output.txt

 -------> 
[]
'Content-Type' 'image/png'
'Content-Length' '89142'
'X-AppEngine-Upload-Creation' '2018-06-13 23:05:52.565812'
'X-AppEngine-Cloud-Storage-Object' '/gs/eap-dokumente/-/common/dokumente/L2Fw='


 -------> 8bit
[]
'Content-Type' 'image/png'
'Content-Length' '89142'
'X-AppEngine-Upload-Creation' '2018-06-13 23:05:52.565812'
'X-AppEngine-Cloud-Storage-Object' '/gs/eap-dokumente/-/common/dokumente/L2Fw='


 -------> 7bit
[]
'Content-Type' 'image/png'
'Content-Length' '89142'
'X-AppEngine-Upload-Creation' '2018-06-13 23:05:52.565812'
'X-AppEngine-Cloud-Storage-Object' '/gs/eap-dokumente/-/common/dokumente/L2Fw='


 -------> binary
[]
'Content-Type' 'image/png'
'Content-Length' '89142'
'X-AppEngine-Upload-Creation' '2018-06-13 23:05:52.565812'
'X-AppEngine-Cloud-Storage-Object' '/gs/eap-dokumente/-/common/dokumente/L2Fw='


 -------> quoted-printable
[]
'Content-Type' 'image/png'
'Content-Length' '89142'
'X-AppEngine-Upload-Creation' '2018-06-13 23:05:52.565812'
'X-AppEngine-Cloud-Storage-Object' '/gs/eap-dokumente/-/common/dokumente/L2FwcGhvc3RpbmdfZ2xvYmFsL2Jsb2JzL0FFbkIyVXBoTDg3TzhjLUdfOWpISk5VMGJmbER6VGJJdXZOcGxwS2g4STBtTEgtQzBEazJGSU5iSVk4Z1JSckc3TVhZVjVtcXpua2FuUUVTM2pva1R4MWtycVFuTTN2R213LnExRFUxd045RWZpWkdoSlU'
'Content-MD5' 'NjVlNWE4NGRhNTY4YTRjNWQyZmZjOTY4YTkzNzA3MjU='
'Content-Disposition' 'form-data; name=f; \r\n\tfilename="1EC81BF811517A50385D59B9DD05F1BABBF8C7CB446AC99EFBC3FC7CBB2BA1D1.png"'

test_encoding.py

data = 'Content-Type: image/png\r\nContent-Length: 89142\r\nX-AppEngine-Upload-Creation: 2018-06-13 23:05:52.565812\r\nX-AppEngine-Cloud-Storage-Object: /gs/eap-dokumente/-/common/dokumente/L2Fw=\r\ncGhvc3RpbmdfZ2xvYmFsL2Jsb2JzL0FFbkIyVXBoTDg3TzhjLUdfOWpISk5VMGJmbER6VGJJdXZ=\r\nOcGxwS2g4STBtTEgtQzBEazJGSU5iSVk4Z1JSckc3TVhZVjVtcXpua2FuUUVTM2pva1R4MWtycV=\r\nFuTTN2R213LnExRFUxd045RWZpWkdoSlU\r\nContent-MD5: NjVlNWE4NGRhNTY4YTRjNWQyZmZjOTY4YTkzNzA3MjU=3D\r\nContent-Disposition: form-data; name=3Df;=20\r\n\tfilename=3D"1EC81BF811517A50385D59B9DD05F1BABBF8C7CB446AC99EFBC3FC7CBB2BA1=\r\nD1.png"\r\n\r\n'

import email.message


def parse(encoding):
    message = email.message.Message()
    message.add_header('content-transfer-encoding', encoding)
    # Content-Transfer-Encoding
    message.set_payload(data)
    payload = message.get_payload(decode=True)
    return email.message_from_string(payload)

for coding in ['', '8bit', '7bit', 'binary', 'quoted-printable']:
    print "\n\n ------->", coding
    msg = parse(coding)
    print msg.defects
    for k, v in msg.items():
        print repr(k), repr(v)