"binascii" --- 在二進位制和 ASCII 之間轉換
******************************************

======================================================================

The "binascii" module contains a number of methods to convert between
binary and various ASCII-encoded binary representations. Normally, you
will not use these functions directly but use wrapper modules like
"base64" instead. The "binascii" module contains low-level functions
written in C for greater speed that are used by the higher-level
modules.

備註:

  "a2b_*" functions accept Unicode strings containing only ASCII
  characters. Other functions only accept *bytes-like objects* (such
  as "bytes", "bytearray" and other objects that support the buffer
  protocol).

  在 3.3 版的變更: ASCII-only unicode strings are now accepted by the
  "a2b_*" functions.

"binascii" 模組定義了以下函式：

binascii.a2b_uu(string)

   Convert a single line of uuencoded data back to binary and return
   the binary data. Lines normally contain 45 (binary) bytes, except
   for the last line. Line data may be followed by whitespace.

binascii.b2a_uu(data, *, backtick=False)

   Convert binary data to a line of ASCII characters, the return value
   is the converted line, including a newline char. The length of
   *data* should be at most 45. If *backtick* is true, zeros are
   represented by "'`'" instead of spaces.

   在 3.7 版的變更: 新增 *backtick* 參數。

binascii.a2b_base64(string, /, *, padded=True, alphabet=BASE64_ALPHABET, strict_mode=False, canonical=False)
binascii.a2b_base64(string, /, *, ignorechars, padded=True, alphabet=BASE64_ALPHABET, strict_mode=True, canonical=False)

   Convert a block of base64 data back to binary and return the binary
   data. More than one line may be passed at a time.

   Optional *alphabet* must be a "bytes" object of length 64 which
   specifies an alternative alphabet.

   If *padded* is true, the last group of 4 base 64 alphabet
   characters must be padded with the '=' character. If *padded* is
   false, padding is neither required nor recognized: the '='
   character is not treated as padding but as a non-alphabet
   character, which means it is silently discarded when *strict_mode*
   is false, or causes an "Error" when *strict_mode* is true unless
   b'=' is included in *ignorechars*.

   If *ignorechars* is specified, it should be a *bytes-like object*
   containing characters to ignore from the input when *strict_mode*
   is true. If *ignorechars* contains the pad character "'='",  the
   pad characters presented before the end of the encoded data and the
   excess pad characters will be ignored. The default value of
   *strict_mode* is "True" if *ignorechars* is specified, "False"
   otherwise.

   If *strict_mode* is true, only valid base64 data will be converted.
   Invalid base64 data will raise "binascii.Error".

   Valid base64:

   * Conforms to **RFC 4648**.

   * Contains only characters from the base64 alphabet.

   * Contains no excess data after padding (including excess padding,
     newlines, etc.).

   * Does not start with a padding.

   If *canonical* is true, non-zero padding bits in the last group are
   rejected with "binascii.Error", enforcing canonical encoding as
   defined in **RFC 4648** section 3.5.  This check is independent of
   *strict_mode*.

   在 3.11 版的變更: 新增 *strict_mode* 參數。

   在 3.15 版的變更: Added the *alphabet*, *canonical*, *ignorechars*,
   and *padded* parameters.

binascii.b2a_base64(data, *, padded=True, alphabet=BASE64_ALPHABET, wrapcol=0, newline=True)

   Convert binary data to a line(s) of ASCII characters in base64
   coding, as specified in **RFC 4648**.

   If *padded* is true (default), pad the encoded data with the '='
   character to a size multiple of 4. If *padded* is false, do not add
   the pad characters.

   If *wrapcol* is non-zero, insert a newline ("b'\n'") character
   after at most every *wrapcol* characters. If *wrapcol* is zero
   (default), do not insert any newlines.

   If *newline* is true (default), a newline character will be added
   at the end of the output.

   在 3.6 版的變更: 新增 *newline* 參數。

   在 3.15 版的變更: Added the *alphabet*, *padded* and *wrapcol*
   parameters.

binascii.a2b_ascii85(string, /, *, foldspaces=False, adobe=False, ignorechars=b'', canonical=False)

   Convert Ascii85 data back to binary and return the binary data.

