Ich bastle gerade einen einfachen Interpreter, der bisher additionsbefehle ausführt. Für die Eingabe wird ein Fehler geworfen:
File "interpreter.py", line 111, in parseInt
return int(result)
ValueError: invalid literal for int() with base 10: ''
Ich verstehe nicht warum, denn der Eingabestring hat keine whitespaces. Kann mir jemand sagen was falsch ist?
Code: Alles auswählen
# Token types
#
# EOF (end-of-file) token is used to indicate that
# there is no more input left for lexical analysis
INTEGER, PLUS, EOF = 'INTEGER', 'PLUS','EOF'
class Token(object):
def __init__(self, type, value):
# token type: INTEGER, PLUS, or EOF
self.type = type
# token value: 0, 1, 2. 3, 4, 5, 6, 7, 8, 9, '+', or None
self.value = value
def __str__(self):
"""
String representation of the class instance.
Examples:
Token(INTEGER, 3)
Token(PLUS '+')
"""
return 'Token({type}, {value})'.format(
type=self.type,
value=repr(self.value)
)
def __repr__(self):
return self.__str__()
class Interpreter(object):
def __init__(self, text):
# client string input, e.g. "3+5"
self.text = text
# self.pos is an index into self.text
self.pos = 0
# current token instance
self.current_token = None
self.current_char = self.text[self.pos]
def error(self):
raise Exception('Error parsing input')
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.
"""
text = self.text
# is self.pos index past the end of the self.text ?
# if so, then return EOF token because there is no more
# input left to convert into tokens
if self.pos > len(text) - 1:
return Token(EOF, None)
# get a character at the position self.pos and decide
# what token to create based on the single character
current_char = text[self.pos]
while (current_char == " "):
self.pos +=1
current_char = text[self.pos]
# if the character is a digit then convert it to
# integer, create an INTEGER token, increment self.pos
# index to point to the next character after the digit,
# and return the INTEGER token
if current_char.isdigit():
token = Token(INTEGER, self.parseInt())
return token
if current_char == '+':
token = Token(PLUS, current_char)
self.pos += 1
return token
if current_char == ' ':
self.pos += 1
return None
self.error()
def eat(self, token_type):
# compare the current token type with the passed token
# type and if they match then "eat" the current token
# and assign the next token to the self.current_token,
# otherwise raise an exception.
if self.current_token.type == token_type:
self.current_token = self.get_next_token()
else:
self.error()
def advance(self):
self.pos += 1
if self.pos > len(self.text)-1:
self.current_char = None
else:
self.current_char = self.text[self.pos]
def parseInt(self):
result = ""
while self.current_char is not None and self.current_char.isdigit():
result += self.current_char
self.advance()
print(result)
return int(result)
def expr(self):
"""expr -> INTEGER PLUS INTEGER"""
# set current token to the first token taken from the input
self.current_token = self.get_next_token()
# we expect the current token to be a single-digit integer
lval = self.current_token
self.eat(INTEGER)
# we expect the current token to be a '+' token
self.current_token = self.get_next_token()
self.eat(PLUS)
# we expect the current token to be a single-digit integer
self.current_token = self.get_next_token()
rval = self.current_token
self.eat(INTEGER)
# after the above call the self.current_token is set to
# EOF token
# at this point INTEGER PLUS INTEGER sequence of tokens
# has been successfully found and the method can just
# return the result of adding two integers, thus
# effectively interpreting client input
result = lval + rval
return result
def main():
while True:
try:
# To run under Python3 replace 'raw_input' call
# with 'input'
text = input('calc> ')
except EOFError:
break
if not text:
continue
interpreter = Interpreter(text)
result = interpreter.expr()
print(result)
if __name__ == '__main__':
main()
