Programming Forums > Script Programming > Python

kurt · Jan 30th, 2007, 3:04 AM

Let's say i want to perform a subtraction on a variable (say, Energy) by 5%, the shortest way i can think of is:

Tolerance = 0.05 * Energy
Energy = Energy - Tolerance

or

(Toggle Plain Text)

Energy = Energy - 0.05*(Energy)

I know it's already pretty short, but is there a shorter, elegant way?

Arevos · Jan 30th, 2007, 4:48 AM

I think the shortest you could get would be:

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energy -= 0.05 * energy

Or:

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energy *= 0.95

kurt · Jan 30th, 2007, 4:59 AM

I was hoping there's something like:

Gone = energy * 50%

grumpy · Jan 30th, 2007, 5:15 AM

If I'm understanding you right .....

(Toggle Plain Text)

   gone = energy*percentage;
   energy -= gone
   total_gone += gone

Arevos · Jan 30th, 2007, 6:52 AM

Quote:

Originally Posted by kurt

I was hoping there's something like:

Gone = energy * 50%

Nope, unless you create a function to do it:

(Toggle Plain Text)

def pc(x): return x / 100.0

gone = energy * pc(50)

Or

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pc = 0.01

gone = energy * 50*pc

The problem is that % is already the modulus operator, so it can't also be used for percentages.

ptmcg · Jan 30th, 2007, 10:52 AM

Python's ability to emulate numeric types makes it easy to "extend" Python with some interesting behavior. Here's a Percent class that allows you to write code like: saleprice = origprice - discount, where origprice is a number, and discount is a class instance that computes the actual discount based on the value of origprice.

You could do the same thing with a variable called markup as in markup=Percent(10) and then compute retailprice = wholesaleprice + markup.

-- Paul

(Toggle Plain Text)

class Percent(object):
    def __init__(self,pctval):
        self.pct = pctval
        self.pctFloat = pctval/100.0
        
    def __mul__(self,other):
        if isinstance(other,Percent):
            return Percent(self.pct*other.pctFloat)
        else:
            return other*self.pctFloat
            
    def __rmul__(self,other):
        return self * other

    def __radd__(self,other):
        if isinstance(other,Percent):
            return Percent(self.pct+other.pct)
        else:
            return other + self*other

    def __rsub__(self,other):
        if isinstance(other,Percent):
            return Percent(other.pct-self.pct)
        else:
            return other - self*other

    def __str__(self):
        if int(self.pct)==self.pct:
            return "%d%%" % self.pct
        else:
            return "%f%%" % self.pct

discount = Percent(20)
print discount

print 35 - discount
print 50 - discount
print 100 - discount

origprice = 35.00
saleprice = origprice - discount
print saleprice

Prints:

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20%
28.0
40.0
80.0
28.0

DaWei · Jan 30th, 2007, 1:32 PM

Very short.

ptmcg · Jan 30th, 2007, 6:55 PM

Well, once you get the class junk out of the way, I'd say this is pretty short/elegant, certainly more along the lines of what the OP was looking for.

(Toggle Plain Text)

discount = Percent(20)
origprice = 35.00
saleprice = origprice - discount

Percent is more than just a fancy wrapper around "divide by 100". Note that discount can be subtracted from any number of other values, and it will calculate the respective percentage before returning the value.

Are you the curmudgeon-in-residence on these forums?

-- Paul

DaWei · Jan 30th, 2007, 7:55 PM

If it makes me a curmudgeon to point out when you're being silly, yes, indeed. The OP distinctly asked for a short way. Merely hiding things so that they aren't visible at the point of invocation doesn't qualify as either short or elegant.

Game_Ender · Jan 31st, 2007, 3:41 AM

Isn't the point of invocation what matters? Or at least what matters in this case.

Jan 30th, 2007, 3:04 AM	#1
kurt Programmer Join Date: Oct 2005 Posts: 72 Rep Power: 4	Arithmetic By Percentage Let's say i want to perform a subtraction on a variable (say, Energy) by 5%, the shortest way i can think of is: (Toggle Plain Text) Tolerance = 0.05 * Energy Energy = Energy - Tolerance Tolerance = 0.05 * Energy Energy = Energy - Tolerance or (Toggle Plain Text) Energy = Energy - 0.05(Energy) Energy = Energy - 0.05(Energy) I know it's already pretty short, but is there a shorter, elegant way?

