email.message.Message: Representing an email message using thecompat32 API

TheMessage class is very similar to theEmailMessage class, without the methods added by thatclass, and with the default behavior of certain other methods being slightlydifferent. We also document here some methods that, while supported by theEmailMessage class, are not recommended unless you aredealing with legacy code.

The philosophy and structure of the two classes is otherwise the same.

This document describes the behavior under the default (forMessage)policyCompat32. If you are going to use another policy,you should be using theEmailMessage class instead.

An email message consists ofheaders and apayload. Headers must beRFC 5322 style names and values, where the field name and value areseparated by a colon. The colon is not part of either the field name or thefield value. The payload may be a simple text message, or a binary object, ora structured sequence of sub-messages each with their own set of headers andtheir own payload. The latter type of payload is indicated by the messagehaving a MIME type such asmultipart/* ormessage/rfc822.

The conceptual model provided by aMessage object is that of anordered dictionary of headers with additional methods for accessing bothspecialized information from the headers, for accessing the payload, forgenerating a serialized version of the message, and for recursively walkingover the object tree. Note that duplicate headers are supported but specialmethods must be used to access them.

TheMessage pseudo-dictionary is indexed by the header names, whichmust be ASCII values. The values of the dictionary are strings that aresupposed to contain only ASCII characters; there is some special handling fornon-ASCII input, but it doesn't always produce the correct results. Headersare stored and returned in case-preserving form, but field names are matchedcase-insensitively. There may also be a single envelope header, also known astheUnix-From header or theFrom_ header. Thepayload is either astring or bytes, in the case of simple message objects, or a list ofMessage objects, for MIME container documents (e.g.multipart/* andmessage/rfc822).

Here are the methods of theMessage class:

classemail.message.Message(policy=compat32)

Ifpolicy is specified (it must be an instance of apolicyclass) use the rules it specifies to update and serialize the representationof the message. Ifpolicy is not set, use thecompat32 policy, which maintains backward compatibility withthe Python 3.2 version of the email package. For more information see thepolicy documentation.

在 3.3 版的變更:新增policy 關鍵字引數。

as_string(unixfrom=False,maxheaderlen=0,policy=None)

Return the entire message flattened as a string. When optionalunixfromis true, the envelope header is included in the returned string.unixfrom defaults toFalse. For backward compatibility reasons,maxheaderlen defaults to0, so if you want a different value youmust override it explicitly (the value specified formax_line_length inthe policy will be ignored by this method). Thepolicy argument may beused to override the default policy obtained from the message instance.This can be used to control some of the formatting produced by themethod, since the specifiedpolicy will be passed to theGenerator.

Flattening the message may trigger changes to theMessage ifdefaults need to be filled in to complete the transformation to a string(for example, MIME boundaries may be generated or modified).

Note that this method is provided as a convenience and may not alwaysformat the message the way you want. For example, by default it doesnot do the mangling of lines that begin withFrom that isrequired by the Unix mbox format. For more flexibility, instantiate aGenerator instance and use itsflatten() method directly. For example:

fromioimportStringIOfromemail.generatorimportGeneratorfp=StringIO()g=Generator(fp,mangle_from_=True,maxheaderlen=60)g.flatten(msg)text=fp.getvalue()

If the message object contains binary data that is not encoded accordingto RFC standards, the non-compliant data will be replaced by unicode"unknown character" code points. (See alsoas_bytes() andBytesGenerator.)

在 3.4 版的變更:新增policy 關鍵字引數。

__str__()

Equivalent toas_string(). Allowsstr(msg) to produce astring containing the formatted message.

as_bytes(unixfrom=False,policy=None)

Return the entire message flattened as a bytes object. When optionalunixfrom is true, the envelope header is included in the returnedstring.unixfrom defaults toFalse. Thepolicy argument may beused to override the default policy obtained from the message instance.This can be used to control some of the formatting produced by themethod, since the specifiedpolicy will be passed to theBytesGenerator.

Flattening the message may trigger changes to theMessage ifdefaults need to be filled in to complete the transformation to a string(for example, MIME boundaries may be generated or modified).

Note that this method is provided as a convenience and may not alwaysformat the message the way you want. For example, by default it doesnot do the mangling of lines that begin withFrom that isrequired by the Unix mbox format. For more flexibility, instantiate aBytesGenerator instance and use itsflatten() method directly.For example:

fromioimportBytesIOfromemail.generatorimportBytesGeneratorfp=BytesIO()g=BytesGenerator(fp,mangle_from_=True,maxheaderlen=60)g.flatten(msg)text=fp.getvalue()

在 3.4 版被加入.

