len("automatically")
len([1,1,5,1,4])
len(("one",))
识别字符串长度
x=[1,2,3,4,5] x.append(6) x #如下功能相同 x=[1,2,3,4,5] list.append(x,6) x
向数组中加入新的对象
. 用于存取对象的某个属性
x=[1,2,3,4,5] x[0]
索引从0开始，这里会输出1
x=[1,2,3,4,5] x[2]=7
3会变成7
>>> a=["wow",23] >>> b=["wow",23] >>> a is b False >>> b=a >>> a is b True
当is左右的对象指向的是同一个对象，会返回true
>>> a=3 >>> b=3 >>> a is b True >>> a==b True >>> a=banana >>> b=banana >>> a is b True >>> a==b True >>> a="faker" >>> b="faker" >>> a is b True >>> a==b True
当给对象赋的是单一数值而非数组时，非同一对象用is判定是true
>>> c="absolutely" >>> d= None >>> c is not None,d is None (True, True)
反向测试。None用作位置标记值，指示“未知”或“不存在”
>>> a=3 >>> b=5 >>> a==b False >>> a>> a<=b,a!=b (True, True)
==表示等于，!=表示不等于，<=小于等于，>=大于等于
>>> a=["more",5] >>> b=["more",5] >>> a==b True
a与b是不同的对象，但有相同的值，所以比较结果是True
>>> a=55 >>> 0<=a<=56 True
链式结构
>>> x=["absolutely",2,3] >>> 2 in x True >>> "ab" not in x True >>> "fake" in x False
in用来判定对象是否在数组中
>>> absolutely="fake a smile" >>> "k" in absolutely True >>> "mil" in absolutely True
查找字符是否在数组中
>>> apple=1 >>> banana=2 >>> zero=0 >>> apple and banana 2 >>> banana and apple 1 >>> apple and zero 0 >>> apple==banana False >>> apple is not banana True >>> banana or apple 2
and返回最后一个真值，or返回第一个真值。顺便加了个身份操作符的练习（判断false和true）
>>> x=2
>>> if x==2:
... print("you are very good")
...
you are very good
先给x赋个值，然后进入if语句
>>> x=3
>>> y=4
>>> if x is y:
... print("x is y")
... elif x!=y:
... print("you are very good")
... else:
... print("what is you doing")
...
you are very good
if判断true和false来执行后续语句
