Why does shopt fail when called from python?

# shopt -s extglob

# python3
Python 3.4.0 (default, Sep  8 2015, 23:36:36) 
[GCC 4.7.3] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from subprocess import check_call
>>> check_call(['shopt', '-s', 'extglob'])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.4/subprocess.py", line 552, in check_call
    retcode = call(*popenargs, **kwargs)
  File "/usr/lib/python3.4/subprocess.py", line 533, in call
    with Popen(*popenargs, **kwargs) as p:
  File "/usr/lib/python3.4/subprocess.py", line 848, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.4/subprocess.py", line 1446, in _execute_child
    raise child_exception_type(errno_num, err_msg)
FileNotFoundError: [Errno 2] No such file or directory: 'shopt'

shopt doesn't appear to be in my path but bash does:

# echo $PATH | grep shopt
# whereis shopt
# whereis bash
bash: /bin/bash /etc/bash.bashrc /usr/share/man/man1/bash.1.gz

If you want to "rm all but two files in a directory", you can do that directly from Python without invoking a shell. This program removes all of the files in /tmp/r, except for two that I want to keep.

#!/usr/bin/python3

import os

keepers = ['safe', 'also_safe.txt']
os.chdir('/tmp/r')

for filename in os.listdir('.'):
    if filename not in keepers:
        print('Removing %s' % (filename,))
        os.remove(filename)

And, for fun, here is a combined module and script that provide the same functionality:

#!/usr/bin/python3

import os
import argparse
import sys

def safe_remove(dirs, exclude, verbose, dry_run):
    for directory in dirs:
        if verbose or dry_run:
            print("Checking directory '%s'" % (directory,))
        for filename in os.listdir(directory):
            if filename not in exclude:
                filename = os.path.join(directory, filename)
                if verbose or dry_run:
                    print('rm %s'%filename)
                if not dry_run:
                    os.remove(filename)

if __name__ == "__main__":
    parser = argparse.ArgumentParser(description='Remove files, with exceptions')
    parser.add_argument('-x', '--exclude',
                        metavar='FILE',
                        default=[],
                        nargs='+',
                        help='files to exclude')
    parser.add_argument('dirs',
                        metavar='DIR',
                        nargs='+',
                        help='directories to clean')
    parser.add_argument('-v', '--verbose',
                        action='store_true',
                        help='Print actions')
    parser.add_argument('-n', '--dry-run',
                        action='store_true',
                        help='Print, but do not perform, actions')
    args = parser.parse_args()
    safe_remove(**vars(args))