为什么切片[::1]与-1，对于代码的print完全不一样？

Question

# [::1]
# 方法一 切片
 def aiphabet_graphics(n,m):
     letter = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
     for i in range(n):
         res_1 = letter[1:i+1]
         res_2 = letter[0:m+1]
         res = res_1[::-1] + res_2
         print(res[0:m])
         pass
     pass
 n,m = map(int,input().split())
 aiphabet_graphics(n,m)
 # 方法二 循环
 n,m = map(int,input().split())
 if(n>=1 and m<=26):
     for i in range(n):
         k,t1,t2=i,0,1
         for j in range(m):
             if (k<=i and k>=0):
                 print(chr(65+i-t1),end='')
                 t1,k=t1+1,k-1
             else:
                 print(chr(65+t2),end='')
                 t2=t2+1
         print("")

# [::-1]

)""(tnirp
1+2t=2t
)''=dne,)2t+56(rhc(tnirp
:esle
1-k,1+1t=k,1t
)''=dne,)1t-i+56(rhc(tnirp
:)0=>k dna i=<k( fi
:)m(egnar ni j rof
1,0,i=2t,1t,k
:)n(egnar ni i rof
:)62=<m dna 1=>n(fi
))(tilps.)(tupni,tni(pam = m,n
环循 二法方 #
)m,n(scihparg_tebahpia
))(tilps.)(tupni,tni(pam = m,n
ssap
ssap
)]m:0[ser(tnirp
2_ser + ]1-::[1_ser = ser
]1+m:0[rettel = 2_ser
]1+i:1[rettel = 1_ser
:)n(egnar ni i rof
"ZYXWVUTSRQPONMLKJIHGFEDCBA" = rettel
:)m,n(scihparg_tebahpia fed
片切 一法方 #

# 随便回答吧

Answer 1

::-1是反向切片