[Tutor] guess-my-number programme

[Kĩnũthia Mũchane]

On 09/23/2011 11:28 PM, Wayne Werner wrote:
> On Fri, Sep 23, 2011 at 2:25 PM, ADRIAN KELLY <kellyadrian at hotmail.com 
> <mailto:kellyadrian at hotmail.com>> wrote:
>
>     <snip>
>
>     can anyone explain the *_tries_* part of this programme to me i
>     know its meant to count the number of guesses made by the user by
>     adding 1 but i just cant figure out how it does this..........can
>     someone explain??  i.e. tries = 1, tries +1 etc.... cant get my
>     head around it...
>
>
> The concept that's confusing you here is something called order of 
> evaluation, or evaluation strategy: 
> http://en.wikipedia.org/wiki/Evaluation_strategy
>
> The best way to understand these things is to try it out, and the 
> interactive interpreter is extremely handy.
>
> I presume you understand the concept of assignment, correct? For example:
>
> >>> tries = 1
>
> Now tries contains 1:
>
> >>> tries = 1
> >>> tries
> 1
>
> The variable 'tries' now contains the value 1 (In Python this is not 
> technically true, but it's useful to describe it that way).
Why?
>
> >>> tries = 4
>
> Now 'tries' contains 4. Of course, just like your standard algebra 
> variables, you can use your variables in python:
>
> >>> tries * 4
> 16
> >>> tries + tries
> 8
> >>> tries / 1
> 4
>
> when these expressions are /evaluated/ they produce the mathematical 
> expression you probably expect. But you can do more than just evaluate 
> expressions, you can store their results:
>
> >>> lots_of_tries = tries * 100
> >>> lots_of_tries
> 400
>
> So what about the expression that confuses you?
>
> >>> tries = tries + 1
> >>> tries
> 5
>
> Well, the first thing that happens when python sees the equals sign is 
> that the right hand side of the expression is evaluated, so python takes:
>
>     tries = tries + 1
>
> and turns it into
>
>     tries = 4 + 1
>     tries = 5
>
> So each time your program sees 'tries = tries + 1' python evaluates 
> the right side first, then assigns its value to the variable on the left.
>
> HTH,
> Wayne
>
>
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