Python convert set to string and vice versa

Question

Set to string. Obvious:

>>> s = set([1,2,3])
>>> s
set([1, 2, 3])
>>> str(s)
'set([1, 2, 3])'

String to set? Maybe like this?

>>> set(map(int,str(s).split('set([')[-1].split('])')[0].split(',')))
set([1, 2, 3])

Extremely ugly. Is there better way to serialize/deserialize sets?

Answer 1

Try like this,

>>> s = set([1,2,3])
>>> s = list(s)
>>> s
[1, 2, 3]

>>> str = ', '.join(str(e) for e in s)
>>> str = 'set(%s)' % str
>>> str
'set(1, 2, 3)'

Answer 2

Use repr and eval:

>>> s = set([1,2,3])
>>> strs = repr(s)
>>> strs
'set([1, 2, 3])'
>>> eval(strs)
set([1, 2, 3])

Note that eval is not safe if the source of string is unknown, prefer ast.literal_eval for safer conversion:

>>> from ast import literal_eval
>>> s = set([10, 20, 30])
>>> lis = str(list(s))
>>> set(literal_eval(lis))
set([10, 20, 30])

help on repr:

repr(object) -> string
Return the canonical string representation of the object.
For most object types, eval(repr(object)) == object.

Answer 3

If you do not need the serialized text to be human readable, you can use pickle.

import pickle

s = set([1,2,3])

serialized_s = pickle.dumps(s)
print "serialized:"
print serialized_s

deserialized_s = pickle.loads(serialized_s)
print "deserialized:"
print deserialized_s

Result:

serialized:
c__builtin__
set
p0
((lp1
I1
aI2
aI3
atp2
Rp3
.
deserialized:
set([1, 2, 3])