   Valid Ascii85 data contains characters from the Ascii85 alphabet in
   groups of five (except for the final group, which may have from two
   to five characters). Each group encodes 32 bits of binary data in
   the range from "0" to "2 ** 32 - 1", inclusive. The special
   character "z" is accepted as a short form of the group "!!!!!",
   which encodes four consecutive null bytes. A single-character final
   group is always rejected as an encoding violation.

   *foldspaces* is a flag that specifies whether the 'y' short
   sequence should be accepted as shorthand for 4 consecutive spaces
   (ASCII 0x20). This feature is not supported by the "standard"
   Ascii85 encoding.

   *adobe* controls whether the encoded byte sequence is framed with
   "<~" and "~>", as in a PostScript base-85 string literal.  If
   *adobe* is true, a leading "<~" is optionally accepted, while a
   trailing "~>" is *required*, and "binascii.Error" is raised if it
   is not found.

   *ignorechars* should be a *bytes-like object* containing characters
   to ignore from the input. This should only contain whitespace
   characters.

   If *canonical* is true, non-canonical encodings are rejected with
   "binascii.Error".  Here "canonical" means the encoding that
   "b2a_ascii85()" would produce: the "z" abbreviation must be used
   for all-zero groups (rather than "!!!!!"), and partial final groups
   must use the same padding digits as the encoder.

   Invalid Ascii85 data will raise "binascii.Error".

   在 3.15 版被加入.

binascii.b2a_ascii85(data, /, *, foldspaces=False, wrapcol=0, pad=False, adobe=False)

   Convert binary data to a formatted sequence of ASCII characters in
   Ascii85 coding. The return value is the converted data.

   *foldspaces* is an optional flag that uses the special short
   sequence 'y' instead of 4 consecutive spaces (ASCII 0x20) as
   supported by 'btoa'. This feature is not supported by the
   "standard" Ascii85 encoding.

   If *wrapcol* is non-zero, insert a newline ("b'\n'") character
   after at most every *wrapcol* characters. If *wrapcol* is zero
   (default), do not insert any newlines.

   If *pad* is true, the zero-padding applied to the end of the input
   is fully retained in the output encoding, as done by "btoa",
   producing an exact multiple of 5 bytes of output. This is not part
   of the standard encoding used in PDF, as it does not preserve the
   length of the data.

   *adobe* controls whether the encoded byte sequence is framed with
   "<~" and "~>", as in a PostScript base-85 string literal.  Note
   that while ASCII85Decode streams in PDF documents *must* be
   terminated with "~>", they *must not* use a leading "<~".

   在 3.15 版被加入.

binascii.a2b_base85(string, /, *, alphabet=BASE85_ALPHABET, ignorechars=b'', canonical=False)

   Convert Base85 data back to binary and return the binary data. More
   than one line may be passed at a time.

   Valid Base85 data contains characters from the Base85 alphabet in
   groups of five (except for the final group, which may have from two
   to five characters). Each group encodes 32 bits of binary data in
   the range from "0" to "2 ** 32 - 1", inclusive. A single-character
   final group is always rejected as an encoding violation.

   Optional *alphabet* must be a "bytes" object of length 85 which
   specifies an alternative alphabet.

   *ignorechars* should be a *bytes-like object* containing characters
   to ignore from the input.

   If *canonical* is true, non-canonical encodings are rejected with
   "binascii.Error".  Here "canonical" means the encoding that
   "b2a_base85()" would produce: partial final groups must use the
   same padding digits as the encoder.

   Invalid Base85 data will raise "binascii.Error".

   在 3.15 版被加入.

binascii.b2a_base85(data, /, *, alphabet=BASE85_ALPHABET, wrapcol=0, pad=False)

   Convert binary data to a line of ASCII characters in Base85 coding.
   The return value is the converted line.

   Optional *alphabet* must be a *bytes-like object* of length 85
   which specifies an alternative alphabet.

