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| 54 | |
| 55 | <H1><A NAME="SECTION00141200000000000000000"> |
| 56 | 12.12 <tt class="module">base64</tt> -- |
| 57 | RFC 3548: Base16, Base32, Base64 Data Encodings</A> |
| 58 | </H1> |
| 59 | |
| 60 | <P> |
| 61 | <A NAME="module-base64"></A> |
| 62 | |
| 63 | <P> |
| 64 | <a id='l2h-4108' xml:id='l2h-4108'></a><a id='l2h-4123' xml:id='l2h-4123'></a> |
| 65 | |
| 66 | <P> |
| 67 | This module provides data encoding and decoding as specified in |
| 68 | <a class="rfc" id='rfcref-91230' xml:id='rfcref-91230' |
| 69 | href="http://www.faqs.org/rfcs/rfc3548.html">RFC 3548</a>. This standard defines the Base16, Base32, and Base64 |
| 70 | algorithms for encoding and decoding arbitrary binary strings into |
| 71 | text strings that can be safely sent by email, used as parts of URLs, |
| 72 | or included as part of an HTTP POST request. The encoding algorithm is |
| 73 | not the same as the <b class="program">uuencode</b> program. |
| 74 | |
| 75 | <P> |
| 76 | There are two interfaces provided by this module. The modern |
| 77 | interface supports encoding and decoding string objects using all |
| 78 | three alphabets. The legacy interface provides for encoding and |
| 79 | decoding to and from file-like objects as well as strings, but only |
| 80 | using the Base64 standard alphabet. |
| 81 | |
| 82 | <P> |
| 83 | The modern interface provides: |
| 84 | |
| 85 | <P> |
| 86 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 87 | <td><nobr><b><tt id='l2h-4109' xml:id='l2h-4109' class="function">b64encode</tt></b>(</nobr></td> |
| 88 | <td><var>s</var><big>[</big><var>, altchars</var><big>]</big><var></var>)</td></tr></table></dt> |
| 89 | <dd> |
| 90 | Encode a string use Base64. |
| 91 | |
| 92 | <P> |
| 93 | <var>s</var> is the string to encode. Optional <var>altchars</var> must be a |
| 94 | string of at least length 2 (additional characters are ignored) which |
| 95 | specifies an alternative alphabet for the <code>+</code> and <code>/</code> |
| 96 | characters. This allows an application to e.g. generate URL or |
| 97 | filesystem safe Base64 strings. The default is <code>None</code>, for which |
| 98 | the standard Base64 alphabet is used. |
| 99 | |
| 100 | <P> |
| 101 | The encoded string is returned. |
| 102 | </dl> |
| 103 | |
| 104 | <P> |
| 105 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 106 | <td><nobr><b><tt id='l2h-4110' xml:id='l2h-4110' class="function">b64decode</tt></b>(</nobr></td> |
| 107 | <td><var>s</var><big>[</big><var>, altchars</var><big>]</big><var></var>)</td></tr></table></dt> |
| 108 | <dd> |
| 109 | Decode a Base64 encoded string. |
| 110 | |
| 111 | <P> |
| 112 | <var>s</var> is the string to decode. Optional <var>altchars</var> must be a |
| 113 | string of at least length 2 (additional characters are ignored) which |
| 114 | specifies the alternative alphabet used instead of the <code>+</code> and |
| 115 | <code>/</code> characters. |
| 116 | |
| 117 | <P> |
| 118 | The decoded string is returned. A <tt class="exception">TypeError</tt> is raised if |
| 119 | <var>s</var> were incorrectly padded or if there are non-alphabet |
| 120 | characters present in the string. |
| 121 | </dl> |
| 122 | |
| 123 | <P> |
| 124 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 125 | <td><nobr><b><tt id='l2h-4111' xml:id='l2h-4111' class="function">standard_b64encode</tt></b>(</nobr></td> |
| 126 | <td><var>s</var>)</td></tr></table></dt> |
| 127 | <dd> |
| 128 | Encode string <var>s</var> using the standard Base64 alphabet. |
| 129 | </dl> |
| 130 | |
| 131 | <P> |
| 132 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 133 | <td><nobr><b><tt id='l2h-4112' xml:id='l2h-4112' class="function">standard_b64decode</tt></b>(</nobr></td> |
| 134 | <td><var>s</var>)</td></tr></table></dt> |
| 135 | <dd> |
| 136 | Decode string <var>s</var> using the standard Base64 alphabet. |
| 137 | </dl> |
| 138 | |
