Question

>>> help(bytearray.count)
Help on method_descriptor:

count(...)
    B.count(sub[, start[, end]]) -> int

    Return the number of non-overlapping occurrences of subsection sub in
    bytes B[start:end].  Optional arguments start and end are interpreted
    as in slice notation.

>>> b = bytearray(b'abcd')
>>> b
bytearray(b'abcd')
>>> b.count('a')
Traceback (most recent call last):
  File "<console>", line 1, in <module>
TypeError: Type str doesn't support the buffer API

Question> How to use count for bytearray?

Answer 1

You pretty clearly need to pass another byte array to b.count:

>>> b.count(b'a')