   If *wrapcol* is non-zero, insert a newline ("b'\n'") character
   after at most every *wrapcol* characters. If *wrapcol* is zero
   (default), do not insert any newlines.

   If *pad* is true, the zero-padding applied to the end of the input
   is retained in the output, which will always be a multiple of 5
   bytes, and thus the length of the data may not be preserved on
   decoding.

   在 3.15 版被加入.

binascii.a2b_base32(string, /, *, padded=True, alphabet=BASE32_ALPHABET, ignorechars=b'', canonical=False)

   Convert base32 data back to binary and return the binary data.

   Valid base32 data contains characters from the base32 alphabet
   specified in **RFC 4648** in groups of eight (if necessary, the
   final group is padded to eight characters with "="). Each group
   encodes 40 bits of binary data in the range from "0" to "2 ** 40 -
   1", inclusive.

   備註:

     This function does not map lowercase characters (which are
     invalid in standard base32) to their uppercase counterparts, nor
     does it contextually map "0" to "O" and "1" to "I"/"L" as **RFC
     4648** allows.

   Optional *alphabet* must be a "bytes" object of length 32 which
   specifies an alternative alphabet.

   If *padded* is true, the last group of 8 base 32 alphabet
   characters must be padded with the '=' character. If *padded* is
   false, the '=' character is treated as other non-alphabet
   characters (depending on the value of *ignorechars*).

   *ignorechars* should be a *bytes-like object* containing characters
   to ignore from the input. If *ignorechars* contains the pad
   character "'='",  the pad characters presented before the end of
   the encoded data and the excess pad characters will be ignored.

   If *canonical* is true, non-zero padding bits in the last group are
   rejected with "binascii.Error", enforcing canonical encoding as
   defined in **RFC 4648** section 3.5.

   Invalid base32 data will raise "binascii.Error".

   在 3.15 版被加入.

binascii.b2a_base32(data, /, *, padded=True, alphabet=BASE32_ALPHABET, wrapcol=0)

   Convert binary data to a line of ASCII characters in base32 coding,
   as specified in **RFC 4648**. The return value is the converted
   line.

   Optional *alphabet* must be a *bytes-like object* of length 32
   which specifies an alternative alphabet.

   If *padded* is true (default), pad the encoded data with the '='
   character to a size multiple of 8. If *padded* is false, do not add
   the pad characters.

   If *wrapcol* is non-zero, insert a newline ("b'\n'") character
   after at most every *wrapcol* characters. If *wrapcol* is zero
   (default), do not insert any newlines.

   在 3.15 版被加入.

binascii.a2b_qp(data, header=False)

   Convert a block of quoted-printable data back to binary and return
   the binary data. More than one line may be passed at a time. If the
   optional argument *header* is present and true, underscores will be
   decoded as spaces.

binascii.b2a_qp(data, quotetabs=False, istext=True, header=False)

   Convert binary data to a line(s) of ASCII characters in quoted-
   printable encoding.  The return value is the converted line(s). If
   the optional argument *quotetabs* is present and true, all tabs and
   spaces will be encoded.   If the optional argument *istext* is
   present and true, newlines are not encoded but trailing whitespace
   will be encoded. If the optional argument *header* is present and
   true, spaces will be encoded as underscores per **RFC 1522**. If
   the optional argument *header* is present and false, newline
   characters will be encoded as well; otherwise linefeed conversion
   might corrupt the binary data stream.

binascii.crc_hqx(data, value)

   Compute a 16-bit CRC value of *data*, starting with *value* as the
   initial CRC, and return the result.  This uses the CRC-CCITT
   polynomial *x*^16 + *x*^12 + *x*^5 + 1, often represented as
   0x1021.  This CRC is used in the binhex4 format.

binascii.crc32(data[, value])

   Compute CRC-32, the unsigned 32-bit checksum of *data*, starting
   with an initial CRC of *value*.  The default initial CRC is zero.
   The algorithm is consistent with the ZIP file checksum.  Since the
   algorithm is designed for use as a checksum algorithm, it is not
   suitable for use as a general hash algorithm.  Use as follows:

      print(binascii.crc32(b"hello world"))
      # Or, in two pieces:
      crc = binascii.crc32(b"hello")
      crc = binascii.crc32(b" world", crc)
      print('crc32 = {:#010x}'.format(crc))

