Bencode Decode

bencode.py

# Here c refer to content ,p refer to the pointer
# or the length of parsed text

DEBUG = True
decode_func = {}

def print_debug(fn):
	def wrapper(c,p):
		if DEBUG:
			print(fn.__name__)
		return fn(c,p)
	return wrapper

@print_debug
def decode_int(c,p):
	p += 1
	end = c.index(b'e',p)
	num = int(c[p:end])
	if c[p+1] == b'-':
		if c[p+2] == b'0':
			raise ValueError
		num = -num
	return num,end+1

@print_debug
def decode_string(c,p):
	colon = c.index(b':',p)
	length = int(c[p:colon])
	string = c[colon+1:colon+1+length]
	return string,colon+length+1

@print_debug
def decode_list(c,p):
	result = []
	p += 1
	while c[p] != ord(b'e'):
		t,p = decode_func[c[p]](c,p)
		result.append(t)
	return result,p+1

@print_debug
def decode_dict(c,p):
	result = {}
	p += 1
	while c[p] != ord(b'e'):
		key,p = decode_string(c,p)
		value,p = decode_func[c[p]](c,p)
		result[key] = value
	return result,p+1

def decode(c):
	p = 0
	return decode_func[c[p]](c,p)[0]

decode_func[ord(b'i')] = decode_int
decode_func[ord(b'l')] = decode_list
decode_func[ord(b'd')] = decode_dict
for i in b'0123456789':
	decode_func[i] = decode_string