# `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 x16 + x12 + x5 + 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.