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<H1><A NAME="SECTION00141200000000000000000">
12.12 <tt class="module">base64</tt> --
	 RFC 3548: Base16, Base32, Base64 Data Encodings</A>
</H1>

<P>
<A NAME="module-base64"></A>

<P>
<a id='l2h-4108' xml:id='l2h-4108'></a><a id='l2h-4123' xml:id='l2h-4123'></a>

<P>
This module provides data encoding and decoding as specified in
<a class="rfc" id='rfcref-91230' xml:id='rfcref-91230'
href="http://www.faqs.org/rfcs/rfc3548.html">RFC 3548</a>.  This standard defines the Base16, Base32, and Base64
algorithms for encoding and decoding arbitrary binary strings into
text strings that can be safely sent by email, used as parts of URLs,
or included as part of an HTTP POST request.  The encoding algorithm is
not the same as the <b class="program">uuencode</b> program.

<P>
There are two interfaces provided by this module.  The modern
interface supports encoding and decoding string objects using all
three alphabets.  The legacy interface provides for encoding and
decoding to and from file-like objects as well as strings, but only
using the Base64 standard alphabet.

<P>
The modern interface provides:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4109' xml:id='l2h-4109' class="function">b64encode</tt></b>(</nobr></td>
  <td><var>s</var><big>[</big><var>, altchars</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Encode a string use Base64.

<P>
<var>s</var> is the string to encode.  Optional <var>altchars</var> must be a
string of at least length 2 (additional characters are ignored) which
specifies an alternative alphabet for the <code>+</code> and <code>/</code>
characters.  This allows an application to e.g. generate URL or
filesystem safe Base64 strings.  The default is <code>None</code>, for which
the standard Base64 alphabet is used.

<P>
The encoded string is returned.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4110' xml:id='l2h-4110' class="function">b64decode</tt></b>(</nobr></td>
  <td><var>s</var><big>[</big><var>, altchars</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Decode a Base64 encoded string.

<P>
<var>s</var> is the string to decode.  Optional <var>altchars</var> must be a
string of at least length 2 (additional characters are ignored) which
specifies the alternative alphabet used instead of the <code>+</code> and
<code>/</code> characters.

<P>
The decoded string is returned.  A <tt class="exception">TypeError</tt> is raised if
<var>s</var> were incorrectly padded or if there are non-alphabet
characters present in the string.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4111' xml:id='l2h-4111' class="function">standard_b64encode</tt></b>(</nobr></td>
  <td><var>s</var>)</td></tr></table></dt>
<dd>
Encode string <var>s</var> using the standard Base64 alphabet.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4112' xml:id='l2h-4112' class="function">standard_b64decode</tt></b>(</nobr></td>
  <td><var>s</var>)</td></tr></table></dt>
<dd>
Decode string <var>s</var> using the standard Base64 alphabet.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4113' xml:id='l2h-4113' class="function">urlsafe_b64encode</tt></b>(</nobr></td>
  <td><var>s</var>)</td></tr></table></dt>
<dd>
Encode string <var>s</var> using a URL-safe alphabet, which substitutes
<code>-</code> instead of <code>+</code> and <code>_</code> instead of <code>/</code> in the
standard Base64 alphabet.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4114' xml:id='l2h-4114' class="function">urlsafe_b64decode</tt></b>(</nobr></td>
  <td><var>s</var>)</td></tr></table></dt>
<dd>
Decode string <var>s</var> using a URL-safe alphabet, which substitutes
<code>-</code> instead of <code>+</code> and <code>_</code> instead of <code>/</code> in the
standard Base64 alphabet.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4115' xml:id='l2h-4115' class="function">b32encode</tt></b>(</nobr></td>
  <td><var>s</var>)</td></tr></table></dt>
<dd>
Encode a string using Base32.  <var>s</var> is the string to encode.  The
encoded string is returned.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4116' xml:id='l2h-4116' class="function">b32decode</tt></b>(</nobr></td>
  <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>
<dd>
Decode a Base32 encoded string.

<P>
<var>s</var> is the string to decode.  Optional <var>casefold</var> is a flag
specifying whether a lowercase alphabet is acceptable as input.  For
security purposes, the default is <code>False</code>.

