python字符的各种处理，不用内置函数总结

# e=input("输入自然数字字符串：")
# result=0
# for x in e:
#     result+=eval(x)-------------------第一题
# print(result)


# def rev(str):
#     print(str[-1::-1])

# if __name__ == ‘__main__‘:-----------------第二题
#     st=input()
#     rev(st)

# def max(*a):
#     m=a[0]
#     for x in a:
#         if x>m:
#             m=x
#     return m

# if __name__ == ‘__main__‘:------------------------第三题
#     e=eval(input())
#     result=max(*e)
#     print("最大值是：{}".format(result))

# a=[200,300,456,456]
# b=[]
# for i in range(len(a)):----------数字列表转换成字符串列表------第四题
#     b.append(str(a[i]))
# print(b)


# a=[234,354,‘a‘,None,False]
# b=[]
# for i in range(len(a)):
#     if(bool(a[i])==True):---------------bool字符判断--------第五题
#         b.append(a[i])
# print(b)

# def avg(*a):
#     result=0
#     n=0
#     for x in a:
#         result+=x
#         n+=1
#     avge=result/n
#     return avge

# if __name__ == ‘__main__‘:
#     e=eval(input(":"))
#     print("平均数为:{:.3f}".format(avg(*e)))------------------计算平均数-------第六题


# def sort(a):
#     str2=[]
#     max=a[0]
#     for i in range(len(a)):
#         for j in range(0,len(a)-i-1):
#             if a[j]<=a[j+1]:
#                 a[j],a[j+1]=a[j+1],a[j]
#     for x in range(len(a)):
#         str2.append(a[x])
#     print(str2)

# if __name__ == ‘__main__‘:
#     e=[23,34,435,78,21,32,23]----------------------降序排列----------第七题
#     sort(e)

# def index_sort(arr):
#     b=[]
#     for x in range(len(arr)):
#         index=len(str(arr[x]))
#         b.append(index)
#     print(b)

# if __name__ == ‘__main__‘:-----------------------输出位数-------------第八题
#     e=eval(input(":"))
#     index_sort(e)


# def num1(num):
#     if num>=0:
#         num=num
#     else:
#         num*=-1
#     return num

# def max_num1(arr):
#     max=arr[0]
#     for x in range(len(arr)):
#         if num1(arr[x])>=max:
#             max=arr[x]
#     print(max)

# if __name__ == ‘__main__‘:
#     e=eval(input("用于比较绝对值大小:"))-------------比较绝对值大小------第九题
#     max_num1(e)

# def hort(arr):
#     result=1
#     for x in range(len(arr)):
#         result*=arr[x]
#     print(result) 

# if __name__ == ‘__main__‘:--------------------列表数字相呈乘------第十题
#     e=eval(input())
#     hort(e)


# a=[1,2,3,4]
# b=[5,6,7,8]
# result=0
# for x in range(len(a)):
#     result+=(a[x]*b[x])--------------------向量内积-------------第十一题
# print(result)