auth 'www.ics.uci.edu'
│ path '/pub/ietf/uri/'
│ frag 'Related'

ptree:

["URI",[["scheme","http"],["auth","www.ics.uci.edu"],
        ["path","/pub/ietf/uri/"],["frag","Related"]]]

Usage

Common usage:

    from pPEGpy import peg

    my_parser = peg.compile(""... my pPEG grammar rules...""")

    # -- use my-parser in my application .......

    my_parse = my_parser.parse('...input string...}')

    if not my_parse.ok:
        print(my_parse.err)
        .... handle parse failure ... 
    else:    
        ptree = my_parse.tree()
        process(ptree)

The ptree parse tree type is JSON data, as defined in pPEG.

Package Notes

To experiment you can clone the GitHub repository pPEGpy.

These command lines can be used to build a local package:

> cd <your pPEGpy directory>
> uv init --lib
> uv build
> pip install -e .

The -e option allows local editing of the local files.

The repo includes an examples/ folder, try running the date.py for example.

Bare File

The peg.py file in: pPEGpy/src/pPEGy/peg.py is the only file you really need.

If you put a copy of this file into a folder together with your own programs you can import the grammar-parser directly with import peg. Very simple and easy.

But that does not work across directories, to import the bare peg.py file from another directory requires a hack like this:

import sys
sys.path.insert(1, <path to your copy of peg.py>)
import peg

To avoid that (at the cost of all the Python packaging complications!) you can build a package pPEGpy and install it with pip, as above.

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