<P>
<a class="rfc" id='rfcref-91232' xml:id='rfcref-91232'
href="http://www.faqs.org/rfcs/rfc3548.html">RFC 3548</a> allows for optional mapping of the digit 0 (zero) to the
letter O (oh), and for optional mapping of the digit 1 (one) to either
the letter I (eye) or letter L (el).  The optional argument
<var>map01</var> when not <code>None</code>, specifies which letter the digit 1 should
be mapped to (when map01 is not <var>None</var>, the digit 0 is always
mapped to the letter O).  For security purposes the default is
<code>None</code>, so that 0 and 1 are not allowed in the input.

<P>
The decoded string is returned.  A <tt class="exception">TypeError</tt> is raised if
<var>s</var> were incorrectly padded or if there are non-alphabet characters
present in the string.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4117' xml:id='l2h-4117' class="function">b16encode</tt></b>(</nobr></td>
  <td><var>s</var>)</td></tr></table></dt>
<dd>
Encode a string using Base16.

<P>
<var>s</var> is the string to encode.  The encoded string is returned.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4118' xml:id='l2h-4118' class="function">b16decode</tt></b>(</nobr></td>
  <td><var>s</var><big>[</big><var>, casefold</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Decode a Base16 encoded string.

<P>
<var>s</var> is the string to decode.  Optional <var>casefold</var> is a flag
specifying whether a lowercase alphabet is acceptable as input.  For
security purposes, the default is <code>False</code>.

<P>
The decoded string is returned.  A <tt class="exception">TypeError</tt> is raised if
<var>s</var> were incorrectly padded or if there are non-alphabet
characters present in the string.
</dl>

<P>
The legacy interface:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4119' xml:id='l2h-4119' class="function">decode</tt></b>(</nobr></td>
  <td><var>input, output</var>)</td></tr></table></dt>
<dd>
Decode the contents of the <var>input</var> file and write the resulting
binary data to the <var>output</var> file.
<var>input</var> and <var>output</var> must either be file objects or objects that
mimic the file object interface. <var>input</var> will be read until
<code><var>input</var>.read()</code> returns an empty string.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4120' xml:id='l2h-4120' class="function">decodestring</tt></b>(</nobr></td>
  <td><var>s</var>)</td></tr></table></dt>
<dd>
Decode the string <var>s</var>, which must contain one or more lines of
base64 encoded data, and return a string containing the resulting
binary data.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4121' xml:id='l2h-4121' class="function">encode</tt></b>(</nobr></td>
  <td><var>input, output</var>)</td></tr></table></dt>
<dd>
Encode the contents of the <var>input</var> file and write the resulting
base64 encoded data to the <var>output</var> file.
<var>input</var> and <var>output</var> must either be file objects or objects that
mimic the file object interface. <var>input</var> will be read until
<code><var>input</var>.read()</code> returns an empty string.  <tt class="function">encode()</tt>
returns the encoded data plus a trailing newline character
(<code>'&#92;n'</code>).
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4122' xml:id='l2h-4122' class="function">encodestring</tt></b>(</nobr></td>
  <td><var>s</var>)</td></tr></table></dt>
<dd>
Encode the string <var>s</var>, which can contain arbitrary binary data,
and return a string containing one or more lines of
base64-encoded data.  <tt class="function">encodestring()</tt> returns a
string containing one or more lines of base64-encoded data
always including an extra trailing newline (<code>'&#92;n'</code>).
</dl>

<P>
<div class="seealso">
  <p class="heading">See Also:</p>

  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-binascii.html">binascii</a></tt>:</b>
    <dd>Support module containing ASCII-to-binary
                       and binary-to-ASCII conversions.
  </dl>
  <dl compact="compact" class="seerfc">
    <dt><a href="http://www.faqs.org/rfcs/rfc1521.html"
        title="MIME (Multipurpose Internet Mail Extensions) Part One:
          Mechanisms for Specifying and Describing the Format of
          Internet Message Bodies"
        >RFC 1521, <em>MIME (Multipurpose Internet Mail Extensions) Part One:
          Mechanisms for Specifying and Describing the Format of
          Internet Message Bodies</em></a>
    <dd>Section 5.2, ``Base64
          Content-Transfer-Encoding,'' provides the definition of the
          base64 encoding.
  </dl>
</div>

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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>
297	</div>
298
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