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What does set mean in python

藏色散人

Jun 24, 2019 am 10:10 AM

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What does set mean in python?

set is a set of numbers, unordered, and the content cannot be Repeat, created by calling the set() method:

>>> s = set([&#39;A&#39;, &#39;B&#39;, &#39;C&#39;])

The meaning of accessing a set is only to check whether an element is in the set. Pay attention to case sensitivity:

>>> print &#39;A&#39; in s
True
>>> print &#39;D&#39; in s
False

also passes for to traverse:

s = set([(&#39;Adam&#39;, 95), (&#39;Lisa&#39;, 85), (&#39;Bart&#39;, 59)])
for x in s:
    print x[0],&#39;:&#39;,x[1]
>>>
Lisa : 85
Adam : 95
Bart : 59

Add and delete elements through add and remove (keep them non-repeating). When adding elements, use the add() method of set

>>> s = set([1, 2, 3])
>>> s.add(4)
>>> print s
set([1, 2, 3, 4])

If the added element already exists In set, add() will not report an error, but it will not be added:

>>> s = set([1, 2, 3])
>>> s.add(3)
>>> print s
set([1, 2, 3])

When deleting elements in set, use the remove() method of set:

>>> s = set([1, 2, 3, 4])
>>> s.remove(4)
>>> print s
set([1, 2, 3])

If deleted If the element does not exist in the set, remove() will report an error:

>>> s = set([1, 2, 3])
>>> s.remove(4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 4

So if we want to determine whether an element meets some different conditions, using set is the best choice. The following example:

months = set([&#39;Jan&#39;,&#39;Feb&#39;,&#39;Mar&#39;,&#39;Apr&#39;,&#39;May&#39;,&#39;Jun&#39;,&#39;Jul&#39;,&#39;Aug&#39;,&#39;Sep&#39;,&#39;Oct&#39;,&#39;Nov&#39;,&#39;Dec&#39;,])
x1 = &#39;Feb&#39;
x2 = &#39;Sun&#39;
if x1 in months:
    print &#39;x1: ok&#39;
else:
    print &#39;x1: error&#39;
if x2 in months:
    print &#39;x2: ok&#39;
else:
    print &#39;x2: error&#39;
>>>
x1: ok
x2: error

In addition, the calculation efficiency of set is higher than that of list.

Related recommendations: "Python Tutorial"

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