*= operator

[Cai Gengyang]

>>> bill = 100
>>> bill *= 1.08
>>> bill
108.0
>>> 




On Saturday, November 21, 2015 at 9:47:29 PM UTC+8, Frank Millman wrote:
> "Cai Gengyang"  wrote in message 
> news:a76b1b5b-4321-41bb-aeca-0dac787752d9 at googlegroups.com...
> 
> > This is a piece of code that calculates tax and tip :
> >
> > def tax(bill):
> >     """Adds 8% tax to a restaurant bill."""
> >     bill *= 1.08
> >     print "With tax: %f" % bill
> >     return bill
> >
> > def tip(bill):
> >     """Adds 15% tip to a restaurant bill."""
> >     bill *= 1.15
> >     print "With tip: %f" % bill
> >     return bill
> >
> > meal_cost = 100
> > meal_with_tax = tax(meal_cost)
> > meal_with_tip = tip(meal_with_tax)
> >
> > Does bill *= 1.08 mean bill = bill * 1.15 ?
> 
> Firstly, I assume that you actually meant 'bill = bill * 1.08' at the end of 
> the last line.
> 
> Secondly, how can I help you to answer this kind of question yourself.
> 
> Here are two ways.
> 
> 1. Try it out at the interpreter -
> 
> c:\>
> Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 24 2015, 22:44:40) [MSC v.1600 64 bit 
> (AMD64)] on win32
> Type "help", "copyright", "credits" or "license" for more information.
> >>> bill = 100
> >>> bill *= 1.08
> >>> bill
> 
> I deliberately omitted the last line. Try it yourself and see what you get.
> 
> 2. Read the fine manual.
> 
> The Index has a section headed 'Symbols'. From there you will find '*=', 
> with a link to 'augmented assignment'.
> 
> If you follow the link, you will find a detailed explanation. Here is an 
> excerpt -
> 
> "An augmented assignment expression like x += 1 can be rewritten as x = x + 
> 1 to achieve a similar, but not exactly equal effect. In the augmented 
> version, x is only evaluated once. Also, when possible, the actual operation 
> is performed in-place, meaning that rather than creating a new object and 
> assigning that to the target, the old object is modified instead."
> 
> Frank Millman