AppPkg/Applications/Python/Python-2.7.2/Lib/email/message.py

   1 # Copyright (C) 2001-2006 Python Software Foundation
   2 # Author: Barry Warsaw
   3 # Contact: email-sig@python.org
   4
   5 """Basic message object for the email package object model."""
   6
   7 __all__ = ['Message']
   8
   9 import re
  10 import uu
  11 import binascii
  12 import warnings
  13 from cStringIO import StringIO
  14
  15 # Intrapackage imports
  16 import email.charset
  17 from email import utils
  18 from email import errors
  19
  20 SEMISPACE = '; '
  21
  22 # Regular expression that matches `special' characters in parameters, the
  23 # existence of which force quoting of the parameter value.
  24 tspecials = re.compile(r'[ \(\)<>@,;:\\"/\[\]\?=]')
  25
  26
  27 # Helper functions
  28 def _splitparam(param):
  29     # Split header parameters.  BAW: this may be too simple.  It isn't
  30     # strictly RFC 2045 (section 5.1) compliant, but it catches most headers
  31     # found in the wild.  We may eventually need a full fledged parser
  32     # eventually.
  33     a, sep, b = param.partition(';')
  34     if not sep:
  35         return a.strip(), None
  36     return a.strip(), b.strip()
  37 \f
  38 def _formatparam(param, value=None, quote=True):
  39     """Convenience function to format and return a key=value pair.
  40
  41     This will quote the value if needed or if quote is true.  If value is a
  42     three tuple (charset, language, value), it will be encoded according
  43     to RFC2231 rules.
  44     """
  45     if value is not None and len(value) > 0:
  46         # A tuple is used for RFC 2231 encoded parameter values where items
  47         # are (charset, language, value).  charset is a string, not a Charset
  48         # instance.
  49         if isinstance(value, tuple):
  50             # Encode as per RFC 2231
  51             param += '*'
  52             value = utils.encode_rfc2231(value[2], value[0], value[1])
  53         # BAW: Please check this.  I think that if quote is set it should
  54         # force quoting even if not necessary.
  55         if quote or tspecials.search(value):
  56             return '%s="%s"' % (param, utils.quote(value))
  57         else:
  58             return '%s=%s' % (param, value)
  59     else:
  60         return param
  61
  62 def _parseparam(s):
  63     plist = []
  64     while s[:1] == ';':
  65         s = s[1:]
  66         end = s.find(';')
  67         while end > 0 and (s.count('"', 0, end) - s.count('\\"', 0, end)) % 2:
  68             end = s.find(';', end + 1)
  69         if end < 0:
  70             end = len(s)
  71         f = s[:end]
  72         if '=' in f:
  73             i = f.index('=')
  74             f = f[:i].strip().lower() + '=' + f[i+1:].strip()
  75         plist.append(f.strip())
  76         s = s[end:]
  77     return plist
  78
  79
  80 def _unquotevalue(value):
  81     # This is different than utils.collapse_rfc2231_value() because it doesn't
  82     # try to convert the value to a unicode.  Message.get_param() and
  83     # Message.get_params() are both currently defined to return the tuple in
  84     # the face of RFC 2231 parameters.
  85     if isinstance(value, tuple):
  86         return value[0], value[1], utils.unquote(value[2])
  87     else:
  88         return utils.unquote(value)
  89
  90
  91 \f
  92 class Message:
  93     """Basic message object.
  94
  95     A message object is defined as something that has a bunch of RFC 2822
  96     headers and a payload.  It may optionally have an envelope header
  97     (a.k.a. Unix-From or From_ header).  If the message is a container (i.e. a
  98     multipart or a message/rfc822), then the payload is a list of Message
  99     objects, otherwise it is a string.
 100
 101     Message objects implement part of the `mapping' interface, which assumes
 102     there is exactly one occurrence of the header per message.  Some headers
 103     do in fact appear multiple times (e.g. Received) and for those headers,
 104     you must use the explicit API to set or get all the headers.  Not all of
 105     the mapping methods are implemented.
