Why do I need b to encode a string with Base64

Question

Following this python example  I encode a string as Base64 with    gt  gt  gt  import base64  gt  gt  gt  encoded   base64 b64encode b data to be encoded    gt  gt  gt  encoded b ZGF0YSB0byBiZSBlbmNvZGVk    But  if I leave out the leading b    gt  gt  gt  encoded   base64 b64encode  data to be encoded     I get the following error   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File  C  Python32 lib base64 py   line 56  in b64encode    raise TypeError  expected bytes  not  s    s   class     name       TypeError  expected bytes  not str   Why is this

User · Accepted Answer

base64 encoding takes 8-bit binary byte data and encodes it uses only the characters A-Z, a-z, 0-9, +, /* so it can be transmitted over channels that do not preserve all 8-bits of data, such as email.

Hence, it wants a string of 8-bit bytes. You create those in Python 3 with the b'' syntax.

If you remove the b, it becomes a string. A string is a sequence of Unicode characters. base64 has no idea what to do with Unicode data, it's not 8-bit. It's not really any bits, in fact. :-)

In your second example:

>>> encoded = base64.b64encode('data to be encoded')

All the characters fit neatly into the ASCII character set, and base64 encoding is therefore actually a bit pointless. You can convert it to ascii instead, with

>>> encoded = 'data to be encoded'.encode('ascii')

Or simpler:

>>> encoded = b'data to be encoded'

Which would be the same thing in this case.

* Most base64 flavours may also include a = at the end as padding. In addition, some base64 variants may use characters other than + and /. See the Variants summary table at Wikipedia for an overview.

User · Answer

There is all you need   expected bytes  not str   The leading b makes your string binary   What version of Python do you use  2 x or 3 x   Edit  See http   docs python org release 3 0 1 whatsnew 3 0 html text-vs-data-instead-of-unicode-vs-8-bit for the gory details of strings in Python 3 x

User · Answer

Short Answer You need to push a bytes-like object  bytes  bytearray  etc  to the base64 b64encode   method  Here are two ways   gt  gt  gt  import base64  gt  gt  gt  data   base64 b64encode b data to be encoded    gt  gt  gt  print data  b ZGF0YSB0byBiZSBlbmNvZGVk   Or with a variable   gt  gt  gt  import base64  gt  gt  gt  string    data to be encoded   gt  gt  gt  data   base64 b64encode string encode     gt  gt  gt  print data  b ZGF0YSB0byBiZSBlbmNvZGVk   Why  In Python 3  str objects are not C-style character arrays  so they are not byte arrays   but rather  they are data structures that do not have any inherent encoding  You can encode that string  or interpret it  in a variety of ways  The most common  and default in Python 3  is utf-8  especially since it is backwards compatible with ASCII  although  as are most widely-used encodings   That is what is happening when you take a string and call the  encode   method on it  Python is interpreting the string in utf-8  the default encoding  and providing you the array of bytes that it corresponds to  Base-64 Encoding in Python 3 Originally the question title asked about Base-64 encoding  Read on for Base-64 stuff  base64 encoding takes 6-bit binary chunks and encodes them using the characters A-Z  a-z  0-9            and      some encodings use different characters in place of     and       This is a character encoding that is based off of the mathematical construct of radix-64 or base-64 number system  but they are very different  Base-64 in math is a number system like binary or decimal  and you do this change of radix on the entire number  or  if the radix you re converting from is a power of 2 less than 64  in chunks from right to left  In base64 encoding  the translation is done from left to right  those first 64 characters are why it is called base64 encoding  The 65th     symbol is used for padding  since the encoding pulls 6-bit chunks but the data it is usually meant to encode are 8-bit bytes  so sometimes there are only two or 4 bits in the last chunk  Example   gt  gt  gt  data   b test   gt  gt  gt  for byte in data          print format byte   08b    end  quot   quot       01110100 01100101 01110011 01110100  gt  gt  gt   If you interpret that binary data as a single integer  then this is how you would convert it to base-10 and base-64  table for base-64   base-2   01 110100 011001 010111 001101 110100  base-64 grouping shown  base-10                             1952805748 base-64   B      0      Z      X      N      0  base64 encoding  however  will re-group this data thusly  base-2   011101  000110  010101 110011 011101 00 0000   lt - pad w zeros to make a clean 6-bit chunk base-10      29       6      21     51     29      0 base-64       d       G       V      z      d      A  So   B0ZXN0  is the base-64 version of our binary  mathematically speaking  However  base64 encoding has to do the encoding in the opposite direction  so the raw data is converted to  dGVzdA   and also has a rule to tell other applications how much space is left off at the end  This is done by padding the end with     symbols  So  the base64 encoding of this data is  dGVzdA     with two     symbols to signify two pairs of bits will need to be removed from the end when this data gets decoded to make it match the original data  Let s test this to see if I am being dishonest   gt  gt  gt  encoded   base64 b64encode data   gt  gt  gt  print encoded  b dGVzdA     Why use base64 encoding  Let s say I have to send some data to someone via email  like this data   gt  gt  gt  data   b  x04 x6d x73 x67 x08 x08 x08 x20 x20 x20   gt  gt  gt  print data decode         gt  gt  gt  print data  b  x04msg x08 x08 x08      gt  gt  gt   There are two problems I planted   If I tried to send that email in Unix  the email would send as soon as the  x04 character was read  because that is ASCII for END-OF-TRANSMISSION  Ctrl-D   so the remaining data would be left out of the transmission  Also  while Python is smart enough to escape all of my evil control characters when I print the data directly  when that string is decoded as ASCII  you can see that the  msg  is not there  That is because I used three BACKSPACE characters and three SPACE characters to erase the  msg   Thus  even if I didn t have the EOF character there the end user wouldn t be able to translate from the text on screen to the real  raw data   This is just a demo to show you how hard it can be to simply send raw data  Encoding the data into base64 format gives you the exact same data but in a format that ensures it is safe for sending over electronic media such as email

User · Answer

If the string is Unicode the easiest way is   import base64                                                          a   base64 b64encode bytes u complex string                    utf-8       a  b Y29tcGxleCBzdHJpbmc6IMOxw6HDqcOtw7PDusOR   b   base64 b64decode a  decode  utf-8    ignore                        print b    b  complex string

User · Answer

If the data to be encoded contains  exotic  characters  I think you have to encode in  UTF-8   encoded   base64 b64encode  bytes  data to be encoded    utf-8

[python] Why do I need 'b' to encode a string with Base64?

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