__bytes__()

Equivalent toas_bytes(). Allowsbytes(msg) to produce abytes object containing the formatted message.

在 3.4 版被加入.

is_multipart()

ReturnTrue if the message's payload is a list ofsub-Message objects, otherwise returnFalse. Whenis_multipart() returnsFalse, the payload should be a stringobject (which might be a CTE encoded binary payload). (Note thatis_multipart() returningTrue does not necessarily mean that"msg.get_content_maintype() == 'multipart'" will return theTrue.For example,is_multipart will returnTrue when theMessage is of typemessage/rfc822.)

set_unixfrom(unixfrom)

Set the message's envelope header tounixfrom, which should be a string.

get_unixfrom()

Return the message's envelope header. Defaults toNone if theenvelope header was never set.

attach(payload)

Add the givenpayload to the current payload, which must beNone ora list ofMessage objects before the call. After the call, thepayload will always be a list ofMessage objects. If you want toset the payload to a scalar object (e.g. a string), useset_payload() instead.

This is a legacy method. On theEmailMessage class its functionality isreplaced byset_content() and therelatedmake andadd methods.

get_payload(i=None,decode=False)

Return the current payload, which will be a list ofMessage objects whenis_multipart() isTrue, or astring whenis_multipart() isFalse. If the payload is a listand you mutate the list object, you modify the message's payload in place.

With optional argumenti,get_payload() will return thei-thelement of the payload, counting from zero, ifis_multipart() isTrue. AnIndexError will be raised ifi is less than 0 orgreater than or equal to the number of items in the payload. If thepayload is a string (i.e.is_multipart() isFalse) andi isgiven, aTypeError is raised.

Optionaldecode is a flag indicating whether the payload should bedecoded or not, according to theContent-Transfer-Encodingheader. WhenTrue and the message is not a multipart, the payload willbe decoded if this header's value isquoted-printable orbase64.If some other encoding is used, orContent-Transfer-Encodingheader is missing, the payload isreturned as-is (undecoded). In all cases the returned value is binarydata. If the message is a multipart and thedecode flag isTrue,thenNone is returned. If the payload is base64 and it was notperfectly formed (missing padding, characters outside the base64alphabet), then an appropriate defect will be added to the message'sdefect property (InvalidBase64PaddingDefect orInvalidBase64CharactersDefect, respectively).

Whendecode isFalse (the default) the body is returned as a stringwithout decoding theContent-Transfer-Encoding. However,for aContent-Transfer-Encoding of 8bit, an attempt is madeto decode the original bytes using thecharset specified by theContent-Type header, using thereplace error handler.If nocharset is specified, or if thecharset given is notrecognized by the email package, the body is decoded using the defaultASCII charset.

This is a legacy method. On theEmailMessage class its functionality isreplaced byget_content() anditer_parts().

set_payload(payload,charset=None)

Set the entire message object's payload topayload. It is the client'sresponsibility to ensure the payload invariants. Optionalcharset setsthe message's default character set; seeset_charset() for details.

This is a legacy method. On theEmailMessage class its functionality isreplaced byset_content().

set_charset(charset)

Set the character set of the payload tocharset, which can either be aCharset instance (seeemail.charset), astring naming a character set, orNone. If it is a string, it willbe converted to aCharset instance. IfcharsetisNone, thecharset parameter will be removed from theContent-Type header (the message will not be otherwisemodified). Anything else will generate aTypeError.

If there is no existingMIME-Version header one will beadded. If there is no existingContent-Type header, onewill be added with a value oftext/plain. Whether theContent-Type header already exists or not, itscharsetparameter will be set tocharset.output_charset. Ifcharset.input_charset andcharset.output_charset differ, the payloadwill be re-encoded to theoutput_charset. If there is no existingContent-Transfer-Encoding header, then the payload will betransfer-encoded, if needed, using the specifiedCharset, and a header with the appropriate valuewill be added. If aContent-Transfer-Encoding headeralready exists, the payload is assumed to already be correctly encodedusing thatContent-Transfer-Encoding and is not modified.

