Demo: work with filesystem in Python

gistfile1.py

#!/usr/bin/python
# -*- coding: utf-8 -*-

# First line is for OS to know which interpreter to use when executing this file. You can easily determine where is your Python installation
# by typing `$ which python` into your bash terminal. You can of course run Python scripts this way: `$ python myscript.py`.

# Second line tells interpreter (and most editors, e.g. vim) that your file is in UTF-8. Any non-ASCII characters here, such as áéíóů
# will be treated as UTF-8 by Python interpreter thanks to this. See PEP 0263 for further info: http://www.python.org/dev/peps/pep-0263/


import os
import getpass
import glob
import re


# Let's try some IO operations. Further reading is here: http://docs.python.org/tutorial/inputoutput.html#reading-and-writing-files


try:
    with open('/tmp/gargamel', 'w') as f:
        f.write('I hate smurfs!')

except IOError:
    print 'Gargamel says: Ouch!'


# What about reading?


try:
    with open('/tmp/gargamel', 'r') as f:
        print 'Gargamel says: %s' % f.read()

except IOError:
    print 'Gargamel says: Ouch!'
    

# Okay. I'll omit the try/except blocks for now, you probably got the point of catching exceptions.
# Let's play a bit with http://docs.python.org/library/os.html.


print 'There are %d items in your temp directory.' % len(os.listdir('/tmp'))


# Tip: One great source of wisdom is here http://diveintopython.org/file_handling/os_module.html.


user = getpass.getuser()
print 'Your home directory contains: %s' % ', '.join(filter(lambda x: not x.startswith('.'), os.listdir('/home/%s/' % user)))


# Well, that was a bit more "declarative". We determined current OS user's name, then listed his/her own home directory.
# Because we don't want any junk in our listing, we filtered out files which start with dot. Then we got a list of directory items.
# We glued it together with ', ' strings and printed out.


# Now let's start with something useful. First make some place for it:


print '\n\n'


# The goal: find mkv files. If there is mp4 file in the same directory and with the same name, set "date modified" to mkv to the same
# value as mp4 has. Mind diacritics, Windows box specifics, special characters.


def find(dir, condition):
    """Recursivly walks through a directory. Generates filenames which satisfy condition."""
    dir = os.path.abspath(dir)
    for f in os.listdir(unicode(dir)):
        f_path = os.path.join(dir, f)
        if os.path.isdir(f_path):
            for f_sub in find(f_path, condition):
                yield f_sub
        elif condition(f_path):
            yield f_path


def mkv_to_mp4(mkv_file):
    """Returns name of twin mp4 file to given mkv file."""
    return re.sub(r'\.mkv$', '.mp4', mkv_file)


def cond(file):
    """Condition for searching: only mkv files, which have twin mp4 file."""
    return re.search(r'\.mkv$', file) and os.path.isfile(mkv_to_mp4(file))


# Now the final (not properly tested!) piece of code. Using docs.python.org/library/os.html


for mkv_file in find('/tmp/python-script-test/', cond): # on Windows box: 'D:\\tmp\\python-script-test\\'
    mp4_file = mkv_to_mp4(mkv_file) # get name of twin mp4 file
    stat = os.stat(mp4_file) # get stat of twin mp4 file
    os.utime(mkv_file, (stat.st_atime, stat.st_mtime)) # save times to mkv files


# Maybe there is even easier way :) . And trust me, there usually is something easier...
# and also more "pythonish", more declarative, more dependent on Python protocols... :) The language always suprises me.