Simple Nature - Light and Matter

calculator, but it’s a good way to design a programminglanguage so that names of functionsnever conflict.)Try it. Experiment and figure out whetherPython’s trig functions assume radians ordegrees.VariablesPython lets you define variables and assignvalues to them using an equals sign:>>> dwarfs=7>>> print(dwarfs)>>> print(dwarfs+3)710Note that a variable in computer programmingisn’t quite like a variable in algebra. Inalgebra, if a=7 then a=7 always, throughout aparticular calculation. But in a programminglanguage, the variable name really representsa place in memory where a number can bestored, so you can change its value:>>> dwarfs=7>>> dwarfs=37>>> print(dwarfs)37You can even do stuff like this,>>> dwarfs=37>>> dwarfs=dwarfs+1>>> print(dwarfs)38FunctionsSomebody had to teach Python how to dofunctions like sqrt, and it’s handy to be ableto define your own functions in the same way.Here’s how to do it:>>> def double(x):>>> return 2.*x>>> print(double(5.))10.0Note that the indentation is mandatory. Thefirst and second lines define a function calleddouble. The final line evaluates that functionwith an input of 5.LoopsSuppose we want to add up all the numbersfrom 0 to 99.Automating this kind of thing is exactlywhat computers are best at, and Python providesa mechanism for this called a loop:>>> sum=0>>> for j in range(100):>>> sum=sum+j>>> print(sum)4950The stuff that gets repeated — the inside ofthe loop — has to be indented, just like ina function definition. Python always countsloops starting from 0, so for j in range(100)actually causes j to range from 0 to 99, notfrom 1 to 100.In algebra it would be nonsense to have a variableequal to itself plus one, but in a computerprogram, it’s not an assertion that thetwo things are equal, its a command to calculatethe value of the expression on the rightside of the equals, and then put that numberinto the memory location referred to by thevariable name on the left.Try it. What happens if you do dwarfs+1 =dwarfs? Do you understand why?Exercises 909