 106     """
 107     def __init__(self):
 108         self._headers = []
 109         self._unixfrom = None
 110         self._payload = None
 111         self._charset = None
 112         # Defaults for multipart messages
 113         self.preamble = self.epilogue = None
 114         self.defects = []
 115         # Default content type
 116         self._default_type = 'text/plain'
 117
 118     def __str__(self):
 119         """Return the entire formatted message as a string.
 120         This includes the headers, body, and envelope header.
 121         """
 122         return self.as_string(unixfrom=True)
 123
 124     def as_string(self, unixfrom=False):
 125         """Return the entire formatted message as a string.
 126         Optional `unixfrom' when True, means include the Unix From_ envelope
 127         header.
 128
 129         This is a convenience method and may not generate the message exactly
 130         as you intend because by default it mangles lines that begin with
 131         "From ".  For more flexibility, use the flatten() method of a
 132         Generator instance.
 133         """
 134         from email.generator import Generator
 135         fp = StringIO()
 136         g = Generator(fp)
 137         g.flatten(self, unixfrom=unixfrom)
 138         return fp.getvalue()
 139
 140     def is_multipart(self):
 141         """Return True if the message consists of multiple parts."""
 142         return isinstance(self._payload, list)
 143
 144     #
 145     # Unix From_ line
 146     #
 147     def set_unixfrom(self, unixfrom):
 148         self._unixfrom = unixfrom
 149
 150     def get_unixfrom(self):
 151         return self._unixfrom
 152
 153     #
 154     # Payload manipulation.
 155     #
 156     def attach(self, payload):
 157         """Add the given payload to the current payload.
 158
 159         The current payload will always be a list of objects after this method
 160         is called.  If you want to set the payload to a scalar object, use
 161         set_payload() instead.
 162         """
 163         if self._payload is None:
 164             self._payload = [payload]
 165         else:
 166             self._payload.append(payload)
 167
 168     def get_payload(self, i=None, decode=False):
 169         """Return a reference to the payload.
 170
 171         The payload will either be a list object or a string.  If you mutate
 172         the list object, you modify the message's payload in place.  Optional
 173         i returns that index into the payload.
 174
 175         Optional decode is a flag indicating whether the payload should be
 176         decoded or not, according to the Content-Transfer-Encoding header
 177         (default is False).
 178
 179         When True and the message is not a multipart, the payload will be
 180         decoded if this header's value is `quoted-printable' or `base64'.  If
 181         some other encoding is used, or the header is missing, or if the
 182         payload has bogus data (i.e. bogus base64 or uuencoded data), the
 183         payload is returned as-is.
 184
 185         If the message is a multipart and the decode flag is True, then None
 186         is returned.
 187         """
 188         if i is None:
 189             payload = self._payload
 190         elif not isinstance(self._payload, list):
 191             raise TypeError('Expected list, got %s' % type(self._payload))
 192         else:
 193             payload = self._payload[i]
 194         if decode:
 195             if self.is_multipart():
 196                 return None
 197             cte = self.get('content-transfer-encoding', '').lower()
 198             if cte == 'quoted-printable':
 199                 return utils._qdecode(payload)
 200             elif cte == 'base64':
 201                 try:
 202                     return utils._bdecode(payload)
 203                 except binascii.Error:
 204                     # Incorrect padding
 205                     return payload
 206             elif cte in ('x-uuencode', 'uuencode', 'uue', 'x-uue'):
 207                 sfp = StringIO()
 208                 try:
 209                     uu.decode(StringIO(payload+'\n'), sfp, quiet=True)
 210                     payload = sfp.getvalue()
 211                 except uu.Error:
 212                     # Some decoding problem
 213                     return payload
 214         # Everything else, including encodings with 8bit or 7bit are returned
 215         # unchanged.
 216         return payload
 217
 218     def set_payload(self, payload, charset=None):
 219         """Set the payload to the given value.
 220
 221         Optional charset sets the message's default character set.  See
 222         set_charset() for details.
 223         """
 224         self._payload = payload
 225         if charset is not None:
 226             self.set_charset(charset)
 227
 228     def set_charset(self, charset):
 229         """Set the charset of the payload to a given character set.