| 139 | <P> |
| 140 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 141 | <td><nobr><b><tt id='l2h-4113' xml:id='l2h-4113' class="function">urlsafe_b64encode</tt></b>(</nobr></td> |
| 142 | <td><var>s</var>)</td></tr></table></dt> |
| 143 | <dd> |
| 144 | Encode string <var>s</var> using a URL-safe alphabet, which substitutes |
| 145 | <code>-</code> instead of <code>+</code> and <code>_</code> instead of <code>/</code> in the |
| 146 | standard Base64 alphabet. |
| 147 | </dl> |
| 148 | |
| 149 | <P> |
| 150 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 151 | <td><nobr><b><tt id='l2h-4114' xml:id='l2h-4114' class="function">urlsafe_b64decode</tt></b>(</nobr></td> |
| 152 | <td><var>s</var>)</td></tr></table></dt> |
| 153 | <dd> |
| 154 | Decode string <var>s</var> using a URL-safe alphabet, which substitutes |
| 155 | <code>-</code> instead of <code>+</code> and <code>_</code> instead of <code>/</code> in the |
| 156 | standard Base64 alphabet. |
| 157 | </dl> |
| 158 | |
| 159 | <P> |
| 160 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 161 | <td><nobr><b><tt id='l2h-4115' xml:id='l2h-4115' class="function">b32encode</tt></b>(</nobr></td> |
| 162 | <td><var>s</var>)</td></tr></table></dt> |
| 163 | <dd> |
| 164 | Encode a string using Base32. <var>s</var> is the string to encode. The |
| 165 | encoded string is returned. |
| 166 | </dl> |
| 167 | |
| 168 | <P> |
| 169 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 170 | <td><nobr><b><tt id='l2h-4116' xml:id='l2h-4116' class="function">b32decode</tt></b>(</nobr></td> |
| 171 | <td><var>s</var><big>[</big><var>, casefold</var><big>[</big><var>, map01</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> |
| 172 | <dd> |
| 173 | Decode a Base32 encoded string. |
| 174 | |
| 175 | <P> |
| 176 | <var>s</var> is the string to decode. Optional <var>casefold</var> is a flag |
| 177 | specifying whether a lowercase alphabet is acceptable as input. For |
| 178 | security purposes, the default is <code>False</code>. |
| 179 | |
| 180 | <P> |
| 181 | <a class="rfc" id='rfcref-91232' xml:id='rfcref-91232' |
| 182 | href="http://www.faqs.org/rfcs/rfc3548.html">RFC 3548</a> allows for optional mapping of the digit 0 (zero) to the |
| 183 | letter O (oh), and for optional mapping of the digit 1 (one) to either |
| 184 | the letter I (eye) or letter L (el). The optional argument |
| 185 | <var>map01</var> when not <code>None</code>, specifies which letter the digit 1 should |
| 186 | be mapped to (when map01 is not <var>None</var>, the digit 0 is always |
| 187 | mapped to the letter O). For security purposes the default is |
| 188 | <code>None</code>, so that 0 and 1 are not allowed in the input. |
| 189 | |
| 190 | <P> |
| 191 | The decoded string is returned. A <tt class="exception">TypeError</tt> is raised if |
| 192 | <var>s</var> were incorrectly padded or if there are non-alphabet characters |
| 193 | present in the string. |
| 194 | </dl> |
| 195 | |
| 196 | <P> |
| 197 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 198 | <td><nobr><b><tt id='l2h-4117' xml:id='l2h-4117' class="function">b16encode</tt></b>(</nobr></td> |
| 199 | <td><var>s</var>)</td></tr></table></dt> |
| 200 | <dd> |
| 201 | Encode a string using Base16. |
| 202 | |
| 203 | <P> |
| 204 | <var>s</var> is the string to encode. The encoded string is returned. |
| 205 | </dl> |
| 206 | |
| 207 | <P> |
| 208 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 209 | <td><nobr><b><tt id='l2h-4118' xml:id='l2h-4118' class="function">b16decode</tt></b>(</nobr></td> |
| 210 | <td><var>s</var><big>[</big><var>, casefold</var><big>]</big><var></var>)</td></tr></table></dt> |
| 211 | <dd> |
| 212 | Decode a Base16 encoded string. |
| 213 | |
| 214 | <P> |
| 215 | <var>s</var> is the string to decode. Optional <var>casefold</var> is a flag |
| 216 | specifying whether a lowercase alphabet is acceptable as input. For |
