1 :mod:`base64` --- Base16, Base32, Base64, Base85 Data Encodings 2 =============================================================== 3 4 .. module:: base64 5 :synopsis: RFC 3548: Base16, Base32, Base64 Data Encodings; 6 Base85 and Ascii85 7 8 **Source code:** :source:`Lib/base64.py` 9 10 .. index:: 11 pair: base64; encoding 12 single: MIME; base64 encoding 13 14 -------------- 15 16 This module provides functions for encoding binary data to printable 17 ASCII characters and decoding such encodings back to binary data. 18 It provides encoding and decoding functions for the encodings specified in 19 :rfc:`3548`, which defines the Base16, Base32, and Base64 algorithms, 20 and for the de-facto standard Ascii85 and Base85 encodings. 21 22 The :rfc:`3548` encodings are suitable for encoding binary data so that it can 23 safely sent by email, used as parts of URLs, or included as part of an HTTP 24 POST request. The encoding algorithm is not the same as the 25 :program:`uuencode` program. 26 27 There are two interfaces provided by this module. The modern interface 28 supports encoding :term:`bytes-like objects <bytes-like object>` to ASCII 29 :class:`bytes`, and decoding :term:`bytes-like objects <bytes-like object>` or 30 strings containing ASCII to :class:`bytes`. Both base-64 alphabets 31 defined in :rfc:`3548` (normal, and URL- and filesystem-safe) are supported. 32 33 The legacy interface does not support decoding from strings, but it does 34 provide functions for encoding and decoding to and from :term:`file objects 35 <file object>`. It only supports the Base64 standard alphabet, and it adds 36 newlines every 76 characters as per :rfc:`2045`. Note that if you are looking 37 for :rfc:`2045` support you probably want to be looking at the :mod:`email` 38 package instead. 39 40 41 .. versionchanged:: 3.3 42 ASCII-only Unicode strings are now accepted by the decoding functions of 43 the modern interface. 44 45 .. versionchanged:: 3.4 46 Any :term:`bytes-like objects <bytes-like object>` are now accepted by all 47 encoding and decoding functions in this module. Ascii85/Base85 support added. 48 49 The modern interface provides: 50 51 .. function:: b64encode(s, altchars=None) 52 53 Encode the :term:`bytes-like object` *s* using Base64 and return the encoded 54 :class:`bytes`. 55 56 Optional *altchars* must be a :term:`bytes-like object` of at least 57 length 2 (additional characters are ignored) which specifies an alternative 58 alphabet for the ``+`` and ``/`` characters. This allows an application to e.g. 59 generate URL or filesystem safe Base64 strings. The default is ``None``, for 60 which the standard Base64 alphabet is used. 61 62 63 .. function:: b64decode(s, altchars=None, validate=False) 64 65 Decode the Base64 encoded :term:`bytes-like object` or ASCII string 66 *s* and return the decoded :class:`bytes`. 67 68 Optional *altchars* must be a :term:`bytes-like object` or ASCII string of 69 at least length 2 (additional characters are ignored) which specifies the 70 alternative alphabet used instead of the ``+`` and ``/`` characters. 71 72 A :exc:`binascii.Error` exception is raised 73 if *s* is incorrectly padded. 74 75 If *validate* is ``False`` (the default), characters that are neither 76 in the normal base-64 alphabet nor the alternative alphabet are 77 discarded prior to the padding check. If *validate* is ``True``, 78 these non-alphabet characters in the input result in a 79 :exc:`binascii.Error`. 80 81 82 .. function:: standard_b64encode(s) 83 84 Encode :term:`bytes-like object` *s* using the standard Base64 alphabet 85 and return the encoded :class:`bytes`. 