human
Complete the below
def fake_paths_by_regex(pattern, exists=True):

    ''''Usage:
    >>> with fake_paths_by_regex(\'\.pdf$\'):
    ...     assert os.path.exists(\'my.pdf\') == True
    >>> with fake_paths_by_regex(\'\.pdf$\', exists=False):
    ...     assert os.path.exists(\'my.pdf\') == False'
    '''
 ... What is a the Python code you requested?
assistant
#Here is the Python code you requested.
    regex = re.compile(pattern)
    def check(path):
        if regex.search(path):
            return exists
        return None
    return fake_paths(check)