if: must be followed by ':' and will note include '()', unlike C/C++.

for C/C++ programmer: while could be followed by an else sentense, when will it excute? when the while-condition is false, the while - else judgement will run to the else sentense to excute.(unlike the C/C++)

range(1,5) means [1, 2, 3, 4, 5), that is [1, 2, 3, 4](doesn't include the end number) it represents an array of numbers.

Note that we could assign an steplength to it using range(1,5,2),which means[1,3] that the third number is the steplength.