86 87 88 .. function:: standard_b64decode(s) 89 90 Decode :term:`bytes-like object` or ASCII string *s* using the standard 91 Base64 alphabet and return the decoded :class:`bytes`. 92 93 94 .. function:: urlsafe_b64encode(s) 95 96 Encode :term:`bytes-like object` *s* using the 97 URL- and filesystem-safe alphabet, which 98 substitutes ``-`` instead of ``+`` and ``_`` instead of ``/`` in the 99 standard Base64 alphabet, and return the encoded :class:`bytes`. The result 100 can still contain ``=``. 101 102 103 .. function:: urlsafe_b64decode(s) 104 105 Decode :term:`bytes-like object` or ASCII string *s* 106 using the URL- and filesystem-safe 107 alphabet, which substitutes ``-`` instead of ``+`` and ``_`` instead of 108 ``/`` in the standard Base64 alphabet, and return the decoded 109 :class:`bytes`. 110 111 112 .. function:: b32encode(s) 113 114 Encode the :term:`bytes-like object` *s* using Base32 and return the 115 encoded :class:`bytes`. 116 117 118 .. function:: b32decode(s, casefold=False, map01=None) 119 120 Decode the Base32 encoded :term:`bytes-like object` or ASCII string *s* and 121 return the decoded :class:`bytes`. 122 123 Optional *casefold* is a flag specifying 124 whether a lowercase alphabet is acceptable as input. For security purposes, 125 the default is ``False``. 126 127 :rfc:`3548` allows for optional mapping of the digit 0 (zero) to the letter O 128 (oh), and for optional mapping of the digit 1 (one) to either the letter I (eye) 129 or letter L (el). The optional argument *map01* when not ``None``, specifies 130 which letter the digit 1 should be mapped to (when *map01* is not ``None``, the 131 digit 0 is always mapped to the letter O). For security purposes the default is 132 ``None``, so that 0 and 1 are not allowed in the input. 133 134 A :exc:`binascii.Error` is raised if *s* is 135 incorrectly padded or if there are non-alphabet characters present in the 136 input. 137 138 139 .. function:: b16encode(s) 140 141 Encode the :term:`bytes-like object` *s* using Base16 and return the 142 encoded :class:`bytes`. 143 144 145 .. function:: b16decode(s, casefold=False) 146 147 Decode the Base16 encoded :term:`bytes-like object` or ASCII string *s* and 148 return the decoded :class:`bytes`. 149 150 Optional *casefold* is a flag specifying whether a 151 lowercase alphabet is acceptable as input. For security purposes, the default 152 is ``False``. 153 154 A :exc:`binascii.Error` is raised if *s* is 155 incorrectly padded or if there are non-alphabet characters present in the 156 input. 157 158 159 .. function:: a85encode(b, *, foldspaces=False, wrapcol=0, pad=False, adobe=False) 160 161 Encode the :term:`bytes-like object` *b* using Ascii85 and return the 162 encoded :class:`bytes`. 163 164 *foldspaces* is an optional flag that uses the special short sequence 'y' 165 instead of 4 consecutive spaces (ASCII 0x20) as supported by 'btoa'. This 166 feature is not supported by the "standard" Ascii85 encoding. 167 168 *wrapcol* controls whether the output should have newline (``b'\n'``) 169 characters added to it. If this is non-zero, each output line will be 170 at most this many characters long. 171 172 *pad* controls whether the input is padded to a multiple of 4 173 before encoding. Note that the ``btoa`` implementation always pads. 174 175 *adobe* controls whether the encoded byte sequence is framed with ``<~`` 176 and ``~>``, which is used by the Adobe implementation. 177 178 .. versionadded:: 3.4 179 180 181 .. function:: a85decode(b, *, foldspaces=False, adobe=False, ignorechars=b' \\t\\n\\r\\v') 182 183 Decode the Ascii85 encoded :term:`bytes-like object` or ASCII string *b* and 184 return the decoded :class:`bytes`. 185 186 *foldspaces* is a flag that specifies whether the 'y' short sequence 187 should be accepted as shorthand for 4 consecutive spaces (ASCII 0x20). 