On 8/18/2014 3:16 PM, Alex Willmer wrote:
A challenge, just for fun. Can you speed up this function?
You should give a specification here, with examples. You should perhaps
be using .maketrans and .translate.
import string
charset = set(string.ascii_letters + string.digits + '@_-')
byteseq = [chr(i) for i in xrange(256)]
bytemap = {byte: byte if byte in charset else '+' + byte.encode('hex')
for byte in byteseq}
def plus_encode(s):
"""Encode a unicode string with only ascii letters, digits, _, -, @, +
"""
bytemap_ = bytemap
s_utf8 = s.encode('utf-8')
return ''.join([bytemap[byte] for byte in s_utf8])
On my machine (Ubuntu 14.04, CPython 2.7.6, PyPy 2.2.1) this gets
alex@martha:~$ python -m timeit -s 'import plus_encode'
'plus_encode.plus_encode(u"""qwertyuiop1234567890!"£$%^&*()EURO""")'
100000 loops, best of 3: 2.96 usec per loop
alex@martha:~$ pypy -m timeit -s 'import plus_encode'
'plus_encode.plus_encode(u"""qwertyuiop1234567890!"£$%^&*()EURO""")'
1000000 loops, best of 3: 1.24 usec per loop
Back story:
Last week we needed a custom encoding to store unicode usernames in a config
file that only allowed mixed case ascii, digits, underscore, dash, at-sign and
plus sign. We also wanted to keeping the encoded usernames somewhat human
readable.
My design was utf-8 and a variant of %-escaping, using the plus symbol. So
u'alic EURO 123' would be encoded as b'alic+e2+82+ac123'. This evening as a
learning exercise I've tried to make it fast. This is the result.
This challenge is just for fun. The chosen solution ended up being
def name_encode(s):
return %s_%s' % (s.encode('utf-8').encode('hex'),
re.replace('[A-Za-z0-9]', '', s))
Regards, Alex
--
Terry Jan Reedy
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https://mail.python.org/mailman/listinfo/python-list
