# General utility functions can go here.

import os

import random

import string

from django.utils import functional

from django.utils.http import urlencode

def rand_string(numOfChars):

"""

Generates a string of lowercase letters and numbers.

That makes 36^10 = 3 x 10^15 possibilities.

If we generate filenames randomly, it's harder for people to guess filenames

and type in their URLs directly to bypass permissions.

"""

return ''.join(random.choice(string.ascii_lowercase + string.digits) for i in range(numOfChars))

def generate_random_filename(directory, originalFilename, numOfChars):

"""

Generate a random filename for a file upload. The filename will

have numOfChars random characters. Also prepends the directory

argument to get a filepath which is only missing the MEDIA_ROOT

part at the beginning.

The return value can be used as an upload_to argument for a FileField

ImageField, ThumbnailerImageField, etc. An upload_to argument is

automatically prepended with MEDIA_ROOT to get the upload filepath.

"""

# TODO: Use the directory argument to check for filename collisions with existing files.

# To unit test this, use a Mocker or similar on the filename randomizer

# to make filename collisions far more likely.

extension = os.path.splitext(originalFilename)[1]

filenameBase = rand_string(numOfChars)

return os.path.join(directory, filenameBase + extension)

def url_with_querystring(path, **kwargs):

"""

Takes a base URL (path) and GET query arguments (kwargs).

Returns the complete GET URL.

NOTE:

Any kwargs with special characters like '/' and ' ' will be

escaped with %2f, %20, etc.

Source:

http://stackoverflow.com/a/5341769/859858

"""

return path + '?' + urlencode(kwargs)

def is_django_str(s):

"""

Checks that the argument is either:

(a) an instance of basestring, or

(b) a Django lazy-translation string.

:param s: Object to check the type of.

:return: True if s is a Django string, False otherwise.

"""

if isinstance(s, basestring):

return True

elif isinstance(s, functional.Promise):

return True

else:

return False