How to create a file in python if it does not exists

You can check if all directories in file_path exist prior to trying to write a file.

import os

file_path = '/Users/Foo/Desktop/bar.txt' 
print os.path.dirname(file_path)  
# /Users/Foo/Desktop

if not os.path.exists(os.path.dirname(file_path)):
    os.mkdirs(os.path.dirname(file_path))  
    # recursively create directories if necessary

with open(file_path, "a") as my_file:
    # mode a will either create the file if it does not exist
    # or append the content to its end if it exists.
    my_file.write(your_text_to_append)

-- Edit: Small and probably unnecessary extension --

expanduser:
In your case, as it turned out that the initial problem was a missing s in the path to the user directory, there is a useful feature for resolving the current users base directory (works for unix, linux and windows): see expanduser from the os.path module. With that you could write your path as path = '~/Desktop/bar.txt' and the tilde (~) will be expanded just like on your shell. (with the additional benefit that if you started your script from another user it would then expand to her home directory.

App config directory:
Since in most cases it is not desirable to write a file to the desktop (*nix systems for instance might not have a desktop installed), there is a great utility function in the click package. If you look at the get_app_dir() function on Github, you can see how they provide expanding to an appropriate app dir and supporting multiple operating systems (the function has no dependencies besides the WIN variable that is defined in the _compat.py module as WIN = sys.platform.startswith('win') and the _posixify() function defined on line 17. Often that's a good starting point for defining an app directory to store certain data in.

It shall be as simple as:

fname = "/User/rokumar/Desktop/sample.csv"
with open(fname, "a") as f:
    # do here what you want
# it will get closed at this point by context manager

But I would suspect, that you are trying to use not existing directory. Usually, "a" mode creates the file if it can be created.

Make sure, the directory exists.

import os

def get_rum_data(file_path, query):
    if file_path is not None and query is not None:

        if not os.path.exists(os.path.dirname(file_path)) and os.path.dirname(file_path) not in [None, '', ' ']:
            os.makedirs(os.path.dirname(file_path))
        if not os.path.isfile(file_path):
            with open(file_path, 'x') as fp:
                pass

        command = FETCH_RUM_COMMAND_DATA % (constants.RUM_JAR_PATH, 
                                            constants.RUM_SERVER, file_path, 
                                            query)
        print command
        execute_command(command).communicate()

Bibliography:

• https://docs.python.org/3/library/functions.html#open
• https://docs.python.org/3/library/os.path.html#module-os.path

Just creating an empty file if it doesn't exist:

if not os.path.isfile(file_path):
    with open(file_path, 'x') as fp:
        pass

Creating the file's full absolute path recursively if any directory or subdirectory doesn't exist:

if not os.path.exists(os.path.dirname(file_path)) and os.path.dirname(file_path) not in [None, '', ' ']:
    os.makedirs(os.path.dirname(file_path))

If you don't include the test for empty dirnames (which is the case when file_path is 'example.txt' instead of '/path/to/example.txt', it will raise an exception.