Switch to Python 3…now…immediately

Switch to Python 3…
Now…
Immediately!

Prof Russel Winder
http://www.russel.org.uk

email: russel@winder.org.uk
xmpp: russel@winder.org.uk
twitter: @russel_winder

Copyright © 2013 Russel Winder 1

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polemic
noun
a strong verbal or written attack on someone or something


Introduction


2.6 2.7
2.5
2.4
2.3
2.2


3.3
3.2
3.1
3.0

gs/2../3.3/g


So what's the problem?
● Python 2 remains the default Python.
● Too many people and organizations are far too
afraid of change.

Why do people and organizations
become so afraid of change?


So what's the solution?
● Python Software Foundation (PSF) should declare
Python 3 the default Python immediately.

People and organizations can implement this now:
python → python2
replaced by:
python → python3


But…world, we have a problem…
● …a few influential organizations are telling people
not to use Python 3 but to stay with Python 2,
and… 
Afraid of change?

● …some crucial projects can't or won't get Python 3
versions out. 
Afraid of change?

Many projects are now both Python 2 and
 Python 3 or getting there very rapidly.

Recalcitrant organizations and projects

should just pull their fingers out and

set Python 3 as their standard.


Or at least ensure their codebases

run under both Python 2 and Python 3.


Being Python 2 and 3 compatible
● 2to3 not useful, its a one shot transform tool.
● six package might be useful in parts, and/or…
● …modernize package might help, but…
● …is manual the best?


Embrace

managed and controlled

change.


Be agile.


Justifications


Python 2 is a dead end.

Python 3 is the developing future.


print(x)

exec(x)


from __future__ import print_function


from __future__ import (
division,
absolute_import,
print_function,
unicode_literals,
)


x = [x * x for x in range(100) if x % 10 == 0]


x = {x * x for x in range(100) if x % 10 == 0}


x = {x: x * x for x in range(100) if x % 10 == 0}


Sadly (!) Python 2.7 is getting

backports of things from Python 3.


Fortunately Python 2.6

and earlier are not.


Python 2 is strict,

Python 3 is (sort of) lazy


map(lambda x: x * x,
filter(lambda x: x % 10 == 0, range(100))


range(x) tuple(range(x))

→
xrange(x) range(x)


Not Sequences, but Iterators
items
keys
values
iteritems
→ items
iterkeys keys
itervalues values


Competition


Python is under challenge
● Go is taking over from Python for many people.
● Native, not interpreted.
● Solid concurrency model – CSP
● D is hoping to take over from C, C++, Go, Python.
● Native, not interpreted.
● Solid concurrency models – actors, data parallelism


Native code languages are now

as expressive as Python.


And native code programs are

way, way faster than Python programs.


Statically compiled languages catch errors at

compile time that are horrendous run

time bugs in dynamic languages.


Are you concurrent?
● Who's using thread?
● Who's using threading?


Are you parallel?
● Who's using thread?
● Who's using threading?
● Who's using multiprocessing?


At least IronPython and Jython

do not have a GIL as

CPython and PyPy do.


Support the PyPy STM/AME experiment.


Dataflow
Operators connected by
Actors channels with activity
Independent processes triggered by arrival of
communicating via data on the channels.
asynchronous exchange
of messages

CSP
Sequential processes
connected by channels
using synchronous message
exchange (rendezvous).

Actors
Independent processes
communicating via
asynchronous exchange
of messages


Dataflow
Operators connected by
channels with activity
triggered by arrival of
data on the channels.


CSP
Sequential processes
connected by channels
using synchronous message
exchange (rendezvous).

Data Parallelism
Transform a sequence to
another sequence where all
individual actions happen
at the same time.


Futures are the future.


Along with process pools

and thread pools.


Concurrent.futures
● Python 3.2 package to abstract over threads and
processes to give an asynchronous function call and
future system.

cf. futures package for Python 2.


Talking of PyPy…


Support PyPy for Python 3.


Conclusion


There are no real reasons

to stay with Python 2…


…so Python 3 should be

Considered mandatory.


Challenge


Problem

Python 3
Python 2

Is there a problem, the solution to which can
be coded in Python 2, but not better in Python 3?


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Switch to Python 3…
Now…
Immediately!

Prof Russel Winder
http://www.russel.org.uk

email: russel@winder.org.uk
xmpp: russel@winder.org.uk
twitter: @russel_winder


Switch to Python 3…now…immediately

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Switch to Python 3…now…immediately