188 This feature is not supported by the "standard" Ascii85 encoding. 189 190 *adobe* controls whether the input sequence is in Adobe Ascii85 format 191 (i.e. is framed with <~ and ~>). 192 193 *ignorechars* should be a :term:`bytes-like object` or ASCII string 194 containing characters to ignore 195 from the input. This should only contain whitespace characters, and by 196 default contains all whitespace characters in ASCII. 197 198 .. versionadded:: 3.4 199 200 201 .. function:: b85encode(b, pad=False) 202 203 Encode the :term:`bytes-like object` *b* using base85 (as used in e.g. 204 git-style binary diffs) and return the encoded :class:`bytes`. 205 206 If *pad* is true, the input is padded with ``b'\0'`` so its length is a 207 multiple of 4 bytes before encoding. 208 209 .. versionadded:: 3.4 210 211 212 .. function:: b85decode(b) 213 214 Decode the base85-encoded :term:`bytes-like object` or ASCII string *b* and 215 return the decoded :class:`bytes`. Padding is implicitly removed, if 216 necessary. 217 218 .. versionadded:: 3.4 219 220 221 .. note:: 222 Both Base85 and Ascii85 have an expansion factor of 5 to 4 (5 Base85 or 223 Ascii85 characters can encode 4 binary bytes), while the better-known 224 Base64 has an expansion factor of 6 to 4. They are therefore more 225 efficient when space expensive. They differ by details such as the 226 character map used for encoding. 227 228 229 The legacy interface: 230 231 .. function:: decode(input, output) 232 233 Decode the contents of the binary *input* file and write the resulting binary 234 data to the *output* file. *input* and *output* must be :term:`file objects 235 <file object>`. *input* will be read until ``input.readline()`` returns an 236 empty bytes object. 237 238 239 .. function:: decodebytes(s) 240 241 Decode the :term:`bytes-like object` *s*, which must contain one or more 242 lines of base64 encoded data, and return the decoded :class:`bytes`. 243 244 .. versionadded:: 3.1 245 246 .. function:: decodestring(s) 247 248 Deprecated alias of :func:`decodebytes`. 249 250 .. deprecated:: 3.1 251 252 253 .. function:: encode(input, output) 254 255 Encode the contents of the binary *input* file and write the resulting base64 256 encoded data to the *output* file. *input* and *output* must be :term:`file 257 objects <file object>`. *input* will be read until ``input.read()`` returns 258 an empty bytes object. :func:`encode` inserts a newline character (``b'\n'``) 259 after every 76 bytes of the output, as well as ensuring that the output 260 always ends with a newline, as per :rfc:`2045` (MIME). 261 262 263 .. function:: encodebytes(s) 264 265 Encode the :term:`bytes-like object` *s*, which can contain arbitrary binary 266 data, and return :class:`bytes` containing the base64-encoded data, with newlines 267 (``b'\n'``) inserted after every 76 bytes of output, and ensuring that 268 there is a trailing newline, as per :rfc:`2045` (MIME). 269 270 .. versionadded:: 3.1 271 272 .. function:: encodestring(s) 273 274 Deprecated alias of :func:`encodebytes`. 275 276 .. deprecated:: 3.1 277 278 279 An example usage of the module: 280 281 >>> import base64 282 >>> encoded = base64.b64encode(b'data to be encoded') 283 >>> encoded 284 b'ZGF0YSB0byBiZSBlbmNvZGVk' 285 >>> data = base64.b64decode(encoded) 286 >>> data 287 b'data to be encoded' 288 289 290 .. seealso:: 291 292 Module :mod:`binascii` 293 Support module containing ASCII-to-binary and binary-to-ASCII conversions. 294 295 :rfc:`1521` - MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies 296 Section 5.2, "Base64 Content-Transfer-Encoding," provides the definition of the 297 base64 encoding. 298 299
