On Fri, Sep 23, 2011 at 2:25 PM, ADRIAN KELLY <kellyadr...@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). >>> 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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