Base64 如何工作以及如何在其中进行编码/解码？

Question

I have a problem that asks me to encode a string to base64 format: I think I got it based on my code. The string: "Man" works and other short strings work. But the string. "this is a string:," doesn't work. And also I want to use the non-padding version, The questions asks me to use the non-padding version. Can you please explain the process of how to encode this string. "this is a string.,"! I have to turn the letters to ascii, and then turn them into binary and divide them into 6 bytes and then turn them to decimal and refer to a chart of ascii and then use them. This is all I know! But, please don't give me the code. I want to try out the coding on my own. But please explain the process. There are no good videos explaining this topic! And by the way, I am using python
Thank you

Here is the code I have:

def decimal(binary):
    binary = str(binary); power = len(binary)-1
    values = []

    for x in binary:
        if x == "1":
            values.append((x, 2**power))
        power -= 1
    
    return sum([v for b,v in values if b == "1"])


string = "Man"

byte = ""
for x in string:
    byte += bin(ord(x))[0] + bin(ord(x))[2:]


values = []
for x in range(0, len(byte), 6):
    values.append(byte[x:x+6])

abc = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

table = {x:abc[x] for x in range(len(abc))}
print("".join(table[decimal(x)] for x in values))

I am using python!

Answer 1

Adjusted parts are explained using in-line comments:

import sys   # merely for manipulation with supplied arguments 
import math 

if len(sys.argv) == 1:
    string = "This is a string!!!"
else:
    string = ' '.join([sys.argv[i] for i in range(1,len(sys.argv))])

def decimal(binary):
    binary = str(binary); power = len(binary)-1
    values = []
    for x in binary:
        if x == "1":
            values.append((x, 2**power))
        power -= 1
    return sum([v for b,v in values if b == "1"])

byte = ""
for x in string.encode('utf-8'):     # ASCII is a proper subset of UTF-8
    byte += bin(x)[2:].rjust(8,'0')  # get binary string of length 8

byte = byte.ljust(math.ceil(len(byte)/6)*6,'0') # length must be divisible by 6 

values = []
for x in range(0, len(byte), 6):
    values.append(byte[x:x+6])

abc = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
table = {x:abc[x] for x in range(len(abc))}

print(string)                                 # input
padding = '=' * (((3 - len(string.encode('utf-8'))) % 3) % 3)
ooutput = "".join(table[decimal(x)] for x in values)
print(ooutput)
print(ooutput + padding)                       # for the sake of completeness

import base64   # merely for comparison/reference output
                # ↓↓↓ output from base64 module ↓↓↓
print(base64.b64encode(string.encode('utf-8')).decode('utf-8'))  

Output : .\SO\66724448.py ěščř ĚŠČŘ &.\SO\66724448.py

ěščř ĚŠČŘ
xJvFocSNxZkgxJrFoMSMxZg
xJvFocSNxZkgxJrFoMSMxZg=
xJvFocSNxZkgxJrFoMSMxZg=
This is a string!!!
VGhpcyBpcyBhIHN0cmluZyEhIQ
VGhpcyBpcyBhIHN0cmluZyEhIQ==
VGhpcyBpcyBhIHN0cmluZyEhIQ==