A code poem.

serpentine.py

def serpentine(n_max):

    
    
#         \ /
#          Y
#          #
#          #
#         # 
#        #
#       #
#      ##
#    #####
#"""      #"""
##    V V    #
##    T T    #
##           #
##     *     #
##    =*=    #
#  #   *    #
#   #     #

    b = -1
    i = 1
    j = 0
    k = 0
    
    while True:
        
        if k <= 1:
            i = 1
            k += 1
            
        elif b >= n_max-1:
            
            if j == 1:
                i = -1
                j = 0
                
            else:
                j = 1
                i = 0
                
        elif b <= 0:
            
            if j == 1:
                i = 1
                j = 0
                
            else:
                j = 1
                i = 0

        b += i
        
        yield b

        
        #####
        ####
        ###
        ##
        #
    

s = serpentine(8)
[next(s) for _ in range(50)]

[0,
 1,
 2,
 3,
 4,
 5,
 6,
 7,
 7,
 6,
 5,
 4,
 3,
 2,
 1,
 0,
 0,
 1,
 2,
 3,
 4,
 5,
 6,
 7,
 7,
 6,
 5,
 4,
 3,
 2,
 1,
 0,
 0,
 1,
 2,
 3,
 4,
 5,
 6,
 7,
 7,
 6,
 5,
 4,
 3,
 2,
 1,
 0,
 0,
 1]