This is a legacy method. On theEmailMessage class its functionality isreplaced by thecharset parameter of theemail.emailmessage.EmailMessage.set_content() method.

get_charset()

Return theCharset instance associated with themessage's payload.

This is a legacy method. On theEmailMessage class it always returnsNone.

The following methods implement a mapping-like interface for accessing themessage'sRFC 2822 headers. Note that there are some semantic differencesbetween these methods and a normal mapping (i.e. dictionary) interface. Forexample, in a dictionary there are no duplicate keys, but here there may beduplicate message headers. Also, in dictionaries there is no guaranteedorder to the keys returned bykeys(), but in aMessage object,headers are always returned in the order they appeared in the originalmessage, or were added to the message later. Any header deleted and thenre-added are always appended to the end of the header list.

These semantic differences are intentional and are biased toward maximalconvenience.

Note that in all cases, any envelope header present in the message is notincluded in the mapping interface.

In a model generated from bytes, any header values that (in contravention ofthe RFCs) contain non-ASCII bytes will, when retrieved through thisinterface, be represented asHeader objects witha charset ofunknown-8bit.

__len__()

Return the total number of headers, including duplicates.

__contains__(name)

ReturnTrue if the message object has a field namedname. Matching isdone case-insensitively andname should not include the trailing colon.Used for thein operator, e.g.:

if'message-id'inmyMessage:print('Message-ID:',myMessage['message-id'])
__getitem__(name)

Return the value of the named header field.name should not include thecolon field separator. If the header is missing,None is returned; aKeyError is never raised.

Note that if the named field appears more than once in the message'sheaders, exactly which of those field values will be returned isundefined. Use theget_all() method to get the values of all theextant named headers.

__setitem__(name,val)

Add a header to the message with field namename and valueval. Thefield is appended to the end of the message's existing fields.

Note that this doesnot overwrite or delete any existing header with the samename. If you want to ensure that the new header is the only one present in themessage with field namename, delete the field first, e.g.:

delmsg['subject']msg['subject']='Python roolz!'
__delitem__(name)

Delete all occurrences of the field with namename from the message'sheaders. No exception is raised if the named field isn't present in theheaders.

keys()

Return a list of all the message's header field names.

values()

Return a list of all the message's field values.

items()

Return a list of 2-tuples containing all the message's field headers andvalues.

get(name,failobj=None)

Return the value of the named header field. This is identical to__getitem__() except that optionalfailobj is returned if thenamed header is missing (defaults toNone).

Here are some additional useful methods:

get_all(name,failobj=None)

Return a list of all the values for the field namedname. If there areno such named headers in the message,failobj is returned (defaults toNone).

add_header(_name,_value,**_params)

Extended header setting. This method is similar to__setitem__()except that additional header parameters can be provided as keywordarguments._name is the header field to add and_value is theprimary value for the header.

For each item in the keyword argument dictionary_params, the key istaken as the parameter name, with underscores converted to dashes (sincedashes are illegal in Python identifiers). Normally, the parameter willbe added askey="value" unless the value isNone, in which caseonly the key will be added. If the value contains non-ASCII characters,it can be specified as a three tuple in the format(CHARSET,LANGUAGE,VALUE), whereCHARSET is a string naming thecharset to be used to encode the value,LANGUAGE can usually be settoNone or the empty string (seeRFC 2231 for other possibilities),andVALUE is the string value containing non-ASCII code points. Ifa three tuple is not passed and the value contains non-ASCII characters,it is automatically encoded inRFC 2231 format using aCHARSETofutf-8 and aLANGUAGE ofNone.

以下是個範例：

msg.add_header('Content-Disposition','attachment',filename='bud.gif')

This will add a header that looks like

Content-Disposition:attachment;filename="bud.gif"

An example with non-ASCII characters:

msg.add_header('Content-Disposition','attachment',filename=('iso-8859-1','','Fußballer.ppt'))

Which produces

Content-Disposition:attachment;filename*="iso-8859-1''Fu%DFballer.ppt"
replace_header(_name,_value)

Replace a header. Replace the first header found in the message thatmatches_name, retaining header order and field name case. If nomatching header was found, aKeyError is raised.

get_content_type()

Return the message's content type. The returned string is coerced tolower case of the formmaintype/subtype. If there was noContent-Type header in the message the default type as givenbyget_default_type() will be returned. Since according toRFC 2045, messages always have a default type,get_content_type()will always return a value.

