Member Avatar for M.S.

Hi All

Please some one Help me find out why this code doesn't work:

codes=['zlib', 'zip', 'base64', 'hex', 'utf-8']

def encoder(str, i):
    return str.encode(codes[i])

def decoder(str, i):
    return str.decode(codes[i])

en = encoder('Some string here', 2)
print en
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Dani AI

Generated

A few clarifications and a safe pattern to let the user pick exactly one encoding.

As observed, the original behaviour came from applying every codec in a loop; demonstrated that. was right to point toward the codecs machinery. Two important points that caused confusion here: (1) some names like utf-8 are character encodings, while base64, hex, zlib, zip are byte-transform codecs (they turn bytes into other bytes or ASCII). They are not interchangeable and you must decode with the same codec you used to encode; (2) minimal Python installs (mobile/Py2.2) may not expose every codec, so a runtime check and fallbacks are useful.

A concise, safe approach:

  • keep a small allowed list the program accepts (by name or by index),
  • validate the choice with codecs.lookup and handle LookupError,
  • provide fallbacks using base64 / binascii if a transform codec is missing.

Example pattern:

import codecs
import base64
import binascii

ALLOWED = ['utf-8', 'base64', 'hex', 'zlib', 'zip']

def safe_encode(s, choice):
    # choice can be an index (int/long) or a codec name
    if isinstance(choice, (int, long)):
        name = ALLOWED[choice]
    else:
        name = str(choice)
    if name not in ALLOWED:
        raise ValueError("not allowed")
    try:
        codecs.lookup(name)
    except LookupError:
        if name == 'base64':
            return base64.b64encode(s)
        if name == 'hex':
            return binascii.hexlify(s)
        raise
    return s.encode(name)

Troubleshooting tips:

  • If LookupError occurs, check Python version and available encodings; use codecs.lookup to probe at runtime.
  • Remember: for reversible operations, decode with the same codec you used to encode.
  • On Python 3 the API differs: str.encode returns bytes and bytes.decode is used to get text back.

Further reading on the codecs API and common transform modules is in the official docs: codecs module documentation and base64/binascii.

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All 6 Replies

Member Avatar for Gribouillis

It works for me and python 2.6

codes=['zlib', 'zip', 'base64', 'hex', 'utf-8']

def encoder(str, i):
    return str.encode(codes[i])

def decoder(str, i):
    return str.decode(codes[i])

thing = 'Some string here'
for i, k in enumerate(codes):
    en = encoder(thing, i)
    assert thing == decoder(en, i)
    
print "success"
Member Avatar for M.S.

Thanks Gribouillis,
Now it works, but it en/decodes the string in all encodings.
I want to select the encoding freely, for example, something like this:

en1 = encoder('String One', 2)# for base64
en2 = encoder('String Two', 3)# for hex
#en3 = ....
#and so on
Edited by M.S. because: n/a
Member Avatar for Gribouillis

Thanks Gribouillis,
Now it works, but it en/decodes the string in all encodings.
I want to select the encoding freely, for example, something like this:

en1 = encoder('String One', 2)# for base64
en2 = encoder('String Two', 3)# for hex
#en3 = ....
#and so on

I don't understand, doesn't it work as expected ? Please describe the expected output of your program and, if it "doesn't work", why it doesn't produce the expected output, or if it raises an exception, which exception ?

Edited by Gribouillis because: n/a
Member Avatar for TrustyTony

Do not reinvent the wheel, use codecs module: (non-unicode stuff is at the end part of the post)

Member Avatar for M.S.

Thanks again for your reply

as I said the code works, without exceptions.

it gets the value of "thing" and encodes it to all encodings at once.
its ok, but, I want the User select which encoding he needs the string to be encoded. sorry if i cant be more clear(because of language barrier, Im not an English speaker).

in other word:
i want to input encoding selectively:
Input 1: the string I want to Encode or decode
Input 2: one or two of the encodings in list "codes"

Output: Printing out the Encoded/Decoded String

@pyTony: I want to doing this in my mobile python(compatible with Python 2.2), and it has not all of the libraries

Sorry for my bad English

Edited by M.S. because: n/a
Member Avatar for M.S.

Thank you both.
problem solved by tweaking the code u gave to me.

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