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import re
import base64
import binascii
import re
# Partial implementation of Rivest's proposed S-Expressions standard
# as documented at
# http://people.csail.mit.edu/rivest/Sexp.txt
#
# It's slightly optimized.
#
# Not implemented:
# [display hints]
# {basic transport}
__all__ = [ 'FormatError', 'parse' ]
class FormatError(Exception):
"""Raised when parsing fails."""
pass
_TOKEN_PAT = r"[a-zA-Z\-\.\/\_\:\*\+\=][a-zA-Z0-9\-\.\/\_\:\*\+\=]*"
# Regular expression to match a single lexeme from an encode s-expression.
_LEXEME_START_RE = re.compile(
r""" \s* (?: (%s) | # Grp 0: A token.
([0-9]*(?: [\:\|\#\{] | # Grp1 : start of string...
\"(?:[^\\\"]+|\\.)*\")) | # or qstring.
([\(\)]) # Grp 2: a paren of some kind.
)"""
%_TOKEN_PAT,re.X|re.M|re.S)
class _P:
"""Helper class for parenthesis tokens."""
def __init__(self, val):
self.val = val
def __repr__(self):
return "_P(%r)"%self.val
_OPEN_PAREN = _P("(")
_CLOSE_PAREN = _P(")")
del _P
_SPACE_RE = re.compile(r'\s+')
# Matches all characters in a string that we need to unquote.
_UNQUOTE_CHAR_RE = re.compile(r'''
\\ (?: [abtnvfr] | \r \n ? | \n \r ? | [xX] [A-Fa-f0-9]{2} | [0-8]{1,3} )
''')
# Map from quoted representation to unquoted format.
_UNQUOTE_CHAR_MAP = { 'a': '\a',
'b': '\b',
't': '\t',
'n': '\n',
'v': '\v',
'f': '\f',
'r': '\r' }
def _unquoteChar(ch, _U=_UNQUOTE_CHAR_MAP):
ch = ch[1:]
try:
return _U[ch]
except KeyError:
pass
if ch[0] in "\n\r":
return ""
elif ch[0] in 'xX':
return chr(int(ch[1:], 16))
else:
i = int(ch[1:], 8)
if i >= 256:
raise FormatError("Octal character format out of range.")
return chr(i)
def _lexItems(s):
"""Generator that iterates over the lexical items in an encoded
s-expression. Yields a string for strings, or the special objects
_OPEN_PAREN and _CLOSE_PAREN.
>>> list(_lexItems('(4:a)b hello) (world 1:a 0: '))
[_P('('), 'a)b ', 'hello', _P(')'), _P('('), 'world', 'a', '']
>>> list(_lexItems('a b-c 1#20#2#2061##686877# |aGVsbG8gd29ybGQ|'))
['a', 'b-c', ' ', ' a', 'hhw', 'hello world']
>>> list(_lexItems('#2 0# |aGVs\\nbG8 gd29yb GQ| '))
[' ', 'hello world']
>>> list(_lexItems('|YWJjZA==| x |YWJjZA| 3|Y W J j|'))
['abcd', 'x', 'abcd', 'abc']
>>> list(_lexItems('("1""234""hello world" 3"abc" 4" " )'))
[_P('('), '1', '234', 'hello world', 'abc', ' ', _P(')')]
"""
s = s.strip()
while s:
m = _LEXEME_START_RE.match(s)
if not m:
raise FormatError("No pattern match at %r"%s[:30])
g = m.groups()
if g[2]:
if g[2] == "(":
yield _OPEN_PAREN
else:
yield _CLOSE_PAREN
s = s[m.end():]
elif g[0]:
# we have a token. Go with that.
yield g[0]
s = s[m.end():]
else:
assert g[1]
lastChar = g[1][-1]
if lastChar == '"':
qidx = g[1].index('"')
quoted = g[1][qidx+1:-1] # All but quotes.
data = _UNQUOTE_CHAR_RE.sub(_unquoteChar, quoted)
if qidx != 0:
num = int(g[1][:qidx], 10)
if num != len(data):
raise FormatError("Bad length on quoted string")
yield data
s = s[m.end():]
continue
num = g[1][:-1]
if len(num):
num = int(num, 10)
else:
num = None
if lastChar == ':':
if num is None:
raise FormatError()
s = s[m.end():]
if len(s) < num:
raise FormatError()
yield s[:num]
s = s[num:]
elif lastChar == '#':
s = s[m.end():]
try:
nextHash = s.index('#')
except ValueError:
raise FormatError("Unterminated # string")
dataStr = _SPACE_RE.sub("", s[:nextHash])
try:
data = binascii.a2b_hex(dataStr)
except TypeError:
raise FormatError("Bad hex string")
if num is not None and len(data) != num:
raise FormatError("Bad number on hex string")
yield data
s = s[nextHash+1:]
elif lastChar == '|':
s = s[m.end():]
try:
nextBar = s.index('|')
except ValueError:
raise FormatError("Unterminated | string")
dataStr = _SPACE_RE.sub("", s[:nextBar])
# Re-pad.
mod = len(dataStr) % 4
if mod:
dataStr += "=" * (4 - mod)
try:
data = binascii.a2b_base64(dataStr)
except TypeError:
raise FormatError("Bad base64 string")
if num is not None and len(data) != num:
raise FormatError("Bad number on base64 string")
yield data
s = s[nextBar+1:]
else:
assert None
def parse(s):
"""
>>> parse("()")
[]
>>> parse("(1:X3:abc1:d)")
['X', 'abc', 'd']
>>> parse("(1:X((3:abc))1:d)")
['X', [['abc']], 'd']
>>> parse("(a b (d\\ne f) (g) #ff00ff# |aGVsbG8gd29ybGQ|)")
['a', 'b', ['d', 'e', 'f'], ['g'], '\\xff\\x00\\xff', 'hello world']
"""
outermost = []
stack = [ ]
push = stack.append
pop = stack.pop
add = outermost.append
for item in _lexItems(s):
if item is _OPEN_PAREN:
next = []
add(next)
push(add)
add = next.append
elif item is _CLOSE_PAREN:
add = pop()
else:
# it's a string.
add(item)
if len(outermost) != 1:
raise FormatError("No enclosing parenthesis on list")
return outermost[0]
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