 230
 231         charset can be a Charset instance, a string naming a character set, or
 232         None.  If it is a string it will be converted to a Charset instance.
 233         If charset is None, the charset parameter will be removed from the
 234         Content-Type field.  Anything else will generate a TypeError.
 235
 236         The message will be assumed to be of type text/* encoded with
 237         charset.input_charset.  It will be converted to charset.output_charset
 238         and encoded properly, if needed, when generating the plain text
 239         representation of the message.  MIME headers (MIME-Version,
 240         Content-Type, Content-Transfer-Encoding) will be added as needed.
 241
 242         """
 243         if charset is None:
 244             self.del_param('charset')
 245             self._charset = None
 246             return
 247         if isinstance(charset, basestring):
 248             charset = email.charset.Charset(charset)
 249         if not isinstance(charset, email.charset.Charset):
 250             raise TypeError(charset)
 251         # BAW: should we accept strings that can serve as arguments to the
 252         # Charset constructor?
 253         self._charset = charset
 254         if 'MIME-Version' not in self:
 255             self.add_header('MIME-Version', '1.0')
 256         if 'Content-Type' not in self:
 257             self.add_header('Content-Type', 'text/plain',
 258                             charset=charset.get_output_charset())
 259         else:
 260             self.set_param('charset', charset.get_output_charset())
 261         if isinstance(self._payload, unicode):
 262             self._payload = self._payload.encode(charset.output_charset)
 263         if str(charset) != charset.get_output_charset():
 264             self._payload = charset.body_encode(self._payload)
 265         if 'Content-Transfer-Encoding' not in self:
 266             cte = charset.get_body_encoding()
 267             try:
 268                 cte(self)
 269             except TypeError:
 270                 self._payload = charset.body_encode(self._payload)
 271                 self.add_header('Content-Transfer-Encoding', cte)
 272
 273     def get_charset(self):
 274         """Return the Charset instance associated with the message's payload.
 275         """
 276         return self._charset
 277
 278     #
 279     # MAPPING INTERFACE (partial)
 280     #
 281     def __len__(self):
 282         """Return the total number of headers, including duplicates."""
 283         return len(self._headers)
 284
 285     def __getitem__(self, name):
 286         """Get a header value.
 287
 288         Return None if the header is missing instead of raising an exception.
 289
 290         Note that if the header appeared multiple times, exactly which
 291         occurrence gets returned is undefined.  Use get_all() to get all
 292         the values matching a header field name.
 293         """
 294         return self.get(name)
 295
 296     def __setitem__(self, name, val):
 297         """Set the value of a header.
 298
 299         Note: this does not overwrite an existing header with the same field
 300         name.  Use __delitem__() first to delete any existing headers.
 301         """
 302         self._headers.append((name, val))
 303
 304     def __delitem__(self, name):
 305         """Delete all occurrences of a header, if present.
 306
 307         Does not raise an exception if the header is missing.
 308         """
 309         name = name.lower()
 310         newheaders = []
 311         for k, v in self._headers:
 312             if k.lower() != name:
 313                 newheaders.append((k, v))
 314         self._headers = newheaders
 315
 316     def __contains__(self, name):
 317         return name.lower() in [k.lower() for k, v in self._headers]
 318
 319     def has_key(self, name):
 320         """Return true if the message contains the header."""
 321         missing = object()
 322         return self.get(name, missing) is not missing
 323
 324     def keys(self):
 325         """Return a list of all the message's header field names.
 326
 327         These will be sorted in the order they appeared in the original
 328         message, or were added to the message, and may contain duplicates.
 329         Any fields deleted and re-inserted are always appended to the header
 330         list.
 331         """
 332         return [k for k, v in self._headers]
 333
 334     def values(self):
 335         """Return a list of all the message's header values.
 336
 337         These will be sorted in the order they appeared in the original
 338         message, or were added to the message, and may contain duplicates.
 339         Any fields deleted and re-inserted are always appended to the header
 340         list.
 341         """
 342         return [v for k, v in self._headers]
 343
 344     def items(self):
 345         """Get all the message's header fields and values.
