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Re: *= operator

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"Cai Gengyang"  wrote in message 
news:a76b1b5b-4321-41bb-aeca-0dac787752d9@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

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Thread

*= operator Cai Gengyang <gengyangcai@gmail.com> - 2015-11-21 05:20 -0800
  Re: *= operator BartC <bc@freeuk.com> - 2015-11-21 13:37 +0000
  Re: *= operator Steven D'Aprano <steve@pearwood.info> - 2015-11-22 00:39 +1100
    Re: *= operator Joel Goldstick <joel.goldstick@gmail.com> - 2015-11-21 08:58 -0500
  Re: *= operator "Frank Millman" <frank@chagford.com> - 2015-11-21 15:46 +0200
    Re: *= operator Cai Gengyang <gengyangcai@gmail.com> - 2015-11-21 05:55 -0800

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