How to determine prime numbers in python

How to judge prime numbers in python: first use python’s mathematical functions; then scan the prime numbers in a single line program, the code is [[ p for p in range(2, N) if 0 not in [ p% d for d in range(2,int(sqrt(p)].

The operating environment of this tutorial: windows7 system, python3.9 version, DELL G3 computer.

Python prime number judgment method:

1. Use python’s mathematical functions

import math 
 
def isPrime(n): 
  if n <= 1: 
  return False
  for i in range(2, int(math.sqrt(n)) + 1): 
  if n % i == 0: 
    return False
  return True

2. Single-line program to scan prime numbers

from math import sqrt 
N = 100
[ p for p in  range(2, N) if 0 not in [ p% d for d in range(2, int(sqrt(p))+1)] ]

Using python’s itertools module

from itertools import count 
def isPrime(n): www.jb51.net
  if n <= 1: 
    return False
  for i in count(2): 
    if i * i > n: 
      return True
    if n % i == 0: 
      return False

3. Two methods without using modules

Method 1:

def isPrime(n): 
  if n <= 1: 
    return False
  i = 2
  while i*i <= n: 
    if n % i == 0: 
      return False
    i += 1
  return True

Method 2:

def isPrime(n): 
  if n <= 1: 
    return False
  if n == 2: 
    return True
  if n % 2 == 0: 
    return False
  i = 3
  while i * i <= n: 
    if n % i == 0: 
      return False
    i += 2
  return True

eg: Find the prime number (prime number) between 20001 and 40001

Since it can only be digitized by 1 or by yourself, then It shows that only when the remainder is 0 twice, the code is as follows:

#!/usr/bin/python
 
L1=[]
for x in xrange(20001,40001):
 n = 0
 for y in xrange(1,x+1):
 if x % y == 0:
  n = n + 1
 if n == 2 :
 print x
 L1.append(x)
print L1

The result is as follows:

20011
20021
20023
20029
20047
20051
20063
20071
20089
20101
20107
20113
20117
20123
20129
20143
20147
20149
20161
20173
….

Related free learning recommendations: python video tutorial

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