how to tell if a string is base64 or not

Question

I have many emails coming in from different sources. they all have attachments, many of them have attachment names in chinese, so these names are converted to base64 by thei

Answer 1

Question: """Also I actually need to know what type of file it is ie .xls or .doc so I do need to decode the filename in order to correctly process the attachment, but as above, seems gb2312 is not supported in jython, know any roundabouts?"""

Data:

Content-Type: application/vnd.ms-excel;
 name="=?gb2312?B?uLGxvmhlbrixsb5nLnhscw==?="

Observations:

(1) The first line indicates Microsoft Excel, so .xls is looking better than .doc

(2)

>>> import base64
>>> base64.b64decode("uLGxvmhlbrixsb5nLnhscw==")
'\xb8\xb1\xb1\xbehen\xb8\xb1\xb1\xbeg.xls'
>>>

(a) The extension appears to be .xls -- no need for a gb2312 codec
(b) If you want a file-system-safe file name, you could use the "-_" variant of base64 OR you could percent-encode it
(c) For what it's worth, the file name is XYhenXYg.xls where X and Y are 2 Chinese characters that together mean "copy" and the remainder are literal ASCII characters.