parse-ebnf’s documentation

Introduction

parse-ebnf is a parser for EBNF, Extended Backus-Naur Form. Give it an EBNF input and it will generate a parse tree.

Note

This package does not generate a parser for the described grammar.

Installation

pip install parse-ebnf

Quick start

from parse_ebnf.parsing import ParsingError, parse_file

try:
    #Your EBNF file goes here.
    pt = parse_file(ebnf_path)
    partial = False
except ParsingError as e:
    #If an exception occurs, a partial tree is generated. See the docs for
    #details.
    pt = e.parser.pt
    partial = True

#Prints the text that the tree was parsed from.
print(str(pt))
#Prints a debug view of the tree.
print(repr(pt))

print(f'Parsing the file created a tree with {pt.count} nodes.')
print(f'The tree has a height of {pt.height}.')
print(f'Each node in the tree has at MOST {pt.maxDegree} children.')

def DepthFirst(node, partial, func):
    #Partial nodes are in a mostly undefined state.
    if not partial: func(node)
    for child in node.children:
        #If a node is partial, then its last child is partial. All other
        #children are not partial.
        if partial and child is node.children[-1]:
            DepthFirst(child, True, func)
        else:
            DepthFirst(child, False, func)

#This will visit each node in the parse tree and print the line where its
#text begins.
DepthFirst(pt.root, partial, lambda node: print(node.startLine))

from parse_ebnf.nodes import Comment

#Finds each comment in the file and prints its text content.
for child in pt.root.children:
    if isinstance(child, Comment):
        #A tree being partial means that its root is partial.
        if partial and child is pt.root.children[-1]: continue
        print(str(child))

Indices and tables