1.for实现：

str1 = str.strip(input("please input a str:"))
n = 1
i = 0
for i in range(len(str1)-1):
    if str.isalnum(str1[i]) != str.isalnum(str1[i+1]):
        n += 1
    else:
        i += 1
print("字符个数为：",int((n+1)/2))

2.while实现：

# str1 = str.strip(input("please input a str:"))
# n = 0
# i = 0
# while i < len(str1):
#     while str1[i] != " ":
#         i += 1
#         if i == len(str1):
#             break
#     n += 1
#     if i == len(str1):
#         break
#     while str1[i] == " ":
#         i += 1
# print(n)

+++++++++++++++++++++++++++++++++++++++++++++++++++++

# str1 = str.strip(input("please input a str:"))
# n = 1
# i = 0
# while i < len(str1):
#     while str1[i] == ' ':
#         n += 1
#         i += 1
#         break
#     while str1[i] == ' ':
#         i += 1
#     i += 1
# print(n)