RFC 2045 defines a message's default type to betext/plainunless it appears inside amultipart/digest container, inwhich case it would bemessage/rfc822. If theContent-Type header has an invalid type specification,RFC 2045 mandates that the default type betext/plain.

get_content_maintype()

Return the message's main content type. This is themaintypepart of the string returned byget_content_type().

get_content_subtype()

Return the message's sub-content type. This is thesubtypepart of the string returned byget_content_type().

get_default_type()

Return the default content type. Most messages have a default contenttype oftext/plain, except for messages that are subparts ofmultipart/digest containers. Such subparts have a defaultcontent type ofmessage/rfc822.

set_default_type(ctype)

Set the default content type.ctype should either betext/plain ormessage/rfc822, although this is notenforced. The default content type is not stored in theContent-Type header.

get_params(failobj=None,header='content-type',unquote=True)

Return the message'sContent-Type parameters, as a list.The elements of the returned list are 2-tuples of key/value pairs, assplit on the'=' sign. The left hand side of the'=' is the key,while the right hand side is the value. If there is no'=' sign inthe parameter the value is the empty string, otherwise the value is asdescribed inget_param() and is unquoted if optionalunquote isTrue (the default).

Optionalfailobj is the object to return if there is noContent-Type header. Optionalheader is the header tosearch instead ofContent-Type.

This is a legacy method. On theEmailMessage class its functionality isreplaced by theparams property of the individual header objectsreturned by the header access methods.

get_param(param,failobj=None,header='content-type',unquote=True)

Return the value of theContent-Type header's parameterparam as a string. If the message has noContent-Typeheader or if there is no such parameter, thenfailobj is returned(defaults toNone).

Optionalheader if given, specifies the message header to use instead ofContent-Type.

Parameter keys are always compared case insensitively. The return valuecan either be a string, or a 3-tuple if the parameter wasRFC 2231encoded. When it's a 3-tuple, the elements of the value are of the form(CHARSET,LANGUAGE,VALUE). Note that bothCHARSET andLANGUAGE can beNone, in which case you should considerVALUEto be encoded in theus-ascii charset. You can usually ignoreLANGUAGE.

If your application doesn't care whether the parameter was encoded as inRFC 2231, you can collapse the parameter value by callingemail.utils.collapse_rfc2231_value(), passing in the return valuefromget_param(). This will return a suitably decoded Unicodestring when the value is a tuple, or the original string unquoted if itisn't. For example:

rawparam=msg.get_param('foo')param=email.utils.collapse_rfc2231_value(rawparam)

In any case, the parameter value (either the returned string, or theVALUE item in the 3-tuple) is always unquoted, unlessunquote is settoFalse.

This is a legacy method. On theEmailMessage class its functionality isreplaced by theparams property of the individual header objectsreturned by the header access methods.

set_param(param,value,header='Content-Type',requote=True,charset=None,language='',replace=False)

Set a parameter in theContent-Type header. If theparameter already exists in the header, its value will be replaced withvalue. If theContent-Type header as not yet been definedfor this message, it will be set totext/plain and the newparameter value will be appended as perRFC 2045.

Optionalheader specifies an alternative header toContent-Type, and all parameters will be quoted as necessaryunless optionalrequote isFalse (the default isTrue).

If optionalcharset is specified, the parameter will be encodedaccording toRFC 2231. Optionallanguage specifies the RFC 2231language, defaulting to the empty string. Bothcharset andlanguageshould be strings.

Ifreplace isFalse (the default) the header is moved to theend of the list of headers. Ifreplace isTrue, the headerwill be updated in place.

在 3.4 版的變更:replace keyword was added.

del_param(param,header='content-type',requote=True)

Remove the given parameter completely from theContent-Typeheader. The header will be re-written in place without the parameter orits value. All values will be quoted as necessary unlessrequote isFalse (the default isTrue). Optionalheader specifies analternative toContent-Type.

set_type(type,header='Content-Type',requote=True)

Set the main type and subtype for theContent-Typeheader.type must be a string in the formmaintype/subtype,otherwise aValueError is raised.

This method replaces theContent-Type header, keeping allthe parameters in place. Ifrequote isFalse, this leaves theexisting header's quoting as is, otherwise the parameters will be quoted(the default).

An alternative header can be specified in theheader argument. When theContent-Type header is set aMIME-Versionheader is also added.

