I’ve been working lately with arkon on various projects related to diStorm. One of these projects involved writing a solid Python API around an existing C API. This C API uses a lot of flags as arguments and return values of functions.
Since I want my code to be easy to use in an interactive shell, I’d like to return something that’s not just a number. The obvious solution is to use a Python Enum. There are many implementations going around, most of them equivalent. I’ve got the one I use. What I recently added though, is the SymbolInt:
def SymbolInt(value, name): class _SymbolInt(int): def __str__(self): return name def __repr__(self): return 'SymbolInt(%d, "%s")' % (value, name) def __eq__(self, other): if isinstance(other, str): other = other.lower() return int(self)==other or name.lower() == other def __ne__(self, other): return not self == other return _SymbolInt(value) |
Short, and very much to the point, this makes exploratory API’s much more readable and usable. It is useful as a return value from enum functions as well.
Along with SymbolInt I wrote hexint:
class hexint(long): def __str__(self): return hex(self)[2:-1] __repr__ = __str__ def __repr__(self): return hex(self)[:-1] |
This one makes program addresses readable.
Lastly, here’s a little function that I found missing from itertools:
def head(iterable, num_items): for obj,i in zip(iterable,xrange(num_items)): yield obj |
UPDATE: Don’t use this head() function, use itertools.islice instead. Thanks go to Erez for pointing that out.
Neat @ first two.
The last one isn’t missing (unless I misunderstood your intent): “enumerate” is a built-in since Python 2.4, I believe.
Yoni: You misunderstood my intent. Head takes the first num_items from iterable.
I’m piggy-backing on zip’s behavior. zip always takes the shorter of the input sequences.
It also works for infinite sequences (such as itertools.count()).
Maybe I should have used itertools.izip instead though, to avoid generating the num_items of iterable at once.
And thanks!
Hi, two suggestions:
1) Replace hex(self)[2:-1] with ‘%x’%self. It’s prettier.
Also, the ‘L’ postfix gets abandoned in Python 3.0 .
2) Your ‘head’ function is just a special case of ‘itertools.islice’ .
1. You are correct. Using %x is more elegant, and will work in Python 3.
2. You are correct on this one as well. In fact, my implementation of head might cause a potential bug. This is because zip (and izip) leave long iterators in an uncertain state, by taking more elements than they should.
Pingback: Aldrin Martoq - Technical Weblog » Blog Archive » The quest for the perfect python enum/constant declaration, Part 2