`shell invocation` in Python 2 @manicmaniac 

Ryosuke Ito • iOS software engineer • Working for Quipper Ltd. since Apr. 2019 • Loves Python @manicmaniac 

Python 2 

EOL of Python 2 2020-01-01 00:00:00 Only 15 days left! 

Shell invocation 

In Ruby puts `date` 

In Perl print `date` 

In Python 2.7 import subprocess print subprocess.check_output([‘date’]), 

In Python <= 2.6 import subprocess process = subprocess.Popen(['date'], stdout=subprocess.PIPE), stdout, _ = process.communicate() print stdout, 

How can I `date`? 

Backquotes in Python 2 `date` == repr(date) == date.__repr__() 

Naive implementation import subprocess class date(object): def __repr__(self): return subprocess.check_output(‘date’) date = date() print `date` 

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` 

But how about other commands? 

import backquotes print `date` 

No content

How it works? 

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, '('), ]) ... 

At Runtime frame = inspect.currentframe().f_back while frame.f_code.co_filename.startswith('

print `date` 

Limitations • Doesn’t work on REPL • Doesn’t work on Python 3 • Really buggy 

Backquotes in Python 3 >>> `date` File "", line 1 `date` ^ SyntaxError: invalid syntax 

Don’t use backquotes 

R.I.P Python 2 Thank you for listening!