`shell invocation` in Python 2

Presentation for Quipper Alumni Meetup held in 2019.

Transcript

1. `shell invocation` in Python 2 @manicmaniac
2. Ryosuke Ito • iOS software engineer • Working for Quipper Ltd. since Apr. 2019 • Loves Python @manicmaniac
3. Python 2
4. EOL of Python 2 2020-01-01 00:00:00 Only 15 days left!
5. Shell invocation
6. In Ruby puts `date`
7. In Perl print `date`
8. In Python 2.7 import subprocess print subprocess.check_output([‘date’]),
9. In Python <= 2.6 import subprocess process = subprocess.Popen(['date'], stdout=subprocess.PIPE), stdout, _ = process.communicate() print stdout,
10. How can I `date`?
11. Backquotes in Python 2 `date` == repr(date) == date.__repr__()
12. Naive implementation import subprocess class date(object): def __repr__(self): return subprocess.check_output(‘date’) date = date() print `date`
13. Using meta class import subprocess def register_command(name): def __repr__(self): return subprocess.check_output( self.__class__.__name__ ) globals()[name] = type( name, (object,), dict(__repr__=__repr__) )() register_command('date') print `date`
14. But how about other commands?
15. import backquotes print `date`
17. How it works?
18. Preprocessing import tokenize def preprocess(filename, readline): for token in tokenize.generate_tokens(readline): ... if inside_backquotes: tokens.extend([ (tokenize.NAME, 'backquotes'), (tokenize.OP, '.'), (tokenize.NAME, 'shell'), (tokenize.OP, '('), ]) ...
19. At Runtime frame = inspect.currentframe().f_back while frame.f_code.co_filename.startswith('<frozen importlib'): frame = frame.f_back execfile(source, frame.f_globals, frame.f_locals)
20. print `date`
21. Limitations • Doesn’t work on REPL • Doesn’t work on Python 3 • Really buggy
22. Backquotes in Python 3 >>> `date` File "<stdin>", line 1 `date` ^ SyntaxError: invalid syntax
23. Don’t use backquotes
24. R.I.P Python 2 Thank you for listening!