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""" Pyparsing parser for BibTeX files
A standalone parser using pyparsing.
pyparsing has a simple and expressive syntax so the grammar is easy to read and
write.
Submitted by Matthew Brett, 2010
Simplified BSD license
"""
from pyparsing import (
Regex,
Suppress,
ZeroOrMore,
Group,
Optional,
Forward,
SkipTo,
CaselessLiteral,
Dict,
)
class Macro:
"""Class to encapsulate undefined macro references"""
def __init__(self, name):
self.name = name
def __repr__(self):
return f'Macro("{self.name}")'
def __eq__(self, other):
return self.name == other.name
# Character literals
LCURLY, RCURLY, LPAREN, RPAREN, QUOTE, COMMA, AT, EQUALS, HASH = map(
Suppress, '{}()",@=#'
)
def bracketed(expr):
"""Return matcher for `expr` between curly brackets or parentheses"""
return (LPAREN + expr + RPAREN) | (LCURLY + expr + RCURLY)
# Define parser components for strings (the hard bit)
chars_no_curly = Regex(r"[^{}]+")
chars_no_curly.leaveWhitespace()
chars_no_quotecurly = Regex(r'[^"{}]+')
chars_no_quotecurly.leaveWhitespace()
# Curly string is some stuff without curlies, or nested curly sequences
curly_string = Forward()
curly_item = Group(curly_string) | chars_no_curly
curly_string << LCURLY + ZeroOrMore(curly_item) + RCURLY
# quoted string is either just stuff within quotes, or stuff within quotes, within
# which there is nested curliness
quoted_item = Group(curly_string) | chars_no_quotecurly
quoted_string = QUOTE + ZeroOrMore(quoted_item) + QUOTE
# Numbers can just be numbers. Only integers though.
number = Regex("[0-9]+")
# Basis characters (by exclusion) for variable / field names. The following
# list of characters is from the btparse documentation
any_name = Regex("[^\\s\"#%'(),={}]+")
# btparse says, and the test bibs show by experiment, that macro and field names
# cannot start with a digit. In fact entry type names cannot start with a digit
# either (see tests/bibs). Cite keys can start with a digit
not_digname = Regex("[^\\d\\s\"#%'(),={}][^\\s\"#%'(),={}]*")
# Comment comments out to end of line
comment = AT + CaselessLiteral("comment") + Regex(r"[\s{(].*").leaveWhitespace()
# The name types with their digiteyness
not_dig_lower = not_digname.copy().setParseAction(lambda t: t[0].lower())
macro_def = not_dig_lower.copy()
macro_ref = not_dig_lower.copy().setParseAction(lambda t: Macro(t[0].lower()))
field_name = not_dig_lower.copy()
# Spaces in names mean they cannot clash with field names
entry_type = not_dig_lower("entry_type")
cite_key = any_name("cite_key")
# Number has to be before macro name
string = number | macro_ref | quoted_string | curly_string
# There can be hash concatenation
field_value = string + ZeroOrMore(HASH + string)
field_def = Group(field_name + EQUALS + field_value)
entry_contents = Dict(ZeroOrMore(field_def + COMMA) + Optional(field_def))
# Entry is surrounded either by parentheses or curlies
entry = AT + entry_type + bracketed(cite_key + COMMA + entry_contents)
# Preamble is a macro-like thing with no name
preamble = AT + CaselessLiteral("preamble") + bracketed(field_value)
# Macros (aka strings)
macro_contents = macro_def + EQUALS + field_value
macro = AT + CaselessLiteral("string") + bracketed(macro_contents)
# Implicit comments
icomment = SkipTo("@").setParseAction(lambda t: t.insert(0, "icomment"))
# entries are last in the list (other than the fallback) because they have
# arbitrary start patterns that would match comments, preamble or macro
definitions = Group(comment | preamble | macro | entry | icomment)
# Start symbol
bibfile = ZeroOrMore(definitions)
def parse_str(str):
return bibfile.parseString(str)
if __name__ == "__main__":
# Run basic test
txt = """
Some introductory text
(implicit comment)
@ARTICLE{Authors2011,
author = {First Author and Second Author and Third Author},
title = {An article about {S}omething},
journal = "Journal of Articles",
year = {2011},
volume = {16},
pages = {1140--1141},
number = {2}
}
"""
print("\n\n".join(defn.dump() for defn in parse_str(txt)))