In Python is augmented addition of sets are not supported?

In the Python开发者_StackOverflow社区 sets, why augmented removal of elements are supported but addition is not supported?

For example if s is a mutable set:

s = set(['e', 'd', 'h', 's'])

s -= set('ds') gives s = set(['e', 'h'])

but this does not work for s += set('pk') and results in TypeError.

The correct syntax for what you want to do is

s |= set('ds')

For sets, the binary operators |, & and ^ are used for union, intersection and symmetric difference, respectively. I guess the reason + is not considered a valid set operation is because it is not used in set theory, while - is.

There's a nice symmetry between the way these three binary operators work on integers and the way they work on sets:

set("1234")  & set("1456") == set(['1', '4'])
bin(0b111100 & 0b100111)   == '0b100100'
#     1234       1  456          1  4

set("14")    | set("456")  == set(['1', '5', '4', '6'])
bin(0b100100 | 0b000111)   == '0b100111'
#     1  4          456          1  456

set("14")    ^ set("456")  == set(['1', '5', '6'])
bin(0b100100 ^ 0b000111)   == '0b100011'
#     1  4          456          1   56

You could use s | set('ds'), assuming s = set('edhs')

First of all python tutorial is your the very best friend and contains all information you need. You can take a look at the following link to get more info about python set types: http://docs.python.org/release/2.7/library/stdtypes.html?highlight=set.difference#set-types-set-frozenset

You can use set union method for this purpose:

union(other, ...) is the same as set | other | ...

Return a new set with elements from the set and all others.

baseSet = set('abcd')
baseSet = baseSet.union('zx')

Or using set update method:

update(other, ...) is the same as set |= other | ...

Update the set, adding elements from all others.

baseSet = set('abcd')
baseSet.update('zx')