A while back, I wrote a simple calculator in Ruby. A few minutes ago I ran into a similar question in Stackoverflow, and decided to implement the Python version:

def is_number(s):
try:
float(s)
return True
except ValueError:
return False
def calc(expr):
if is_number(expr):
return float(expr)
arr = expr.split('+')
if len(arr) > 1:
return sum(map(calc, arr))
arr = expr.split('-')
if len(arr) > 1:
return reduce(lambda x,y: x-y, map(calc, arr))
arr = expr.split('*')
if len(arr) > 1:
return reduce(lambda x,y: x*y, map(calc, arr), 1)
arr = expr.split('/')
if len(arr) > 1:
return reduce(lambda x,y: x/y, map(calc, arr))
print calc("3+4-2 *2/ 2") # 5

Nice, isn’t it?

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