 346
 347         These will be sorted in the order they appeared in the original
 348         message, or were added to the message, and may contain duplicates.
 349         Any fields deleted and re-inserted are always appended to the header
 350         list.
 351         """
 352         return self._headers[:]
 353
 354     def get(self, name, failobj=None):
 355         """Get a header value.
 356
 357         Like __getitem__() but return failobj instead of None when the field
 358         is missing.
 359         """
 360         name = name.lower()
 361         for k, v in self._headers:
 362             if k.lower() == name:
 363                 return v
 364         return failobj
 365
 366     #
 367     # Additional useful stuff
 368     #
 369
 370     def get_all(self, name, failobj=None):
 371         """Return a list of all the values for the named field.
 372
 373         These will be sorted in the order they appeared in the original
 374         message, and may contain duplicates.  Any fields deleted and
 375         re-inserted are always appended to the header list.
 376
 377         If no such fields exist, failobj is returned (defaults to None).
 378         """
 379         values = []
 380         name = name.lower()
 381         for k, v in self._headers:
 382             if k.lower() == name:
 383                 values.append(v)
 384         if not values:
 385             return failobj
 386         return values
 387
 388     def add_header(self, _name, _value, **_params):
 389         """Extended header setting.
 390
 391         name is the header field to add.  keyword arguments can be used to set
 392         additional parameters for the header field, with underscores converted
 393         to dashes.  Normally the parameter will be added as key="value" unless
 394         value is None, in which case only the key will be added.  If a
 395         parameter value contains non-ASCII characters it must be specified as a
 396         three-tuple of (charset, language, value), in which case it will be
 397         encoded according to RFC2231 rules.
 398
 399         Example:
 400
 401         msg.add_header('content-disposition', 'attachment', filename='bud.gif')
 402         """
 403         parts = []
 404         for k, v in _params.items():
 405             if v is None:
 406                 parts.append(k.replace('_', '-'))
 407             else:
 408                 parts.append(_formatparam(k.replace('_', '-'), v))
 409         if _value is not None:
 410             parts.insert(0, _value)
 411         self._headers.append((_name, SEMISPACE.join(parts)))
 412
 413     def replace_header(self, _name, _value):
 414         """Replace a header.
 415
 416         Replace the first matching header found in the message, retaining
 417         header order and case.  If no matching header was found, a KeyError is
 418         raised.
 419         """
 420         _name = _name.lower()
 421         for i, (k, v) in zip(range(len(self._headers)), self._headers):
 422             if k.lower() == _name:
 423                 self._headers[i] = (k, _value)
 424                 break
 425         else:
 426             raise KeyError(_name)
 427
 428     #
 429     # Use these three methods instead of the three above.
 430     #
 431
 432     def get_content_type(self):
 433         """Return the message's content type.
 434
 435         The returned string is coerced to lower case of the form
 436         `maintype/subtype'.  If there was no Content-Type header in the
 437         message, the default type as given by get_default_type() will be
 438         returned.  Since according to RFC 2045, messages always have a default
 439         type this will always return a value.
 440
 441         RFC 2045 defines a message's default type to be text/plain unless it
 442         appears inside a multipart/digest container, in which case it would be
 443         message/rfc822.
 444         """
 445         missing = object()
 446         value = self.get('content-type', missing)
 447         if value is missing:
 448             # This should have no parameters
 449             return self.get_default_type()
 450         ctype = _splitparam(value)[0].lower()
 451         # RFC 2045, section 5.2 says if its invalid, use text/plain
 452         if ctype.count('/') != 1:
 453             return 'text/plain'
 454         return ctype
 455
 456     def get_content_maintype(self):
 457         """Return the message's main content type.
 458
 459         This is the `maintype' part of the string returned by
 460         get_content_type().
 461         """
 462         ctype = self.get_content_type()
 463         return ctype.split('/')[0]
 464
 465     def get_content_subtype(self):
 466         """Returns the message's sub-content type.
 467
 468         This is the `subtype' part of the string returned by
 469         get_content_type().
 470         """
 471         ctype = self.get_content_type()
 472         return ctype.split('/')[1]
 473
 474     def get_default_type(self):
 475         """Return the `default' content type.
