Question

Someone please help me understand how this returns what it returns. The process. I kinda get the first part how variable which is 0 divided by 4 returns 0. but how come it doesnt show 0 for the second if statement and prints 4 first, then 4 then 12 then 16
for variable in range(20):
if variable % 4 == 0:
print variable
if variable % 16 == 0:
print ('foo!')

Answer 1

From http://docs.python.org/2/reference/expressions.html :

"The % (modulo) operator yields the remainder from the division of the first argument by the second. The numeric arguments are first converted to a common type. A zero right argument raises the ZeroDivisionError exception. The arguments may be floating point numbers, e.g., 3.14%0.7 equals 0.34 (since 3.14 equals 4*0.7 + 0.34.) The modulo operator always yields a result with the same sign as its second operand (or zero); the absolute value of the result is strictly smaller than the absolute value of the second operand [2]."

Now let's examine your programs output:

0 // 0 % 4 == 0
foo! // 0 % 16 == 0
4 // 4 % 4 = 0
8 // 8 % 4 == 0
12 // 12 % 4 == 0
16 // 16 % 4 == 0
foo! // 16 % 16 == 0

Which is indeed correct.

The second statement, where variable has a value of 1, does not print any statements because both conditions fail:

1 / 4 == 0.25
1 / 16 == 0.0625

Does this make sense?

Answer 2

somewhat...the picture is a little clearer. I read your definition and understand somewhat. Do you think you can make your response more plain (python for dummies). I made the connection with the first 2 lines of output but the rest I still dont.

Answer 3

Have you tried calculating the third iteration of your loop by hand?

So, you need to evaluate the statement:

(2 % 4) == 0


In certain cases such as this, when you are working with a new operator it can be a good idea to create a test program. In this case you might want to calculate n % 4, given some value of n. This allows you to test your understanding and assumptions.

Answer 4

Something like,

for variable in range(20):
print str(variable) + ' % 4 = ' + str(variable % 4)
print str(variable) + ' % 16 = ' + str(variable % 16)
print '\n'

for example.

Answer 5

Ok after running your example and studying it, I have a better understanding. Thanks for your help.