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Conditional execution in Python is handled with the If statement.

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So, let's go ahead and make a working copy of conditionals.py, call it

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conditionals-working.py, and we'll Open that up and start by just defining a

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couple of variables.

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a and b equals 0 and 1.

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If we want to just execute some code, if a is less than b, all we do is we type if a < b:

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print ('this is true').

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Now, when I save that and run it, you see that 'this is true' got printed.

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So, this print statement executed, and the way this works is the if keyword

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introduces the conditional, and the expression here, a is less than b, and that

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could be any expression that evaluates to True or False and a colon introduces

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the suite of code and so this could be a suite of code.

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It could be a number of things, and that gets executed if this

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expression evaluates to true.

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If the expression does not evaluate to true - I'll just change this 0 to 1, and a

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is no longer less than b, save that and run it - then nothing happens at all.

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So, if we want something different to happen, if the expression is false, then I

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can simply say else and a colon and another suite of code, it is not True.

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So, if I save that and run it, then we get that here it is not true, and if I

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make this 1 a 0 again, save and run, then we get 'this is true.'

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So, this expression can actually be any expression that evaluates to true or

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false, and so I could just actually put the word True there, and it'll be true,

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save and run, this is true, or I can put the word False there, and save and run,

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and we get, 'it is not true.'

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So, that is the if and else in Python.

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If is a keyword, and then it's followed by any expression that evaluates true or

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false and a colon and then a suite of code, and the optional else will execute

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its suite of code, if the condition is false and not true.