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""" String Generator pattern parser """
import re
TOKEN_MATCHERS = [
("CHARCODE", r"\\([a-z])"),
("ONEOF", r"\[([a-zA-Z0-9]+)\]"),
("RANGE", r"\[(\w)-(\w)\]"),
("QUANTIFIER", r"\{(\d+)\}"),
("QUANTIFIER_RANGE", r"\{(\d*),(\d+)\}"),
("STRING_GROUP", r"\(([^|]([^)]+))\)"),
("NUMBER", r"\d+"),
("STRING", r"[a-zA-Z]+"),
("LITERAL", r"."),
]
def strtype(string):
""" Check string type
Arguments:
string: String to check
Returns:
Returns one of the following results
* DIGIT: String is digit [0-9]
* ALPHA: String is alpha [a-zA-Z]
* STRING: If no other match is found, it is assumed to be a STRING type
"""
if str.isdigit(string):
return "DIGIT"
if str.isalpha(string):
return "ALPHA"
return "STRING"
class Token: # pylint: disable=too-few-public-methods
""" Token class
Used by a tokenizer to store token data
Attributes:
group: Token group type or classification
value: Token value
pos: Starting position in input stream where token is found
"""
def __init__(self, group, value, pos=0):
self.group = group
self.value = value
self.pos = pos
class Tokenizer:
""" String Generator Tokenizer
Attributes:
string: String to tokenize
tokens: List of tokens after successful tokenization
"""
def __init__(self):
self.tokens = []
self.regex = "|".join("(?P<%s>%s)" % matcher for matcher in TOKEN_MATCHERS)
self._cursor = 0
def run(self, string=None):
""" Run tokenizer """
for match in re.finditer(self.regex, string):
group = match.lastgroup
value = match.group()
self.tokens.append(Token(group, value, match.start()))
def next(self):
""" Get next token
Retrieve next token and move cursor forward.
Returns:
A Token instance
"""
if self._cursor >= len(self.tokens):
return None
token = self.tokens[self._cursor]
self._cursor += 1
return token
def peek(self):
""" Peek at the next token
Retrieve next token without moving cursor forward.
Returns:
A Token instance
"""
if self._cursor >= len(self.tokens):
return None
return self.tokens[self._cursor]
class SGParser:
""" String Generator Pattern parser """
def __init__(self, tokenizer=None):
self.tokenizer = tokenizer
def _repeat(self):
ahead = self.tokenizer.peek()
if ahead and ahead.group == "QUANTIFIER":
result = self.parse_QUANTIFIER(self.tokenizer.next())
elif ahead and ahead.group == "QUANTIFIER_RANGE":
result = self.parse_QUANTIFIER_RANGE(self.tokenizer.next())
else:
result = {"type": "QUANTIFIER", "value": 1}
return result
def parse_STRING(self, token): # pylint: disable=invalid-name, no-self-use
""" Parse a STRING token
Returns:
Dictionary representing the AST node structure for string
"""
return {"type": token.group, "value": token.value}
def parse_RANGE(self, token): # pylint: disable=invalid-name
""" Parse a RANGE token
Returns:
Dictionary representing the AST node structure for range
"""
(start, end) = re.search(r"\[([a-zA-Z0-9])-([a-zA-Z0-9])\]", token.value).groups()
if start > end or strtype(start) != strtype(end):
raise ValueError("Invalid range %s at position %d" % (token.value, token.pos))
result = {"type": token.group,
"value": {
"start": start,
"end": end,
},
"repeat": self._repeat()}
return result
def parse_QUANTIFIER(self, token): # pylint: disable=invalid-name, no-self-use
""" Parse a QUANTIFIER token
Returns:
Dictionary representing the AST node structure for quantifier
"""
value = re.match(r"\{(\d+)\}", token.value).group(1)
return {"type": token.group, "value": int(value)}
def parse_CHARCODE(self, token): # pylint: disable=invalid-name
""" Parse a CHARCODE token
Returns:
Dictionary representing the AST node structure for charcode
"""
value = re.match(r"\\([a-z])", token.value).group(1)
return {"type": token.group, "value": value, "repeat": self._repeat()}
def parse_ONEOF(self, token): # pylint: disable=invalid-name
""" Parse a ONEOF token
Returns:
Dictionary representing the AST node structure for oneof
"""
values = re.findall("[a-zA-Z0-9]", token.value)
return {"type": token.group, "value": values, "repeat": self._repeat()}
def parse_QUANTIFIER_RANGE(self, token): # pylint: disable=invalid-name, no-self-use
""" Parse a QUANTIFIER_RANGE token
Returns:
Dictionary representing the AST node structure for quantifier range
"""
(start, end) = re.search(r"\{(\d+),(\d+)\}", token.value).groups()
if int(start) > int(end):
raise ValueError("Invalid range %s at %d" % (token.value, token.pos))
return {"type": token.group, "value": {"start": int(start), "end": int(end)}}
def parse_STRING_GROUP(self, token): # pylint: disable=invalid-name
""" Parse a STRING_GROUP token
Returns:
Dictionary representing the AST node structure for string group
"""
options = re.match(r"\((.+)\)", token.value).group(1)
values = re.split(r"\|", options)
return {"type": token.group, "value": values, "repeat": self._repeat()}
def parse_NUMBER(self, token): # pylint: disable=invalid-name
""" Parse a NUMBER token
Returns:
Dictionary representing the AST node structure for number
"""
return {"type": token.group, "value": int(token.value), "repeat": self._repeat()}
def parse_LITERAL(self, token): # pylint: disable=invalid-name, no-self-use
""" Parse a LITERAL token
Returns:
Dictionary representing the AST node structure for literal
"""
return {"type": "LITERAL", "value": token.value}
def parse(self, string):
""" Main parser method
Parses a list of tokens into an AST
Arguments:
string: The string to be parsed
Returns:
Dictionary representing the String Generator pattern AST
"""
ast = []
self.tokenizer.run(string)
token = self.tokenizer.next()
while token:
function_name = "parse_" + token.group
if not hasattr(self, function_name):
function_name = "parse_LITERAL"
func = getattr(self, function_name)
ast.append(func(token))
token = self.tokenizer.next()
return ast
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