Python SEXP IO

experiments/python/.gitignore

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+*.pyc

experiments/python/hop/sexp.py

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+## Copyright 2010, 2011, 2012 Tony Garnock-Jones <tonygarnockjones@gmail.com>.
+##
+## This file is part of Hop.
+##
+## Hop is free software: you can redistribute it and/or modify it
+## under the terms of the GNU General Public License as published by
+## the Free Software Foundation, either version 3 of the License, or
+## (at your option) any later version.
+##
+## Hop is distributed in the hope that it will be useful, but WITHOUT
+## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+## or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+## License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with Hop.  If not, see <http://www.gnu.org/licenses/>.
+
+# SPKI SEXP
+
+import StringIO
+
+class SyntaxError(Exception): pass
+
+def write_sexp_str(f, x):
+    f.write(str(len(x)))
+    f.write(':')
+    f.write(x)
+
+def write_sexp(f, sexp):
+    if type(sexp) is list:
+        f.write('(')
+        for x in sexp: write_sexp(f, x)
+        f.write(')')
+        return
+    if type(sexp) is str:
+        write_sexp_str(f, sexp)
+        return
+    if type(sexp) is tuple:
+        f.write('[')
+        write_sexp_str(f, sexp[0])
+        f.write(']')
+        write_sexp_str(f, sexp[1])
+        return
+
+def skipws(f):
+    while True:
+        c = f.read(1)
+        if not c.isspace(): return c
+
+def read_sexp(f):
+    c = skipws(f)
+    if c == '(':
+        l = []
+        while True:
+            val = read_sexp(f)
+            if val is None: return l
+            l.append(val)
+    if c == '[':
+        h = read_sexp(f)
+        c = skipws(f)
+        if c != ']': raise SyntaxError("Missing hint close bracket")
+        b = read_sexp(f)
+        return (h, b)
+    if c.isdigit():
+        size = ord(c) - 48
+        while True:
+            c = f.read(1)
+            if c == ':': return f.read(size)
+            if not c.isdigit(): raise SyntaxError("Illegal character in byte vector length")
+            size = size * 10 + ord(c) - 48
+    if c == ')':
+        return None
+    raise SyntaxError("Illegal character in sexp")
+
+def parse(s):
+    return read_sexp(StringIO.StringIO(s))