 476
 477         Most messages have a default content type of text/plain, except for
 478         messages that are subparts of multipart/digest containers.  Such
 479         subparts have a default content type of message/rfc822.
 480         """
 481         return self._default_type
 482
 483     def set_default_type(self, ctype):
 484         """Set the `default' content type.
 485
 486         ctype should be either "text/plain" or "message/rfc822", although this
 487         is not enforced.  The default content type is not stored in the
 488         Content-Type header.
 489         """
 490         self._default_type = ctype
 491
 492     def _get_params_preserve(self, failobj, header):
 493         # Like get_params() but preserves the quoting of values.  BAW:
 494         # should this be part of the public interface?
 495         missing = object()
 496         value = self.get(header, missing)
 497         if value is missing:
 498             return failobj
 499         params = []
 500         for p in _parseparam(';' + value):
 501             try:
 502                 name, val = p.split('=', 1)
 503                 name = name.strip()
 504                 val = val.strip()
 505             except ValueError:
 506                 # Must have been a bare attribute
 507                 name = p.strip()
 508                 val = ''
 509             params.append((name, val))
 510         params = utils.decode_params(params)
 511         return params
 512
 513     def get_params(self, failobj=None, header='content-type', unquote=True):
 514         """Return the message's Content-Type parameters, as a list.
 515
 516         The elements of the returned list are 2-tuples of key/value pairs, as
 517         split on the `=' sign.  The left hand side of the `=' is the key,
 518         while the right hand side is the value.  If there is no `=' sign in
 519         the parameter the value is the empty string.  The value is as
 520         described in the get_param() method.
 521
 522         Optional failobj is the object to return if there is no Content-Type
 523         header.  Optional header is the header to search instead of
 524         Content-Type.  If unquote is True, the value is unquoted.
 525         """
 526         missing = object()
 527         params = self._get_params_preserve(missing, header)
 528         if params is missing:
 529             return failobj
 530         if unquote:
 531             return [(k, _unquotevalue(v)) for k, v in params]
 532         else:
 533             return params
 534
 535     def get_param(self, param, failobj=None, header='content-type',
 536                   unquote=True):
 537         """Return the parameter value if found in the Content-Type header.
 538
 539         Optional failobj is the object to return if there is no Content-Type
 540         header, or the Content-Type header has no such parameter.  Optional
 541         header is the header to search instead of Content-Type.
 542
 543         Parameter keys are always compared case insensitively.  The return
 544         value can either be a string, or a 3-tuple if the parameter was RFC
 545         2231 encoded.  When it's a 3-tuple, the elements of the value are of
 546         the form (CHARSET, LANGUAGE, VALUE).  Note that both CHARSET and
 547         LANGUAGE can be None, in which case you should consider VALUE to be
 548         encoded in the us-ascii charset.  You can usually ignore LANGUAGE.
 549
 550         Your application should be prepared to deal with 3-tuple return
 551         values, and can convert the parameter to a Unicode string like so:
 552
 553             param = msg.get_param('foo')
 554             if isinstance(param, tuple):
 555                 param = unicode(param[2], param[0] or 'us-ascii')
 556
 557         In any case, the parameter value (either the returned string, or the
 558         VALUE item in the 3-tuple) is always unquoted, unless unquote is set
 559         to False.
 560         """
 561         if header not in self:
 562             return failobj
 563         for k, v in self._get_params_preserve(failobj, header):
 564             if k.lower() == param.lower():
 565                 if unquote:
 566                     return _unquotevalue(v)
 567                 else:
 568                     return v
 569         return failobj
 570
 571     def set_param(self, param, value, header='Content-Type', requote=True,
 572                   charset=None, language=''):
 573         """Set a parameter in the Content-Type header.
 574
 575         If the parameter already exists in the header, its value will be
 576         replaced with the new value.
 577
 578         If header is Content-Type and has not yet been defined for this
 579         message, it will be set to "text/plain" and the new parameter and
 580         value will be appended as per RFC 2045.
 581
 582         An alternate header can specified in the header argument, and all
 583         parameters will be quoted as necessary unless requote is False.