| 217 | security purposes, the default is <code>False</code>. |
| 218 | |
| 219 | <P> |
| 220 | The decoded string is returned. A <tt class="exception">TypeError</tt> is raised if |
| 221 | <var>s</var> were incorrectly padded or if there are non-alphabet |
| 222 | characters present in the string. |
| 223 | </dl> |
| 224 | |
| 225 | <P> |
| 226 | The legacy interface: |
| 227 | |
| 228 | <P> |
| 229 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 230 | <td><nobr><b><tt id='l2h-4119' xml:id='l2h-4119' class="function">decode</tt></b>(</nobr></td> |
| 231 | <td><var>input, output</var>)</td></tr></table></dt> |
| 232 | <dd> |
| 233 | Decode the contents of the <var>input</var> file and write the resulting |
| 234 | binary data to the <var>output</var> file. |
| 235 | <var>input</var> and <var>output</var> must either be file objects or objects that |
| 236 | mimic the file object interface. <var>input</var> will be read until |
| 237 | <code><var>input</var>.read()</code> returns an empty string. |
| 238 | </dl> |
| 239 | |
| 240 | <P> |
| 241 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 242 | <td><nobr><b><tt id='l2h-4120' xml:id='l2h-4120' class="function">decodestring</tt></b>(</nobr></td> |
| 243 | <td><var>s</var>)</td></tr></table></dt> |
| 244 | <dd> |
| 245 | Decode the string <var>s</var>, which must contain one or more lines of |
| 246 | base64 encoded data, and return a string containing the resulting |
| 247 | binary data. |
| 248 | </dl> |
| 249 | |
| 250 | <P> |
| 251 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 252 | <td><nobr><b><tt id='l2h-4121' xml:id='l2h-4121' class="function">encode</tt></b>(</nobr></td> |
| 253 | <td><var>input, output</var>)</td></tr></table></dt> |
| 254 | <dd> |
| 255 | Encode the contents of the <var>input</var> file and write the resulting |
| 256 | base64 encoded data to the <var>output</var> file. |
| 257 | <var>input</var> and <var>output</var> must either be file objects or objects that |
| 258 | mimic the file object interface. <var>input</var> will be read until |
| 259 | <code><var>input</var>.read()</code> returns an empty string. <tt class="function">encode()</tt> |
| 260 | returns the encoded data plus a trailing newline character |
| 261 | (<code>'\n'</code>). |
| 262 | </dl> |
| 263 | |
| 264 | <P> |
| 265 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 266 | <td><nobr><b><tt id='l2h-4122' xml:id='l2h-4122' class="function">encodestring</tt></b>(</nobr></td> |
| 267 | <td><var>s</var>)</td></tr></table></dt> |
| 268 | <dd> |
| 269 | Encode the string <var>s</var>, which can contain arbitrary binary data, |
| 270 | and return a string containing one or more lines of |
| 271 | base64-encoded data. <tt class="function">encodestring()</tt> returns a |
| 272 | string containing one or more lines of base64-encoded data |
| 273 | always including an extra trailing newline (<code>'\n'</code>). |
| 274 | </dl> |
| 275 | |
| 276 | <P> |
| 277 | <div class="seealso"> |
| 278 | <p class="heading">See Also:</p> |
| 279 | |
| 280 | <dl compact="compact" class="seemodule"> |
| 281 | <dt>Module <b><tt class="module"><a href="module-binascii.html">binascii</a></tt>:</b> |
| 282 | <dd>Support module containing ASCII-to-binary |
| 283 | and binary-to-ASCII conversions. |
| 284 | </dl> |
| 285 | <dl compact="compact" class="seerfc"> |
| 286 | <dt><a href="http://www.faqs.org/rfcs/rfc1521.html" |
| 287 | title="MIME (Multipurpose Internet Mail Extensions) Part One: |
| 288 | Mechanisms for Specifying and Describing the Format of |
| 289 | Internet Message Bodies" |
| 290 | >RFC 1521, <em>MIME (Multipurpose Internet Mail Extensions) Part One: |
| 291 | Mechanisms for Specifying and Describing the Format of |
| 292 | Internet Message Bodies</em></a> |
| 293 | <dd>Section 5.2, ``Base64 |
| 294 | Content-Transfer-Encoding,'' provides the definition of the |
| 295 | base64 encoding. |
| 296 | </dl> |
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