Project Euler Problem 37 solution

"""
Problem 37 on project Euler
https://projecteuler.net/problem=37
"""
"""
Note: This code takes about 2 seconds to execute. You ca reduce this time by adapting to 
faster methods of checking if a number is prime or not like the Seive method.
But this code is intended to be beginner friendly so I have used the simple way to check for primes.
"""


def isprime(n):                 # checking if prime
    if n==1:
        return False
    if n!=2 and n%2==0:
        return False
    for i in range(3,int(math.sqrt(n)+1),2):
        if n%i==0:
            return False
    return True

def truncated(n):             # returns a list of truncated n 
    s = str(n)
    l = []
    l.append(int(s[:]))
    for i in range(1,len(s)):
        l.append(int(s[i:]))
        l.append(int(s[:-i]))
    return l    
    
    
primes =[]                    # generating a list of 2 digit primes                            
for i in range(100,1000):       # to validate the numbers so 
    if isprime(i):            #loop will check only a few numbers
        primes.append(str(i))
 """
 You can significantly reduce the numbers which you will ceheck by the following approach.
 A number will be truncatable prime iff the first and last two digits of the number are also prime.
 So I wrote a function "validate" which checks for the same and also if the first and last digit of a number is prime or not.
 This shall reduce the numbers that we will check and thus optimize the code a lot.
 """
        
def validate(n):                 # if the first two or last two digits of 
    if len(str(n))>3:            # n are not prime we will not check it
        if  str(n)[-3:] not in primes:
            return False
        if str(n)[:3] not in primes:
            return False
        if int(str(n)[-1])%2==0:         #if first digit of  
            return False                 # n is even we will not check it
    return True    
        
a=time.time()
c=0 #count variable
s=0  #sum
i=11
while c!=11:
    if validate(i):    
        l=truncated(i)
        l1 = list(map(isprime,l))
        if all(l1):
            print(i)
            s+=i
            c+=1
        
    i+=2
print("sum = ",s)    
print(time.time()-a)    
#sum=748317
#time = 2.1 seconds