 584
 585         If charset is specified, the parameter will be encoded according to RFC
 586         2231.  Optional language specifies the RFC 2231 language, defaulting
 587         to the empty string.  Both charset and language should be strings.
 588         """
 589         if not isinstance(value, tuple) and charset:
 590             value = (charset, language, value)
 591
 592         if header not in self and header.lower() == 'content-type':
 593             ctype = 'text/plain'
 594         else:
 595             ctype = self.get(header)
 596         if not self.get_param(param, header=header):
 597             if not ctype:
 598                 ctype = _formatparam(param, value, requote)
 599             else:
 600                 ctype = SEMISPACE.join(
 601                     [ctype, _formatparam(param, value, requote)])
 602         else:
 603             ctype = ''
 604             for old_param, old_value in self.get_params(header=header,
 605                                                         unquote=requote):
 606                 append_param = ''
 607                 if old_param.lower() == param.lower():
 608                     append_param = _formatparam(param, value, requote)
 609                 else:
 610                     append_param = _formatparam(old_param, old_value, requote)
 611                 if not ctype:
 612                     ctype = append_param
 613                 else:
 614                     ctype = SEMISPACE.join([ctype, append_param])
 615         if ctype != self.get(header):
 616             del self[header]
 617             self[header] = ctype
 618
 619     def del_param(self, param, header='content-type', requote=True):
 620         """Remove the given parameter completely from the Content-Type header.
 621
 622         The header will be re-written in place without the parameter or its
 623         value. All values will be quoted as necessary unless requote is
 624         False.  Optional header specifies an alternative to the Content-Type
 625         header.
 626         """
 627         if header not in self:
 628             return
 629         new_ctype = ''
 630         for p, v in self.get_params(header=header, unquote=requote):
 631             if p.lower() != param.lower():
 632                 if not new_ctype:
 633                     new_ctype = _formatparam(p, v, requote)
 634                 else:
 635                     new_ctype = SEMISPACE.join([new_ctype,
 636                                                 _formatparam(p, v, requote)])
 637         if new_ctype != self.get(header):
 638             del self[header]
 639             self[header] = new_ctype
 640
 641     def set_type(self, type, header='Content-Type', requote=True):
 642         """Set the main type and subtype for the Content-Type header.
 643
 644         type must be a string in the form "maintype/subtype", otherwise a
 645         ValueError is raised.
 646
 647         This method replaces the Content-Type header, keeping all the
 648         parameters in place.  If requote is False, this leaves the existing
 649         header's quoting as is.  Otherwise, the parameters will be quoted (the
 650         default).
 651
 652         An alternative header can be specified in the header argument.  When
 653         the Content-Type header is set, we'll always also add a MIME-Version
 654         header.
 655         """
 656         # BAW: should we be strict?
 657         if not type.count('/') == 1:
 658             raise ValueError
 659         # Set the Content-Type, you get a MIME-Version
 660         if header.lower() == 'content-type':
 661             del self['mime-version']
 662             self['MIME-Version'] = '1.0'
 663         if header not in self:
 664             self[header] = type
 665             return
 666         params = self.get_params(header=header, unquote=requote)
 667         del self[header]
 668         self[header] = type
 669         # Skip the first param; it's the old type.
 670         for p, v in params[1:]:
 671             self.set_param(p, v, header, requote)
 672
 673     def get_filename(self, failobj=None):
 674         """Return the filename associated with the payload if present.
 675
 676         The filename is extracted from the Content-Disposition header's
 677         `filename' parameter, and it is unquoted.  If that header is missing
 678         the `filename' parameter, this method falls back to looking for the
 679         `name' parameter.
 680         """
 681         missing = object()
 682         filename = self.get_param('filename', missing, 'content-disposition')
 683         if filename is missing:
 684             filename = self.get_param('name', missing, 'content-type')
 685         if filename is missing:
 686             return failobj
 687         return utils.collapse_rfc2231_value(filename).strip()
 688
 689     def get_boundary(self, failobj=None):
 690         """Return the boundary associated with the payload if present.
 691
 692         The boundary is extracted from the Content-Type header's `boundary'
 693         parameter, and it is unquoted.
