# Set TypesΒΆ

A set object is an unordered collection of distinct hashable objects. Common
uses include membership testing, removing duplicates from a sequence, and
computing mathematical operations such as intersection, union, difference, and
symmetric difference. There are two built-in types in Python: `set`

and
`frozenset`

. *However, both types are not supported in RPython*.

Attention

sets are not directly supported in RPython. Instead you should use a plain dict and fill the values with None. Values in that dict will not consume space.

Right now, we can use dict to simulate a set.

```
def sets():
# Since set is not supported in RPython, we use dict with None as values to
# simulate a set.
s1 = {'foo': None, 'bar': None, 'baz': None, 'foo': None, 'baz': None}
if 'fooo' not in s1: print 'fooo is not in the set s1'
if 'foo' in s1: print 'foo is in the set s1'
for i in s1: print i
s2 = {'foo': None, 'hello': None, 'world': None, 'foo': None}
# union
def set_union(s1, s2):
s3 = s1.copy()
s3.update(s2)
return s3
print 'union:'
s3 = set_union(s1, s2)
for i in s3: print i
# intersection:
def set_intersection(s1, s2):
s3 = {}
for i in s1:
if i in s2:
s3.update({i: None})
for i in s2:
if i in s1:
s3.update({i: None})
return s3
print 'intersection:'
s3 = set_intersection(s1, s2)
for i in s3: print i
def entry_point(argv):
sets()
return 0
def target(*args): return entry_point
if __name__ == "__main__":
import sys
entry_point(sys.argv)
```

All set operations and methods in the following code are *not supported* in
RPython.

```
################### UNSUPPORTED IN RPYTHON ######################
def sets_unsupported():
s1 = set(['foo', 'bar', 'baz', 'foo'])
s2 = set(['foo', 'hello', 'world', 'foo'])
if 'fooo' not in s1: print 'fooo is not in the set s1'
if 'foo' in s1: print 'foo is in the set s1'
print s1
# union
print s1.union(s2)
print s1 | s2
# intersection
print s1.intersection(s2)
print s1 & s2
# difference
print s1.difference(s2)
print s1 - s2
# symmetric difference
print s1.symmetric_difference(s2)
print s1 ^ s2
# whether or not two sets have any elements in common
print s1.isdisjoint(s2)
# whether one set is a subset/superset of the other
print s1.issubset(s2)
print s1 <= s2
print s1.issubset(s2)
print s1 >= s2
# whether on set is a proper subset/superset of the other
print s1 < s2
print s1 > s2
# modifying a set
s1 |= s2
s1.update(['fob', 'bah'])
s1.add('boz')
s1.remove('boz')
s1.pop()
s2.clear()
print s1
fs = frozenset(['foo', 'bar', 'baz']) # frozenset is immutable
print fs
def entry_point(argv):
sets_unsupported()
return 0
def target(*args): return entry_point
if __name__ == "__main__":
import sys
entry_point(sys.argv)
```