python - 从字符串转换为 base-64 中的数字

Question

因此，我正在尝试编写一个程序来解码 6 个字符的 base-64 数字。

这里是问题陈述:

Return the 36-bit number represented as a base-64 number in reverse order by the 6-character string s where the order of the 64 numerals is: 0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-+

即

decode('000000') → 0

decode('gR1iC9') → 9876543210

decode('++++++') → 68719476735

我想在没有字符串的情况下执行此操作。

最简单的方法是创建以下函数的反函数:

def get_digit(d):
    ''' Convert a base 64 digit to the desired character '''
    if 0 <= d <= 9:
        # 0 - 9
        c = 48 + d
    elif 10 <= d <= 35:
        # A - Z
        c = 55 + d
    elif 36 <= d <= 61:
        # a - z
        c = 61 + d
    elif d == 62:
        # -
        c = 45
    elif d == 63:
        # +
        c = 43
    else:
        # We should never get here
        raise ValueError('Invalid digit for base 64: ' + str(d)) 
    return chr(c)

# Test `digit`
print(''.join([get_digit(d) for d in range(64)]))

def encode(n):
    ''' Convert integer n to base 64 '''
    out = []
    while n:
        n, r = n // 64, n % 64
        out.append(get_digit(r))
    while len(out) < 6:
        out.append('0')
    return ''.join(out)

# Test `encode`
for i in (0, 9876543210, 68719476735):
    print(i, encode(i))

输出

0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-+
0 000000
9876543210 gR1iC9
68719476735 ++++++

实际上来自 this 页面上的 PM 2Ring。

如何编写该程序的反函数？

开始:

get_digits 的逆运算如下:

def inv_get_digit(c):

    if 0 <= c <= 9:
        d = ord(c) - 48
    elif 'A' <= c <= 'Z':
        d = ord(c) - 55
    elif 'a' <= c <= 'z'
        d = ord(c) - 61
    elif c == '+':
        d = 63
    elif c == '-':
        d = 62
    else:
        raise ValueError('Invalid Input' + str(c))
    return d


def decode(n):

    out = []
    while n:
        n, r= n % 10, n ** (6-len(str))
        out.append(get_digit(r))
    while len(out) < 10:
        out.append('0')
    return ''.join(out)

Answer 1

这是一个将 my old code 与一些新代码结合起来执行逆运算的程序。

inv_get_digit 函数中存在语法错误:您在 elif 行末尾遗漏了冒号。并且不需要执行 str(c)，因为 c 已经是一个字符串。

恐怕您的decode 函数没有多大意义。它应该将字符串作为输入并返回一个整数。请查看下面的工作版本。

def get_digit(d):
    ''' Convert a base 64 digit to the desired character '''
    if 0 <= d <= 9:
        # 0 - 9
        c = 48 + d
    elif 10 <= d <= 35:
        # A - Z
        c = 55 + d
    elif 36 <= d <= 61:
        # a - z
        c = 61 + d
    elif d == 62:
        # -
        c = 45
    elif d == 63:
        # +
        c = 43
    else:
        # We should never get here
        raise ValueError('Invalid digit for base 64: ' + str(d)) 
    return chr(c)

print('Testing get_digit') 
digits = ''.join([get_digit(d) for d in range(64)])
print(digits)

def inv_get_digit(c):
    if '0' <= c <= '9':
        d = ord(c) - 48
    elif 'A' <= c <= 'Z':
        d = ord(c) - 55
    elif 'a' <= c <= 'z':
        d = ord(c) - 61
    elif c == '-':
        d = 62
    elif c == '+':
        d = 63
    else:
        raise ValueError('Invalid input: ' + c)
    return d

print('\nTesting inv_get_digit') 
nums = [inv_get_digit(c) for c in digits]
print(nums == list(range(64)))

def encode(n):
    ''' Convert integer n to base 64 '''
    out = []
    while n:
        n, r = n // 64, n % 64
        out.append(get_digit(r))
    while len(out) < 6:
        out.append('0')
    return ''.join(out)

print('\nTesting encode')
numdata = (0, 9876543210, 68719476735)
strdata = []
for i in numdata:
    s = encode(i)
    print(i, s)
    strdata.append(s)

def decode(s):
    out = []
    n = 0
    for c in reversed(s):
        d = inv_get_digit(c)
        n = 64 * n + d
    return n

print('\nTesting decode')
for s, oldn in zip(strdata, numdata):
    n = decode(s)
    print(s, n, n == oldn)

输出

Testing get_digit
0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-+

Testing inv_get_digit
True

Testing encode
0 000000
9876543210 gR1iC9
68719476735 ++++++

Testing decode
000000 0 True
gR1iC9 9876543210 True
++++++ 68719476735 True