Replace for-append with generator

# New smell

### Smelly code
```py
li = list()
for x in other_iterable:
    # Body
    li += expr
```
### Fixed code
```py
def generate_li():
    # Body
    yield expr
li = list(generate_li())
```
### Why is it smelly?
Not as smelly:tm: as other things, but in some cases it makes more sense, and more people should be aware of the possibility.