Jan 30th, 2007, 4:48 AM	#2
Arevos Programming Guru Join Date: Aug 2005 Location: England Posts: 1,499 Rep Power: 5	I think the shortest you could get would be: (Toggle Plain Text) energy -= 0.05 * energy energy -= 0.05 * energy Or: (Toggle Plain Text) energy = 0.95 energy = 0.95

Jan 30th, 2007, 5:15 AM	#4
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,254 Rep Power: 5	If I'm understanding you right ..... (Toggle Plain Text) gone = energypercentage; energy -= gone total_gone += gone gone = energypercentage; energy -= gone total_gone += gone

Jan 30th, 2007, 10:52 AM	#6
ptmcg Newbie Join Date: Aug 2005 Location: Austin, TX Posts: 15 Rep Power: 0	A Percent class for doing percentage arithmetic Python's ability to emulate numeric types makes it easy to "extend" Python with some interesting behavior. Here's a Percent class that allows you to write code like: saleprice = origprice - discount, where origprice is a number, and discount is a class instance that computes the actual discount based on the value of origprice. You could do the same thing with a variable called markup as in markup=Percent(10) and then compute retailprice = wholesaleprice + markup. -- Paul (Toggle Plain Text) class Percent(object): def __init__(self,pctval): self.pct = pctval self.pctFloat = pctval/100.0 def __mul__(self,other): if isinstance(other,Percent): return Percent(self.pctother.pctFloat) else: return otherself.pctFloat def __rmul__(self,other): return self * other def __radd__(self,other): if isinstance(other,Percent): return Percent(self.pct+other.pct) else: return other + selfother def __rsub__(self,other): if isinstance(other,Percent): return Percent(other.pct-self.pct) else: return other - selfother def __str__(self): if int(self.pct)==self.pct: return "%d%%" % self.pct else: return "%f%%" % self.pct discount = Percent(20) print discount print 35 - discount print 50 - discount print 100 - discount origprice = 35.00 saleprice = origprice - discount print saleprice class Percent(object): def __init__(self,pctval): self.pct = pctval self.pctFloat = pctval/100.0 def __mul__(self,other): if isinstance(other,Percent): return Percent(self.pctother.pctFloat) else: return otherself.pctFloat def __rmul__(self,other): return self * other def __radd__(self,other): if isinstance(other,Percent): return Percent(self.pct+other.pct) else: return other + selfother def __rsub__(self,other): if isinstance(other,Percent): return Percent(other.pct-self.pct) else: return other - selfother def __str__(self): if int(self.pct)==self.pct: return "%d%%" % self.pct else: return "%f%%" % self.pct discount = Percent(20) print discount print 35 - discount print 50 - discount print 100 - discount origprice = 35.00 saleprice = origprice - discount print saleprice Prints: (Toggle Plain Text) 20% 28.0 40.0 80.0 28.0 20% 28.0 40.0 80.0 28.0

Jan 30th, 2007, 1:32 PM	#7
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Very short. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Jan 30th, 2007, 4:59 AM	#3
kurt Programmer Join Date: Oct 2005 Posts: 72 Rep Power: 4	I was hoping there's something like: Gone = energy * 50%

Jan 30th, 2007, 6:55 PM	#8
ptmcg Newbie Join Date: Aug 2005 Location: Austin, TX Posts: 15 Rep Power: 0	Well, once you get the class junk out of the way, I'd say this is pretty short/elegant, certainly more along the lines of what the OP was looking for. (Toggle Plain Text) discount = Percent(20) origprice = 35.00 saleprice = origprice - discount discount = Percent(20) origprice = 35.00 saleprice = origprice - discount Percent is more than just a fancy wrapper around "divide by 100". Note that discount can be subtracted from any number of other values, and it will calculate the respective percentage before returning the value. Are you the curmudgeon-in-residence on these forums? -- Paul

Jan 30th, 2007, 7:55 PM	#9
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	If it makes me a curmudgeon to point out when you're being silly, yes, indeed. The OP distinctly asked for a short way. Merely hiding things so that they aren't visible at the point of invocation doesn't qualify as either short or elegant. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Jan 31st, 2007, 3:41 AM	#10
Game_Ender Professional Programmer Join Date: May 2006 Location: Maryland, USA Posts: 306 Rep Power: 3	Isn't the point of invocation what matters? Or at least what matters in this case. __________________ Robotics @ Maryland AUV Team - Software Lead

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Programming Forums > Script Programming > Python

Arithmetic By Percentage