Python 3 provides many improvements over Python 2 including: 1) Improved comparison of different data types, iterators used more widely to reduce memory usage, and keyword-only arguments for cleaner function definitions. 2) Exceptions are now handled more cleanly with exception chaining and specific exception types for I/O errors. 3) Common library names and structures were standardized and new features were added like path handling, caching, subprocess management and async/await syntax. 4) Overall Python 3 rationalizes the language and standard library for modern use cases.

1. 10 Reasons to Adopt Python 3

2. About Me
Pierre Fersing – pierref@bleemeo.com
CTO & co-founder @Bleemeo
Python & Django dev for 10 years

3. Monitoring as a Service solution
API in Django + User Interface in ReactJS

4. ① Comparison in Python
>>> ["user1", 20] < ["user2", 10]
True
>>> ["user1", 20] < ["user1", 30]
True

5. ① Comparison in Python
Py2 : False !
Py3 : TypeError: unorderable types: tuple() < list()
>>> ("user1", 20) < ["user2", 99]
>>> max("one", 2)
"one"

6. ② Iterators, Iterators Everywhere
Consume about 1,5 GB of memory with Python
2 !
range vs xrange, keys vs iterkeys, values vs
itervalues, items vs iteritems
zip, map, filter
>>> for _ in range(50000000):
... the_answer = 42

7. ③ Keywords Only Arguments
>>> def sortwords(
... words, reverse, case_sensitive):
>>> sortwords(
... ["one", "two", "three"],
... reverse=True, case_sensitive=False)

8. ③ Keywords Only Arguments
>>> def sortwords(
... words, reverse, case_sensitive):
>>> sortwords(
... ["one", "two", "three"], True, False)
>>> def sortwords(
... words, case_sensitive, reverse):
>>> def sortwords(
... words, *, case_sensitive, reverse):

9. ③ Keyword Arguments
>>> sortwords(
... "one", "two", "three",
... case_sensitive=False
... )
>>> def sortwords(*words, **kwargs):
... case_sensitive =
... kwargs.pop("case_sensitive")

10. ③ Keyword Arguments
>>> sortwords(
... "one", "two", "three",
... case_sensitive=False
... )
>>> def sortwords(
... *words, case_sensitive=True):

11. ④ Improved Except Syntax
>>> try:
... 0 / 0
... except OSError, ZeroDivisionError:
... print("Error")

12. ④ Improved Except Syntax
>>> try:
... 0 / 0
... except (OSError, ZeroDivisionError) as err:
... print("Error")

13. ⑤ Chained Exceptions
>>> try:
... connection = do_connect()
... # do stuff
... finally:
... connection.close()
Traceback (most recent call last):
File "code.py", line 5, in <module>
connection.close()
NameError: name 'connection' is not defined

14. ⑤ Chained Exceptions
Traceback (most recent call last):
File "plop.py", line 2, in <module>
connection = do_connect()
ConnectionRefusedError: [Errno 111]
Connection refused
During handling of the above exception,
another exception occurred:
Traceback (most recent call last):
File "plop.py", line 5, in <module>
connection.close()
NameError: name 'connection' is not defined

15. ⑥ Reworked OS/IO Exception
>>> try:
... fd = open("/etc/shadow")
... except IOError:
... print("Error")
>>> try:
... os.stat("/etc/shadow")
... except OSError:
... print("Error")

16. ⑥ Reworked OS/IO Exception
>>> try:
... fd = open("/etc/shadow")
... except IOError as err:
... if err.errno in (EACCES, EPERM):
... print("Error")
... else:
... raise

17. ⑥ Reworked OS/IO Exception
>>> try:
... fd = open("/etc/shadow")
... except PermissionError:
... print("Error")

18. ⑦ Reworked Stdlib Names
Which module ? urllib, urllib2, urlparse ?
– Parsing an url : urlparse
– Quoting an URL : urllib
– Do a requests : urllib2
No more cPickle, cProfile, cStringIO

19. ⑧ Stdlib Additions
>>> etc = pathlib.Path("/etc")
... file = etc / "passwd"
... file.read_text()
>>> @functools.lru_cache(max_size=32)
... def expansive_function(params):

20. ⑧ Stdlib Additions
>>> subprocess.run(
... ["ls", "-l"], timeout=10)
>>> datetime.now().timestamp()
>>> secrets.token_urlsafe()

21. ⑧ Stdlib Additions
Lots more :
– lzma
– enum
– ipaddress
– faulthandler
– statistics
– ...

22. ⑨ asyncio and async/await
>>> reader,writer = await asyncio.open_connection(
... "www.python.org", 80)
... writer.write(b'GET / […]')
... async for line in reader:
... # do something with the line

23. ⑩ Bonus
>>> 1 / 2
0.5
>>> for x in iterable:
... yield x
>>> yield from iterable

24. ⑩ Bonus
Tab-completion in interpreter
>>> class Children(Parent):
... def method(self):
... super().method()

25. ⑩ Bonus
>>> round(1.5)
2
>>> round(2.5)
2

26. Question ?