What is the difference between a generator and a list comprehension?

[Pedroski55]

I'm new to generators. Reuven Lerner describes them as "lazy lists"

This one assigns the letters of a string to alist a prescribed number of times.

But alist has no values.

Is this because the generator only makes the values when called by print(list(alist))??

What exactly is alist here? Is it like a function that can be called?

#! /usr/bin/python3
# simple generator

myString = 'generator'
n = len(myString)
max_times = 12
alist = (myString[x % n] for x in range(max_times))

# alist returns <generator object <genexpr> at 0x7fb489ca4ba0> in Idle
# print(alist) returns <generator object <genexpr> at 0x7fb489ca4ba0> in Idle

print(list(alist)) # returns ['g', 'e', 'n', 'e', 'r', 'a', 't', 'o', 'r', 'g', 'e', 'n']

If I use a list comprehension, I get a list:

alist2 = [myString[x%n] for x in range(max_times)]

Enter alist2 in Idle and I immediately get:

>>> alist2
['g', 'e', 'n', 'e', 'r', 'a', 't', 'o', 'r', 'g', 'e', 'n']
>>>

What is the difference between a generator and a list comprehension??

Maybe, the generator uses less memory, only works on demand??