I used email.parser.BytesParser for parsing mails. 

In one programm I used parse, because the email was stored in a file.
In a second programm the email was stored in memory as a bytes object.

I created hash values from each parts an compared them, to check if a part is already known to my programs. This works for attachments, but not for html and plain text parts.

Documentation for parsebytes:

Similar to the parse() method, except it takes a bytes-like object instead of a file-like object. Calling this method on a bytes-like object is equivalent to wrapping bytes in a BytesIO instance first and calling parse().

When I read the documentation, I expected that both methods will produce the same output.

The testmail contains 2 mimeparts. One with html and one with plain text.

The parse method with a file and the parse method with bytes-data, wrapped in a BytesIO produces the same hashes. The paesebytes method creates different hashes.

Output of my testprogram:

MD5 sums with parsebytes with bytes data
3f4ee7303378b62f723a8d958797507a
45c72465b931d32c7e700d2dd96f8383
------------------------
MD5 sums with parse and BytesIO with bytes data
fb0599d92750b72c25923139670e5127
9a54b64425b9003a9e6bf199ab6ba603
------------------------
MD5 sums with parse from file
fb0599d92750b72c25923139670e5127
9a54b64425b9003a9e6bf199ab6ba603



Is this an expected behavior or is this an error?