1. replacing
import with
accio in
CPython

2. >>> import sys!
>>> accio sys!
SyntaxError

3. >>> import sys!
>>> accio sys!
SyntaxError

4. >>> import sys!
>>> accio sys!
SyntaxError

5. >>> accio sys!
>>> import sys!
SyntaxError

6. >>> accio sys!
>>> import sys!
SyntaxError

7. >>> accio sys!
>>> import sys!
SyntaxError

8. why?

9. we’ll learn:!
what is a
statement

10. we’ll learn:!
what is a
SyntaxError

11. we’ll learn:!
how does
Python know
the difference?

12. we’ll learn:!
bootstrapping
!

13. replacing
import with
accio

14. import is a
statement

15. statements
are defined in
the Grammar!
file

16. import_stmt: !
import_name | !
import_from

17. import_name: !
‘import’ !
dotted_as_names

18. first attempt

19. import_name: !
‘accio’ !
dotted_as_names

20. $ make

21. import sys!
^!
SyntaxError:
invalid syntax

22. oops

23. second
attempt

24. $ sed ’s/
import/accio’

25. $ make

26. accio sys!
^!
SyntaxError:
invalid syntax

27. bootstrapping
!

28. third attempt

29. import_name: !
‘import’ !
dotted_as_names!
| ‘accio’ !
dotted_as_names

30. $ make

31. $PATH

32. import_name: !
‘accio’ !
dotted_as_names

33. $ sed ’s/
import/accio’

34. $ make

35. >>> accio sys!
>>> import sys!
SyntaxError

36. >>> accio sys!
>>> import sys!
SyntaxError

37. >>> accio sys!
>>> import sys!
SyntaxError!

38. links
• Grammar - https://docs.python.org/2/reference/
grammar.html
• EBNF - http://en.wikipedia.org/wiki/
Extended_Backus%E2%80%93Naur_Form
• Adding a statement - http://
eli.thegreenplace.net/2010/06/30/python-
internals-adding-a-new-statement-to-python/

39. @amygdalama!
mathamy.com