   在 3.0 版的變更: The result is always unsigned.

binascii.b2a_hex(data[, sep[, bytes_per_sep=1]])
binascii.hexlify(data[, sep[, bytes_per_sep=1]])

   Return the hexadecimal representation of the binary *data*.  Every
   byte of *data* is converted into the corresponding 2-digit hex
   representation.  The returned bytes object is therefore twice as
   long as the length of *data*.

   Similar functionality (but returning a text string) is also
   conveniently accessible using the "bytes.hex()" method.

   If *sep* is specified, it must be a single character str or bytes
   object. It will be inserted in the output after every
   *bytes_per_sep* input bytes. Separator placement is counted from
   the right end of the output by default, if you wish to count from
   the left, supply a negative *bytes_per_sep* value.

   >>> import binascii
   >>> binascii.b2a_hex(b'\xb9\x01\xef')
   b'b901ef'
   >>> binascii.hexlify(b'\xb9\x01\xef', '-')
   b'b9-01-ef'
   >>> binascii.b2a_hex(b'\xb9\x01\xef', b'_', 2)
   b'b9_01ef'
   >>> binascii.b2a_hex(b'\xb9\x01\xef', b' ', -2)
   b'b901 ef'

   在 3.8 版的變更: 新增 *sep* 與 *bytes_per_sep* 參數。

binascii.a2b_hex(hexstr, *, ignorechars=b'')
binascii.unhexlify(hexstr, *, ignorechars=b'')

   Return the binary data represented by the hexadecimal string
   *hexstr*.  This function is the inverse of "b2a_hex()". *hexstr*
   must contain an even number of hexadecimal digits (which can be
   upper or lower case), otherwise an "Error" exception is raised.

   *ignorechars* should be a *bytes-like object* containing characters
   to ignore from the input.

   Similar functionality (accepting only text string arguments, but
   more liberal towards whitespace) is also accessible using the
   "bytes.fromhex()" class method.

   在 3.15 版的變更: Added the *ignorechars* parameter.

exception binascii.Error

   Exception raised on errors. These are usually programming errors.

exception binascii.Incomplete

   Exception raised on incomplete data. These are usually not
   programming errors, but may be handled by reading a little more
   data and trying again.

binascii.BASE64_ALPHABET

   The Base 64 alphabet according to **RFC 4648**.

   在 3.15 版被加入.

binascii.URLSAFE_BASE64_ALPHABET

   The "URL and filename safe" Base 64 alphabet according to **RFC
   4648**.

   在 3.15 版被加入.

binascii.UU_ALPHABET

   The uuencoding alphabet.

   在 3.15 版被加入.

binascii.CRYPT_ALPHABET

   The Base 64 alphabet used in the *crypt(3)* routine and in the
   GEDCOM format.

   在 3.15 版被加入.

binascii.BINHEX_ALPHABET

   The Base 64 alphabet used in BinHex 4 (HQX) within the classic Mac
   OS.

   在 3.15 版被加入.

binascii.BASE85_ALPHABET

   The Base85 alphabet.

   在 3.15 版被加入.

binascii.ASCII85_ALPHABET

   The Ascii85 alphabet.

   在 3.15 版被加入.

binascii.Z85_ALPHABET

   The Z85 alphabet.

   在 3.15 版被加入.

binascii.BASE32_ALPHABET

   The Base 32 alphabet according to **RFC 4648**.

   在 3.15 版被加入.

binascii.BASE32HEX_ALPHABET

   The "Extended Hex" Base 32 alphabet according to **RFC 4648**. Data
   encoded with this alphabet maintains its sort order during bitwise
   comparisons.

   在 3.15 版被加入.

也參考:

  "base64" 模組
     Support for RFC compliant base64-style encoding in base 16, 32,
     64, and 85.

  "quopri" 模組
     Support for quoted-printable encoding used in MIME email
     messages.
