素数函数从R到Python

Question

I wanted to rewrite my own "Prime numbers" fuction from R to Python. In R it looks like this:

 prime_numbers <- function(x)
   {
     p <- 2
     result <- NULL
     while (p <= x)
     {
        if (x<3) lp <- c(2) else if (x<5) lp <- c(2,3) else if (x<7) l<- c(2,3,5) else lp <- c(2,3,5,7)
        if (p%%2!=0 && p%%3!=0 && p%%5!=0 && p%%7!=0) result <- c(result,p)
        p <- p+1 
     }
     return(c(lp,result))
  }

It's working properly. I just have to set a number as a parameter and it prints all prime numbers smaller than this number.

I wrote this function in Python.

def prime_numbers (x):
   p = 2
   result = None
   while p <= x:
       if x<3:
           lp = 2
       elif x<5:
           lp = [2,3]
       elif x<7:
           lp = [2,3,5]
       else:
           lp = [2,3,5,7]
       if p%2!=0 and p%3!=0 and p%5!=0 and p%7!=0:
           result = [result,p]
       p = p+1
   return [lp,result]

The result is close to being proper, but I receive something like this in console when I use 50 for example as a parameter.

[[2, 3, 5, 7], [[[[[[[[[[[None, 11], 13], 17], 19], 23], 29], 31], 37], 41], 43], 47]]

None is printed and list is composed in a weird way to me. It seems to me as lists in Python are not as easy and flexible as vectors in R.

How can I get the same effect in Python as in R with using as much similar syntax as possible?

Answer 1

This should do it:

def prime_numbers(x):
   p = 2
   result = [] # instead of "result = None"
   while p <= x:
       if x<3:
           lp = 2
       elif x<5:
           lp = [2,3]
       elif x<7:
           lp = [2,3,5]
       else:
           lp = [2,3,5,7]
       if p%2!=0 and p%3!=0 and p%5!=0 and p%7!=0:
           result.append(p) # instead of "result = [result, p]"
       p = p+1
   return lp + result # instead of "[lp, result]"

>>> prime_numbers(50)
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

Like Professor_joykill mentioned, you should instantiate result as an empty list instead of as the value None.
Then use append(p) to add your prime number to the list of prime numbers > 7.
Lastly you concatenate your lists by using '+' instead of incorporating two lists into another list.

Hope this helps,
Koen