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initial attempt implementing the go template lexer in Python
from collections import namedtuple
# A token has
# type: one of the TOK_* constants
# value: string value, as taken from input
Token = namedtuple('Token', 'type value')
class LexerError(Exception): pass
class TemplateLexer(object):
""" A lexer for the template language. Initialize with the input
string, and then call lex() which generates tokens. None is
generated at EOF (and the generator expires).
def __init__(self, input):
self.input = input
self.pos = 0
self.curstart = 0
self.state = self._lex_text
def lex(self):
while self.state:
self.state = yield from self.state()
#--------- Internal ---------#
_LEFT_META = '{{'
_RIGHT_META = '}}'
def _eof(self):
return self.pos >= len(self.input)
def _emit(self, toktype):
tok = Token(toktype, self.input[self.curstart:self.pos])
self.curstart = self.pos
return tok
def _lex_text(self):
while not self._eof():
if self.input.startswith(self._LEFT_META, self.pos):
# {{ here. Emit the text we've seen so far.
if self.pos > self.curstart:
yield self._emit(TOK_TEXT)
return self._lex_left_meta
self.pos += 1 # ZZZ: can't just find to next {{ here?
# Reached EOF. Emit trailing text.
if self.pos > self.curstart:
yield self._emit(TOK_TEXT)
# Yielding None to signal EOF to the consumer.
# Returning None to stop the main lexing loop
yield None
return None
def _lex_left_meta(self):
self.pos += len(self._LEFT_META)
yield self._emit(TOK_LEFT_META)
return self._lex_inside_action
def _lex_right_meta(self):
self.pos += len(self._RIGHT_META)
yield self._emit(TOK_RIGHT_META)
return self._lex_text
def _lex_inside_action(self):
while not self._eof():
if self.input.startswith(self._RIGHT_META, self.pos):
yield self._emit(TOK_DUMMY)
return self._lex_right_meta
self.pos += 1
# Reached EOF
raise LexerError('Unterminated action')
return None
if __name__ == '__main__':
text = r'''
Some text here {{range $s.Text}} and here {{1.2 "%g"}} too {{.}}
text = r'''
Some text here {{action}} and here {{action2}}'''
tlex = TemplateLexer(text)
for t in tlex.lex():
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