Replace base64_cipher.py with an easy to understand version (#3925)

* rename base64_cipher.py to base64_encoding.py

* edit base64_encoding.py

* import necessary modules inside doctests

* make it behave like the official implementation

* replace format with f-string where possible

* replace format with f-string

Co-authored-by: Christian Clauss <cclauss@me.com>

* fix: syntax error due to closing parenthese

* reformat code

Co-authored-by: Christian Clauss <cclauss@me.com>

ciphers/base64_cipher.py

@@ -1,89 +0,0 @@
-def encode_base64(text: str) -> str:
-    r"""
-    >>> encode_base64('WELCOME to base64 encoding 😁')
-    'V0VMQ09NRSB0byBiYXNlNjQgZW5jb2Rpbmcg8J+YgQ=='
-    >>> encode_base64('AÅᐃ𐀏🤓')
-    'QcOF4ZCD8JCAj/CfpJM='
-    >>> encode_base64('A'*60)
-    'QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB\r\nQUFB'
-    """
-    base64_chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
-
-    byte_text = bytes(text, "utf-8")  # put text in bytes for unicode support
-    r = ""  # the result
-    c = -len(byte_text) % 3  # the length of padding
-    p = "=" * c  # the padding
-    s = byte_text + b"\x00" * c  # the text to encode
-
-    i = 0
-    while i < len(s):
-        if i > 0 and ((i / 3 * 4) % 76) == 0:
-            r = r + "\r\n"  # for unix newline, put "\n"
-
-        n = (s[i] << 16) + (s[i + 1] << 8) + s[i + 2]
-
-        n1 = (n >> 18) & 63
-        n2 = (n >> 12) & 63
-        n3 = (n >> 6) & 63
-        n4 = n & 63
-
-        r += base64_chars[n1] + base64_chars[n2] + base64_chars[n3] + base64_chars[n4]
-        i += 3
-
-    return r[0 : len(r) - len(p)] + p
-
-
-def decode_base64(text: str) -> str:
-    r"""
-    >>> decode_base64('V0VMQ09NRSB0byBiYXNlNjQgZW5jb2Rpbmcg8J+YgQ==')
-    'WELCOME to base64 encoding 😁'
-    >>> decode_base64('QcOF4ZCD8JCAj/CfpJM=')
-    'AÅᐃ𐀏🤓'
-    >>> decode_base64("QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUF"
-    ...               "BQUFBQUFBQUFB\r\nQUFB")
-    'AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA'
-    """
-    base64_chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
-    s = ""
-
-    for i in text:
-        if i in base64_chars:
-            s += i
-            c = ""
-        else:
-            if i == "=":
-                c += "="
-
-    p = ""
-    if c == "=":
-        p = "A"
-    else:
-        if c == "==":
-            p = "AA"
-
-    r = b""
-    s = s + p
-
-    i = 0
-    while i < len(s):
-        n = (
-            (base64_chars.index(s[i]) << 18)
-            + (base64_chars.index(s[i + 1]) << 12)
-            + (base64_chars.index(s[i + 2]) << 6)
-            + base64_chars.index(s[i + 3])
-        )
-
-        r += bytes([(n >> 16) & 255]) + bytes([(n >> 8) & 255]) + bytes([n & 255])
-
-        i += 4
-
-    return str(r[0 : len(r) - len(p)], "utf-8")
-
-
-def main():
-    print(encode_base64("WELCOME to base64 encoding 😁"))
-    print(decode_base64(encode_base64("WELCOME to base64 encoding 😁")))
-
-
-if __name__ == "__main__":
-    main()