Thursday, December 4, 2014

better translate()

translate is a simple, efficient function for doing fast byte-by-byte replacement on a string in Python.

However, Python Does What is always on the lookout for dangerous alternatives to simple things.  Instead of a function call, isn't it better to mutate global interpreter state so that the same result is achieved as a side-effect of a completely different operation?  (The answer is yes.)

>>> import ctypes
>>> def maketrans(inp, outp):
...    inp = list(inp)
...    outp = list(outp)
...    for aa, bb in zip(inp, outp):  # there's a fun reason single letter variable names are a bad idea here
...       ctypes.memset(ctypes.pythonapi.PyString_AsString(id(aa)), ord(bb), 1)
...
>>> maketrans("jkl", "xyz")
>>> "".join("jkl")
'xyz'

This method also has application to single character variable names that bears further exploration.

2 comments:

  1. Replies
    1. This method changes ALL single character strings in the interpreter. Including variable names.

      You can try it, leads to spectacular crashes.

      Delete