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SET, GET, ALIAS = ("SET", "GET", "ALIAS")
INTEGER = "INTEGER"
EOF = "EOF"
class Token(object):
def __init__(self, type, value):
self.type = type
self.value = value
def __str__(self):
return f"Token({self.type}, {self.value}"
def __repr__(self) -> str:
return self.__str__()
class Lexer(object):
def __init__(self, text):
self.text = text
self.pos = 0
self.current_char = self.text[self.pos]
def error(self):
raise Exception("Invalid Character")
def advance(self):
"""Advance the `pos` pointer and set the `current_char` variable."""
self.pos += 1
if self.pos > len(self.text) - 1:
self.current_char = None # Indicates end of input
else:
self.current_char = self.text[self.pos]
def skip_whitespace(self):
while self.current_char is not None and self.current_char.isspace():
self.advance()
def integer(self):
"""Return a (multidigit) integer consumed from the input."""
result = ""
while self.current_char is not None and self.current_char.isdigit():
result += self.current_char
self.advance()
return int(result)
def get_next_token(self):
"""Lexical analyzer (also known as scanner or tokenizer)
This method is responsible for breaking a sentence
apart into tokens. One token at a time.
"""
while self.current_char is not None:
if self.current_char.isspace():
self.skip_whitespace()
continue
if self.current_char.isdigit():
return Token(INTEGER, self.integer())
if self.current_char == "get":
self.advance()
return Token(GET, "get")
if self.current_char == "set":
self.advance()
return Token(SET, "set")
if self.current_char == "Alias":
self.advance()
return Token(ALIAS, "Alias")
self.error()
return Token(EOF, None)
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