why gtk.Entry does not give me right answers?

[Lion Chen]

Hi, All,

i am trying write a calculator, now normal calculation works ok. but if
i enter long numbers, for example 333333333333333333 + 7, it gives me
"333333333333333312".....

there are 18 "3"s, if the length is more than 17, the calculation will
be wrong on Windows and Ubuntu.

the following is some of my codes:

def pre_calc(self, op):
#if entry is empty, any operators are invalid except "-"
if not self.entry.get_text() and op != "-":
return

if not self.entry.get_text() and op == "-":
self.entry.set_text(op)
self.cleared = 1
self.negative_sign = True#indicates there's already a "-"
return

#retrieve the 1st num and operator
if not self.op and self.entry.get_text():
if op != "=":
self.op = op
#print "text typ:", type(self.entry.get_text())
self.first_num = self.entry.get_text()
self.cleared = 0 # ready to input 2nd num
#print "op:", self.op, "-----", "1st num:", self.first_num
return
else:
self.first_num = None
self.second_num = None
self.op = None
self.cleared = 0
self.negative_sign = False
return

#retrieve the second num and begin calculation
elif self.op and self.first_num and self.entry.get_text() != "-":
if op == "=":
self.second_num = self.entry.get_text()
self.calc()
#reset the following varibles, awaiting next round of inputs
self.first_num = None
self.second_num = None
self.op = None
self.cleared = 0
self.negative_sign = False
return
elif op == "-":
if self.cleared == 1: #if user has input 2nd num already
self.second_num = self.entry.get_text()
self.calc()
self.first_num = self.entry.get_text()
self.op = op
self.cleared = 0
self.negative_sign = False
return
else:
self.entry.set_text(op)
self.cleared = 1
self.negative_sign = True#indicates there's already a "-"
return
else:
self.op = op
if self.cleared == 1:
self.second_num = self.entry.get_text()
self.calc()
self.first_num = self.entry.get_text()
self.cleared = 0
self.negative_sign = False
return
else:
return

def calc(self, unary_op = None):
if not unary_op:
if (not self.first_num) or (not self.second_num) or \
(not self.op):
return

result = None

calc_methods = {"+": self.add,
"-": self.subtract,
"*": self.multiply,
"/": self.divide,
"%": self.mod,
"pwr": self.power,
"|": self.b_or,
"&": self.b_and,
"^": self.b_exc,
"<<": self.b_lshift,
">>": self.b_rshift
}

unary_methods ={"~": self.b_invert,
"1/x": self.a_fraction,
"sqrt": self.sqrt
}

if not unary_op:
for op, method in calc_methods.items():
if self.op == op:
result = calc_methods[op]()
else:
for op, method in unary_methods.items():
if unary_op == op:
result = unary_methods[op]()

self.entry.set_text(result)

def add(self):
result = None
#if hex system
#print type(self.first_num)
if self.hdob["h"].get_active():
self.first_num = long(self.first_num, 16)
self.second_num = long(self.second_num, 16)
r = self.first_num + self.second_num

r = self.convert.d2h(r)

return r

#if decimal system
elif self.hdob["d"].get_active():
self.first_num = float(self.first_num)
self.second_num = float(self.second_num)
result = self.first_num + self.second_num

if result - long(result) == 0:
#print str(long(result))
return str(long(result))
else:
return str(result)

#if octal system
elif self.hdob["o"].get_active():
self.first_num = long(self.first_num, 8)
self.second_num = long(self.second_num, 8)
result = self.first_num + self.second_num

result = self.convert.d2o(result)

return result

else:
self.first_num = long(self.first_num, 2)
self.second_num = long(self.second_num, 2)
result = bin(self.first_num + self.second_num)

result = self.convert.d2b(result)

return result
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Read the PyGTK FAQ: http://faq.pygtk.org/

[Christian Mallwitz-2]

See http://www.codinghorror.com/blog/2009/05/why-do-computers-suck-at-math.html
and maybe http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

Christian
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Read the PyGTK FAQ: http://faq.pygtk.org/