How to Decode Base64 Data in Python

Python: Decoding base64 encoded strings

It would appear that the final A is superfluous:

In [4]: base64.b64decode('aHR0cDovLzR1ZnJlZS50ay9tZWRpYTcyMzY0Ni9mdWVuZi8wMzYubXAz')
Out[4]: 'http://4ufree.tk/media723646/fuenf/036.mp3'

Encode and Decode with Base64 and Pickle

Call data.decode() or the equivalent str(data, encoding='utf-8') to convert the bytes to a valid base64-encoded string:

# publishJson = json.dumps({"payload": str(data)})     # -
publishJson = json.dumps({"payload": data.decode())})  # +

From https://docs.python.org/3/library/stdtypes.html#str:

Passing a bytes object to str() without the encoding or errors arguments falls under the first case of returning the informal string representation

print(data)                 #  b'gASVLwAAAAAAAAB9lCiMCHRlc3RLZXkxlF2UKEsBSwJLA2WMCHRlc3RLZXkylF2UKEsESwVLBmV1Lg=='
print(repr(data))           #  b'gASVLwAAAAAAAAB9lCiMCHRlc3RLZXkxlF2UKEsBSwJLA2WMCHRlc3RLZXkylF2UKEsESwVLBmV1Lg=='

print(str(data))            #  b'gASVLwAAAAAAAAB9lCiMCHRlc3RLZXkxlF2UKEsBSwJLA2WMCHRlc3RLZXkylF2UKEsESwVLBmV1Lg=='
print(repr(str(data)))      # "b'gASVLwAAAAAAAAB9lCiMCHRlc3RLZXkxlF2UKEsBSwJLA2WMCHRlc3RLZXkylF2UKEsESwVLBmV1Lg=='"

print(data.decode())        #    gASVLwAAAAAAAAB9lCiMCHRlc3RLZXkxlF2UKEsBSwJLA2WMCHRlc3RLZXkylF2UKEsESwVLBmV1Lg==
print(repr(data.decode()))  #   'gASVLwAAAAAAAAB9lCiMCHRlc3RLZXkxlF2UKEsBSwJLA2WMCHRlc3RLZXkylF2UKEsESwVLBmV1Lg=='

How to decode base64 in python3

Base64 needs a string with length multiple of 4. If the string is short, it is padded with 1 to 3 =.

import base64
code = "YWRtaW46MjAyY2I5NjJhYzU5MDc1Yjk2NGIwNzE1MmQyMzRiNzA="
base64.b64decode(code)
# b'admin:202cb962ac59075b964b07152d234b70'

Decoding (Base64 encoded data with type conversion to string by python type casting) to byte array in JAVA

Maybe you should provide a snippet which can be used to reproduce your issue.

Following snippets are working

import base64
f = open("monitor-1.png", "rb")
data = f.read()
encoded_string = str(base64.b64encode(data))
print(encoded_string)
f.close()

output

b'iVBORw0KGgoAAAANSUhEUgAAAAIAAAABAQMAAADO7O3JAAAABlBMVEUAAAD///+l2Z/dAAAACklEQVQI12NoAAAAggCB3UNq9AAAAABJRU5ErkJggg=='

using the Base64 encoded string in Java jshell

jshell> byte[] bytes = Base64.getDecoder().decode("iVBORw0KGgoAAAANSUhEUgAAAAIAAAABAQMAAADO7O3JAAAABlBMVEUAAAD///+l2Z/dAAAACklEQVQI12NoAAAAggCB3UNq9AAAAABJRU5ErkJggg==")
bytes ==> byte[85] { -119, 80, 78, 71, 13, 10, 26, 10, 0, 0 ... 8, 68, -82, 66, 96, -126 }

jshell> Files.write(Paths.get("out.png"), bytes)
$2 ==> out.png

creates the file out.png

The file monitor-1.png and out.png are equal

$ md5sum monitor-1.png out.png 
49b0cecce3c3ce0966afd6c13b03a4b5  monitor-1.png
49b0cecce3c3ce0966afd6c13b03a4b5  out.png

How to convert from Base64 to string Python 3.2

A string is already 'decoded', thus the str class has no 'decode' function.Thus:

AttributeError: type object 'str' has no attribute 'decode'

If you want to decode a byte array and turn it into a string call:

the_thing.decode(encoding)

If you want to encode a string (turn it into a byte array) call:

the_string.encode(encoding)

In terms of the base 64 stuff:
Using 'base64' as the value for encoding above yields the error:

LookupError: unknown encoding: base64

Open a console and type in the following:

import base64
help(base64)

You will see that base64 has two very handy functions, namely b64decode and b64encode. b64 decode returns a byte array and b64encode requires a bytes array.

To convert a string into it's base64 representation you first need to convert it to bytes. I like utf-8 but use whatever encoding you need...

import base64
def stringToBase64(s):
    return base64.b64encode(s.encode('utf-8'))

def base64ToString(b):
    return base64.b64decode(b).decode('utf-8')

Find, decode and replace all base64 values in text file

you already have it, you just need the small pieces:

pattern: r'data=([^&]+?)"' will match anything after data= and before "

>>> pat = r'data=([^&]+?)"'
>>> line = '<a href="http://blahblah.org/kb/getattachment.php?data=NHxUb3Bjb25fZGF0YS1kb3dubG9hZF9ob3d0by5wZGY=">attached file</a>'
>>> decodeString = re.search(pat,line).group(1) #because the b64 string is capture by grouping, we only want group(1)
>>> decodeString
'NHxUb3Bjb25fZGF0YS1kb3dubG9hZF9ob3d0by5wZGY='

you can then use str.replace() method as well as base64.b64decode() method to finish the rest. I dont want to just write your code for you but this should give you a good idea of where to go.

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