The document discusses strategies for understanding the CPython implementation of Python without reading the code. It recommends using observation and experimentation techniques like inspecting code behavior, examining commit histories, understanding internal structures through disassembly, running performance tests, and writing tests. Tools mentioned include inspect, timeit, and custom inspection modules. The key message is that these hands-on techniques allow one to critically examine and experiment with the code in ways that provide deeper understanding than just reading it.

1. Exploring*is*Never*Boring

2. @akaptur

3. Exploring*is*Never*Boring
Understanding+CPython+without+
reading+the+code

4. Why$do$this?
!

5. Contribu)ng

6. h"ps://docs.python.org/devguide/

7. "Read&the&code!"

10. Not$reading$the$code

11. Strategies
Observa(on
Experimenta+on

12. Strategy(1:(Observa/on
"Code&is&not&literature&and&we&are&not&readers.&Rather,&
interes4ng&pieces&of&code&are&specimens&and&we&are&
naturalists."
—"Peter"Seibel,"Code"is"not"literature

14. How$to$observe

15. Tools%for%observa,on:%inspect
>>> import random
>>> import inspect
>>> print inspect.getsource(random.choice)
def choice(self, seq):
"""Choose a random element from a non-empty sequence."""
return seq[int(self.random() * len(seq))] # raises IndexError if seq is empty

16. Tools%for%observa,on:%inspect
>>> import random
>>> import inspect
>>> print inspect.getsource(random.choice)
def choice(self, seq):
"""Choose a random element from a non-empty sequence."""
return seq[int(self.random() * len(seq))] # raises IndexError if seq is empty
>>> print inspect.getsource(list.append)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/inspect.py", line 701, in getsource
lines, lnum = getsourcelines(object)
File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/inspect.py", line 690, in getsourcelines
lines, lnum = findsource(object)
File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/inspect.py", line 526, in findsource
file = getfile(object)
File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/inspect.py", line 420, in getfile
'function, traceback, frame, or code object'.format(object))
TypeError: <method 'append' of 'list' objects> is not a module, class, method, function, traceback, frame, or code object
>>> # :(
github.com/punchagan/cinspect

17. Tools%for%observa,on:%history%&%
changelogs

18. Tools%for%observa,on:%history%&%changelogs
hg blame Python/ceval.c
hg log -r ### -p

19. Tools%for%observa,on:%internal%
structure

20. Tools%for%observa,on:%internal%structure
>>> False is False is False

21. Tools%for%observa,on:%internal%structure
>>> (False is False) is False

22. Tools%for%observa,on:%internal%structure
>>> False is False is False
True

23. Tools%for%observa,on:%internal%structure
>>> False is False is False
True
>>> a < b < c
True

24. Tools%for%observa,on:%internal%structure
1 0 LOAD_NAME 0 (False)
3 LOAD_NAME 0 (False)
6 DUP_TOP
7 ROT_THREE
8 COMPARE_OP 8 (is)
11 JUMP_IF_FALSE_OR_POP 23
14 LOAD_NAME 0 (False)
17 COMPARE_OP 8 (is)
20 JUMP_FORWARD 2 (to 25)
>> 23 ROT_TWO
24 POP_TOP
>> 25 POP_TOP
26 LOAD_CONST 0 (None)
29 RETURN_VALUE

25. Tools%for%observa,on:%internal%structure
1 0 LOAD_NAME 0 (a)
3 LOAD_NAME 1 (b)
6 DUP_TOP
7 ROT_THREE
8 COMPARE_OP 0 (<)
11 JUMP_IF_FALSE_OR_POP 23
14 LOAD_NAME 2 (c)
17 COMPARE_OP 0 (<)
20 JUMP_FORWARD 2 (to 25)
>> 23 ROT_TWO
24 POP_TOP
>> 25 POP_TOP
26 LOAD_CONST 0 (None)
29 RETURN_VALUE

26. Strategy(2:(Experimenta1on

28. Tools%for%science:%measurements
e.g.$%meit
$ python -m timeit -s "li = range(100)" "li.sort(reverse=True)"
1000000 loops, best of 3: 1.75 usec per loop
$ python -m timeit -s "li = range(100)" "sorted(li, reverse=True)"
100000 loops, best of 3: 2.46 usec per loop

29. Tools%for%science:%write%tests

30. Tools%for%science:%simula0ons

31. Observa(on+&+Experimenta(on+>+Reading+
the+code
• Introspect+it
• Examine+it+cri1cally
• Watch+it+evolve
• Measure+it
• Test+it
• Change+it
• Poke+it+with+a+s1ck

32. Ques%ons

33. class Random(_random.Random):
"""Random number generator base class used by bound module functions.
Used to instantiate instances of Random to get generators that don't
share state."""
...
# Create one instance, seeded from current time, and export its methods
# as module-level functions. The functions share state across all uses
#(both in the user's code and in the Python libraries), but that's fine
# for most programs and is easier for the casual user than making them
# instantiate their own Random() instance.
_inst = Random()
seed = _inst.seed
random = _inst.random
randint = _inst.randint
choice = _inst.choice
...