This is a legacy method. On theEmailMessage class its functionality isreplaced by themake_ andadd_ methods.

get_filename(failobj=None)

Return the value of thefilename parameter of theContent-Disposition header of the message. If the headerdoes not have afilename parameter, this method falls back to lookingfor thename parameter on theContent-Type header. Ifneither is found, or the header is missing, thenfailobj is returned.The returned string will always be unquoted as peremail.utils.unquote().

get_boundary(failobj=None)

Return the value of theboundary parameter of theContent-Type header of the message, orfailobj if eitherthe header is missing, or has noboundary parameter. The returnedstring will always be unquoted as peremail.utils.unquote().

set_boundary(boundary)

Set theboundary parameter of theContent-Type header toboundary.set_boundary() will always quoteboundary ifnecessary. AHeaderParseError is raised if themessage object has noContent-Type header.

Note that using this method is subtly different than deleting the oldContent-Type header and adding a new one with the newboundary viaadd_header(), becauseset_boundary() preservesthe order of theContent-Type header in the list ofheaders. However, it doesnot preserve any continuation lines which mayhave been present in the originalContent-Type header.

get_content_charset(failobj=None)

Return thecharset parameter of theContent-Type header,coerced to lower case. If there is noContent-Type header, or ifthat header has nocharset parameter,failobj is returned.

Note that this method differs fromget_charset() which returns theCharset instance for the default encoding of the message body.

get_charsets(failobj=None)

Return a list containing the character set names in the message. If themessage is amultipart, then the list will contain one elementfor each subpart in the payload, otherwise, it will be a list of length 1.

Each item in the list will be a string which is the value of thecharset parameter in theContent-Type header for therepresented subpart. However, if the subpart has noContent-Type header, nocharset parameter, or is not ofthetext main MIME type, then that item in the returned listwill befailobj.

get_content_disposition()

Return the lowercased value (without parameters) of the message'sContent-Disposition header if it has one, orNone. Thepossible values for this method areinline,attachment orNoneif the message followsRFC 2183.

在 3.5 版被加入.

walk()

Thewalk() method is an all-purpose generator which can be used toiterate over all the parts and subparts of a message object tree, indepth-first traversal order. You will typically usewalk() as theiterator in afor loop; each iteration returns the next subpart.

Here's an example that prints the MIME type of every part of a multipartmessage structure:

>>>forpartinmsg.walk():...print(part.get_content_type())multipart/reporttext/plainmessage/delivery-statustext/plaintext/plainmessage/rfc822text/plain

walk iterates over the subparts of any part whereis_multipart() returnsTrue, even thoughmsg.get_content_maintype()=='multipart' may returnFalse. Wecan see this in our example by making use of the_structure debughelper function:

>>>forpartinmsg.walk():...print(part.get_content_maintype()=='multipart',...part.is_multipart())True TrueFalse FalseFalse TrueFalse FalseFalse FalseFalse TrueFalse False>>>_structure(msg)multipart/report    text/plain    message/delivery-status        text/plain        text/plain    message/rfc822        text/plain

Here themessage parts are notmultiparts, but they do containsubparts.is_multipart() returnsTrue andwalk descendsinto the subparts.

Message objects can also optionally contain two instance attributes,which can be used when generating the plain text of a MIME message.

preamble

The format of a MIME document allows for some text between the blank linefollowing the headers, and the first multipart boundary string. Normally,this text is never visible in a MIME-aware mail reader because it fallsoutside the standard MIME armor. However, when viewing the raw text ofthe message, or when viewing the message in a non-MIME aware reader, thistext can become visible.

Thepreamble attribute contains this leading extra-armor text for MIMEdocuments. When theParser discovers some textafter the headers but before the first boundary string, it assigns thistext to the message'spreamble attribute. When theGenerator is writing out the plain textrepresentation of a MIME message, and it finds themessage has apreamble attribute, it will write this text in the areabetween the headers and the first boundary. Seeemail.parser andemail.generator for details.

Note that if the message object has no preamble, thepreamble attributewill beNone.

epilogue

Theepilogue attribute acts the same way as thepreamble attribute,except that it contains text that appears between the last boundary andthe end of the message.

You do not need to set the epilogue to the empty string in order for theGenerator to print a newline at the end of thefile.

defects

Thedefects attribute contains a list of all the problems found whenparsing this message. Seeemail.errors for a detailed descriptionof the possible parsing defects.