what is the difference and uses of these lines of code?

first line of code:

for i in list:
   print(i)

second line of code:

print(i for i in list)

what would I use each of them for?

Answer

You can see for yourself what the difference is. The first one iterates over range and then prints integers.

>>> for i in range(4):
...     print(i)
...
0
1
2
3

The second one is a generator expression.

>>> print(i for i in range(4))
<generator object <genexpr> at 0x10b6c20f0>

How iteration works in the generator. Python generators are a simple way of creating iterators.

Simply speaking, a generator is a function that returns an object (iterator) which we can iterate over (one value at a time).

>>> g=(i for i in range(4))
>>> print(g)
<generator object <genexpr> at 0x100f015d0>
>>> print(next(g))
0
>>>
>>> print(next(g))
1
>>> print(next(g))
2
>>> print(next(g))
3
>>> print(next(g))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration


>>> g=(i for i in range(4))
>>> for i in g:
...     print(i)
...
0
1
2
3
>>> for i in g:
...     print(i)
...
>>>
>>>

In python3, you can use tuple unpacking to print the generator. If that’s what you were going for.

>>> print(*(i for i in range(4)))
0 1 2 3