[docs] Import error macOS

[Brent Leeper]

Hello,

I have been using python3 for several years but have never seen this error.

Description:
After executing “python3” and starting the cli, I can import the following without error
-from cassandra.cluster import Cluster
Then I exit and run a .py file whose first line is “from cassandra.cluster import Cluster” which results in the following error.
-Traceback (most recent call last):
  File "cassandra.py", line 1, in <module>
    from cassandra.cluster import Cluster
  File "/Users/<user>/Documents/learning/cassandra.py", line 1, in <module>
    from cassandra.cluster import Cluster
ModuleNotFoundError: No module named 'cassandra.cluster'; 'cassandra' is not a package

Sure, the import did not work. But the next part is the issue. 

Now I return back to the cli by executing “python3” and I enter the following (the same as above”)
-from cassandra.cluster import Cluster

Now I get this error:
-Python 3.7.4 (v3.7.4:e09359112e, Jul  8 2019, 14:54:52) 
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from cassandra.cluster import Cluster
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/<user>/Documents/learning/cassandra.py", line 1, in <module>
    from cassandra.cluster import Cluster
ModuleNotFoundError: No module named 'cassandra.cluster'; 'cassandra' is not a package

The error is referencing the file but I am not executing it. This is very odd. 
This continues until I close the terminal instance and open a new one and is reproducible if you take the above steps on my system.

If you would like further details, please let me know.


Thanks,
Brent