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