 694         """
 695         missing = object()
 696         boundary = self.get_param('boundary', missing)
 697         if boundary is missing:
 698             return failobj
 699         # RFC 2046 says that boundaries may begin but not end in w/s
 700         return utils.collapse_rfc2231_value(boundary).rstrip()
 701
 702     def set_boundary(self, boundary):
 703         """Set the boundary parameter in Content-Type to 'boundary'.
 704
 705         This is subtly different than deleting the Content-Type header and
 706         adding a new one with a new boundary parameter via add_header().  The
 707         main difference is that using the set_boundary() method preserves the
 708         order of the Content-Type header in the original message.
 709
 710         HeaderParseError is raised if the message has no Content-Type header.
 711         """
 712         missing = object()
 713         params = self._get_params_preserve(missing, 'content-type')
 714         if params is missing:
 715             # There was no Content-Type header, and we don't know what type
 716             # to set it to, so raise an exception.
 717             raise errors.HeaderParseError('No Content-Type header found')
 718         newparams = []
 719         foundp = False
 720         for pk, pv in params:
 721             if pk.lower() == 'boundary':
 722                 newparams.append(('boundary', '"%s"' % boundary))
 723                 foundp = True
 724             else:
 725                 newparams.append((pk, pv))
 726         if not foundp:
 727             # The original Content-Type header had no boundary attribute.
 728             # Tack one on the end.  BAW: should we raise an exception
 729             # instead???
 730             newparams.append(('boundary', '"%s"' % boundary))
 731         # Replace the existing Content-Type header with the new value
 732         newheaders = []
 733         for h, v in self._headers:
 734             if h.lower() == 'content-type':
 735                 parts = []
 736                 for k, v in newparams:
 737                     if v == '':
 738                         parts.append(k)
 739                     else:
 740                         parts.append('%s=%s' % (k, v))
 741                 newheaders.append((h, SEMISPACE.join(parts)))
 742
 743             else:
 744                 newheaders.append((h, v))
 745         self._headers = newheaders
 746
 747     def get_content_charset(self, failobj=None):
 748         """Return the charset parameter of the Content-Type header.
 749
 750         The returned string is always coerced to lower case.  If there is no
 751         Content-Type header, or if that header has no charset parameter,
 752         failobj is returned.
 753         """
 754         missing = object()
 755         charset = self.get_param('charset', missing)
 756         if charset is missing:
 757             return failobj
 758         if isinstance(charset, tuple):
 759             # RFC 2231 encoded, so decode it, and it better end up as ascii.
 760             pcharset = charset[0] or 'us-ascii'
 761             try:
 762                 # LookupError will be raised if the charset isn't known to
 763                 # Python.  UnicodeError will be raised if the encoded text
 764                 # contains a character not in the charset.
 765                 charset = unicode(charset[2], pcharset).encode('us-ascii')
 766             except (LookupError, UnicodeError):
 767                 charset = charset[2]
 768         # charset character must be in us-ascii range
 769         try:
 770             if isinstance(charset, str):
 771                 charset = unicode(charset, 'us-ascii')
 772             charset = charset.encode('us-ascii')
 773         except UnicodeError:
 774             return failobj
 775         # RFC 2046, $4.1.2 says charsets are not case sensitive
 776         return charset.lower()
 777
 778     def get_charsets(self, failobj=None):
 779         """Return a list containing the charset(s) used in this message.
 780
 781         The returned list of items describes the Content-Type headers'
 782         charset parameter for this message and all the subparts in its
 783         payload.
 784
 785         Each item will either be a string (the value of the charset parameter
 786         in the Content-Type header of that part) or the value of the
 787         'failobj' parameter (defaults to None), if the part does not have a
 788         main MIME type of "text", or the charset is not defined.
 789
 790         The list will contain one string for each part of the message, plus
 791         one for the container message (i.e. self), so that a non-multipart
 792         message will still return a list of length 1.
 793         """
 794         return [part.get_content_charset(failobj) for part in self.walk()]
 795
 796     # I.e. def walk(self): ...
 797     from email.iterators import walk