Python 3 reference · Set Methods

Python Set add() Method

Add one element to the set. Adding an element that is already present does nothing.

Syntax

set.add(elem)

Parameter	Description
`elem`	A hashable value.

None.

Add elementsTry it yourself

seen = {"a"}
seen.add("b")
seen.add("a")
print(sorted(seen))

Output

['a', 'b']

Track what you've seenTry it yourself

visited = set()
for page in ["home", "about", "home"]:
    if page in visited:
        print("already saw", page)
    visited.add(page)

Output

already saw home

Version	Change
Python 3.0	Added

set.update() · Add all elements from one or more iterables to the set, in place. The same as a |= b.
set.discard() · Remove an element if it is present; do nothing if it isn't. The no-error version of remove().
set.remove() · Remove an element from the set. Raises KeyError if it isn't present; use discard() to avoid the error.
Python Sets · tutorial