I followed an example from the documentation of how to use Base64 encoding in Python:
>>> import base64
>>> encoded = base64.b64encode(b'data to be encoded')
>>> encoded
b'ZGF0YSB0byBiZSBlbmNvZGVk'
But, if I try to encode a normal string - leaving out the leading b:
>>> encoded = base64.b64encode('data to be encoded')
I get a TypeError. In older versions of Python it looked like:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "C:\Python32\lib\base64.py", line 56, in b64encode
raise TypeError("expected bytes, not %s" % s.__class__.__name__)
TypeError: expected bytes, not str
In more recent versions it might look like:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/lib/python3.12/base64.py", line 58, in b64encode
encoded = binascii.b2a_base64(s, newline=False)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: a bytes-like object is required, not 'str'
Why does this happen?
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.