Re-learning Python - Alex Martelli

51 Pages·2004·0.22 MB·English

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Re-learning Python
• Alex Martelli
STRAKT
© 2004 AB STRAKT
1
This talk & its audience
you know, or used to know, s/thing about

Python 1.5.2 (or other Python < 2.2)
you're experienced programmers in some

other language[s] (I'm covering in 1h
about 2 days' worth of "normal" tutorials)
you'd like to understand whether it's

worth your while to re-learn Python
today, and what are the highlights
STRAKT
© 2004 AB STRAKT 2
Python’s Progress
Ver. released new for (months)
1.5.2 1999/04 17
stable
2.0 2000/09 07
s/what stable
2.1 2001/04 08
s/what stable
2.2 2001/12 19
stable
2.3 2003/07 (15?)
very stable
(2.4 2004/10?)
STRAKT
© 2004 AB STRAKT 3
Five years’ worth of goodies
Unicode and codecs

list comprehensions

iterators and generators

new classes, metaclasses, descriptors

nested scopes

...“and a cast of thousands”...

+ lots of library additions/enhancements

STRAKT
© 2004 AB STRAKT 4
Python Versions’ Stability
revolutions 1.5.2→2.0→2.1→2.2

stability 2.2→2.3

• only very minor language changes
• overall, ~3 years’ worth of stable experience
• focus on implementation speed, size, solidity
• (library does keep growing & getting better)
...net result...:

Never been readier for prime time!
STRAKT
© 2004 AB STRAKT 5
Unicode and codecs
unicode strings vs plain byte strings

• methods make them polymorphic
encode/decode for string transforms

(including to/from Unicode/plain)
print 'ciao'.decode('rot13')
pnvb
STRAKT
© 2004 AB STRAKT 6
List comprehensions
L = [ x*x for x in LL if x>0 ]
{x*x | x(cid:15464)L, x>0} --
like, in set theory is just like...:
,
L = []
for x in LL:
if x>0:
L.append(x*x)
pluses: 1 thought → 1 compact idiom
it's an expression...
STRAKT
© 2004 AB STRAKT 7
Iterators: in 1.5.2 ...
To allow looping with a for, one had to
sort-of-emulate a sequence...:
class iterable:
def __getitem__(self, i):
if self.done():
raise IndexError
return self.next()
+ safeguards vs random-access, restart...
STRAKT
© 2004 AB STRAKT 8
Iterators: since 2.2 ...
A class is iterable if it has a special method
__iter__ returning an iterator object:
class iterable:
def __iter__(self):
return my_iter(self)
Each instance of the iterator class keeps
track of one iteration's state, returns self
from __iter__, has a method next
STRAKT
© 2004 AB STRAKT 9
Iterators: an iterator class
class myiter:
def __init__(self, ...):...
def __iter__(self):return self
def next(self):
[[...advance one step...]]
if [[it's finished]]:
raise StopIteration
return [[the next value]]
STRAKT
© 2004 AB STRAKT 10