So clearly there cannot be unlimited memory in Python. I am writing a script that creates lists of dictionaries. But each list has between 250K and 6M objects (there are 6 lists).

Is there a way to actually calculate (possibly based on the RAM of the machine) the maximum memory and the memory required to run the script?

The actual issue I came across:

In running one of the scripts that populates a list with 1.25-1.5 million dictionaries, when it hits 1.227... it simply stops, but returns no error let alone MemoryError. So I am not even sure if this is a memory limit. I have print statements so I can watch what is going on, and it seems to buffer forever as nothing is printing and up until that specific section, the code is running a couple thousand lines per second. Any ideas as to what is making it stop? Is this memory or something else?

If you have that many objects you need to store, you need store them on disk, not in memory. Consider using a database.

If you import the sys module you will have access to the function sys.getsizeof(). You will have to look at each object of the list and for each dictionary compute the value for every key. For more on this see this previous question - In-memory size of a Python structure.