As per Wikipedia:

Base64 is a group of similar binary-to-text encoding schemes that represent binary data in an ASCII string format by translating it into a radix-64 representation. The term Base64 originates from a specific MIME content transfer encoding. Each base64 digit represents exactly 6 bits of data. Three 8-bit bytes (i.e., a total of 24 bits) can therefore be represented by four 6-bit base64 digits.

To convert a string in base64 format use below python code:

import base64


text = "pythoncircle.com"
result = base64.b64encode(bytes(text, "utf-8")).decode("ascii")
print(result)

To decode a base64 encoded text into plain text, use below python code:

text = "cHl0aG9uY2lyY2xlLmNvbQ=="
try:
    result = base64.b64decode(bytes(text, "utf-8")).decode("ascii")
    print(result)
except TypeError:
    print("Data not in specified format.")
except:
    print("Conversion not possible.")