To decode base64 format you need to pass a bytes object to the base64.decodebytes function:

import base64

t = "AAADccB6OAAAAAAAAAAAAAAAAAAAAAAAAAA8WIEAAAAAAACxAAAAHgAACAAADAzBmAQwzoMABgCI AiTSSACCCAAhIAAAiAEMTMgMJibMsZuGeijn4BnI+YeQ0OMOKAACAgAKAABQAAQEABQAAAAAAAAA AA=="
t = t.encode("ascii")

decoded = base64.decodebytes(t)

print(decoded)
print(len(decoded)*8)

I get the following:

b'\x00\x00\x03q\xc0z8\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00<X\x81\x00\x00\x00\x00\x00\x00\xb1\x00\x00\x00\x1e\x00\x00\x08\x00\x00\x0c\x0c\xc1\x98\x040\xce\x83\x00\x06\x00\x88\x02$\xd2H\x00\x82\x08\x00! \x00\x00\x88\x01\x0cL\xc8\x0c&&\xcc\xb1\x9b\x86z(\xe7\xe0\x19\xc8\xf9\x87\x90\xd0\xe3\x0e(\x00\x02\x02\x00\n\x00\x00P\x00\x04\x04\x00\x14\x00\x00\x00\x00\x00\x00\x00\x00'
920

So 920 bits as expected.

To get data as binary just iterate on the bytes and convert to binary using format and zero-padding to 8 digits (bin adds a 0b header so it's not suitable), and join the strings together:

print("".join(["{:08b}".format(x) for x in decoded]))

results in:

00000000000000000000001101110001110000000111101000111000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000011110001011000100000010000000000000000000000000000000000000000000000001011000100000000000000000000000000011110000000000000000000001000000000000000000000001100000011001100000110011000000001000011000011001110100000110000000000000110000000001000100000000010001001001101001001001000000000001000001000001000000000000010000100100000000000000000000010001000000000010000110001001100110010000000110000100110001001101100110010110001100110111000011001111010001010001110011111100000000110011100100011111001100001111001000011010000111000110000111000101000000000000000001000000010000000000000101000000000000000000101000000000000000001000000010000000000000101000000000000000000000000000000000000000000000000000000000000000000

(which is 920 chars, as expected)

Hence the open's binary mode you have to use 'wb' else it gets saved as "text" basically.

import base64
# base64FileData  <= the base64 file data
fileData = base64.urlsafe_b64decode(base64FileData.encode('UTF-8'))
with open('thefilename.pdf', 'wb') as theFile:
    theFile.write(fileData)

You must first decode your string

from base64 import decodestring

Then you can use format(ord(x), "b") to produce a binary representation.

my_string = "cw=="
print "".join(format(ord(x), "b") for x in decodestring(my_string))
>> '1110011'

Depending on how you represent the value 0b100

>>> import struct
>>> val = 0b100
>>> print struct.pack('I', val).encode('base64')
BAAAAA==

This will turn your value into a 4-byte integer in native endianness, and encode that value into base64. You need to specify the width of your data as base64 is really made for representing binary data in printable characters.

You can typically encode data as a string of bytes via struct's functions, and then encode into base64. Ensure you're using the same data layout and endianess when decoding.

just two lines could solve this problem:

import base64
base64_code = "VER30QHI30JFOIAIO3020085723F"  # this is just an example
 
img_data = base64_code.encode()
content = base64.b64decode(img_data)

with open('/path/to/your/image.jpg', 'wb') as fw:
    fw.write(content)
print(content)

then you could check the image bytes.

From the base64 package doc:

base64.encodestring:

"Encode the bytes-like object s, which can contain arbitrary binary data, and return bytes containing the base64-encoded data, with newlines (b"\n") inserted after every 76 bytes of output, and ensuring that there is a trailing newline, as per RFC 2045 (MIME)."

You want to use

base64.b64encode:

"Encode the bytes-like object s using Base64 and return the encoded bytes."

Example:

import base64

with open("test.zip", "rb") as f:
    encodedZip = base64.b64encode(f.read())
    print(encodedZip.decode())

The decode() will convert the binary string to text.