Python
Number of characters: 237
Fully obfuscated function:
from operator import*
def e(s,l=[]):
if s:l+=list(s.replace(' ','')+')')
a=0;o=add;d=dict(zip(')*+-/',(0,mul,o,sub,div)));p=l.pop
while o:
c=p(0)
if c=='(':c=e(0)
while l[0]not in d:c+=p(0)
a=o(a,float(c));o=d[p(0)]
return a
Clear/semi-obfuscated function:
import operator
def calc(source, stack=[]):
if source:
stack += list(source.replace(' ', '') + ')')
answer = 0
ops = {
')': 0,
'*': operator.mul,
'+': operator.add,
'-': operator.sub,
'/': operator.div,
}
op = operator.add
while op:
cur = stack.pop(0)
if cur == '(':
cur = calc(0)
while stack[0] not in ops:
cur += stack.pop(0)
answer = op(answer, float(cur))
op = ops[stack.pop(0)]
return answer
