As of 1999, there were two documented attacks by green anacondas (Eunectes murinus) on humans. Neither human was eaten, see Predatory attacks of green anacondas (Eunectes murinus) on adult human beings, Herptological Natural History. 6(2): 158-160:
In my experience catching anacondas of all sizes, I have found that
large individuals are very unlikely to attack when disturbed. Indeed,
to the present I have caught and processed more than 120 animals
larger than 4 meters and none tried to bite until I (or one of my
helpers) had either, dragged the animal out of the water by its tail,
or secured a firm grip on the animal’s neck (Rivas 1999). Large
individuals tended to swim away when disturbed. Recaptured animals
are, if anything, even more skittish than naive ones and try to escape
as soon as they detect the proximity of the researchers.
Note the concluding sentence though,
Although anacondas are not "man-eaters" by nature, they are
generalists and will take any prey that they can subdue and swallow.
Thus, the potential exists for anacondas to prey on people.
Another credible source explains why human consumption by anaconda is unlikely and remains undocumented as of 2012 see section six, Did they ever try and eat you?
Pythons and especially reticulated pythons are a different matter; a 10 year-old was swallowed in 2002 in South Africa, and in the 1970’s a Portugese soldier was found inside the stomach of a python.