python not used int () function to convert a string of digital

Several methods of conversion are not included here symbol '-', spaces, and other numbers not letters, not including the decimal point, on Leetcode Question 8 including these. The method herein is only applicable to similar to '12356' into a digital 12356.

Method 1: Use the function str

Int function can not be used, we can identify with 0-9 str function of each digital representation of characters

def atoi(s):
    s = s[::1]   # 将s反转
    num=0
    for i,v in enumerate(s):
        for j in range(0,10):
            if v ==str(j):
                num+=j*(10**i)
    return num

Method 2: Using ord function

Using the ord function to find the ASCII code for each character in the ASCII code minus 0 is determined for each bit of digital

print (words ( ' 1 ' ))    # 49 
print (words ( ' 0 ' ))    # 48

def atoi2(s):
    s = s[::1]
    num = 0
    for i,v in enumerate(s):
        num+=(ord(v)-ord('0'))*(10**i)
    return num

Method three: eval function using

Function eval function is to serve as a valid string str evaluate expressions and return the results. Every character configured using the expression 1 multiplied and then converted to digital eval function to obtain a number for each character.

def atoi3(s):
    s = s[::1]
    num = 0
    for i,v in enumerate(s):
        t = '%s *1'%v
        n = eval(t)
        num+=n*(10**i)
    return num