Python 2.7 writing strings elements (character) to a binary file
Question: I am using Python 2.7 to access an API that returns JSON with a single
key="ringtone_file" and an associated value that is an mp3 file encoded for
transport via HTTP. I created a bogus mp3 file consisting of 256 bytes in
order from 0x00 through 0xff and the returned file appears below.

    
    
    {"ringtone_file":"\u0000\u0001\u0002\u0003\u0004\u0005\u0006\u0007\b\t\n\u000b\f\r\u000e\u000f\u0010\u0011\u0012\u0013\u0014\u0015\u0016\u0017\u0018\u0019\u001a\u001b\u001c\u001d\u001e\u001f !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~ ¡¢£¤¥¦§¨©ª«¬­®¯°±²³´µ¶·¸¹º»¼½¾¿ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿ"}
    

I accessed the API using the following code minus exception handing code

    
    
    import requests
    
    response = requests.get(url)
    dict = response.json()
    print dict
    

This yields the following output

    
    
    {u'ringtone_file': u'\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff'}
    

What I desire to do is write each character or hex value of this string to a
file in binary format. I desire the result to be a file of size 256 bytes
where the first byte in the file has value 0 and the last byte has value 255.
I can't change the API. Can someone suggest a reasonable way of accomplishing
this with Python 2.7.

I attempted to do what was obvious to me which was to open a file for writing
in binary mode and then writing the unicode string to the file. The error
message from the codec indicates I can't write values between and including
128 and 255.


Answer: Since the string value is Unicode, you have to encode the string to write it
to a file. The `latin1` codec directly maps to the first 256 Unicode
characters, so use `.encode('latin1')` on the string.

Example:

    
    
    >>> s=u'\x00\x01\x02\xfd\xfe\xff'
    >>> s
    u'\x00\x01\x02\xfd\xfe\xff'       # Unicode string
    >>> s.encode('latin1')
    '\x00\x01\x02\xfd\xfe\xff'        # Now a byte string.
    

