python determine whether a list dictionary string tuple exists a certain value or null value (multiple methods)

Determine if a value exists

The almighty in vs. not in:
In strings, lists, tuples, and dictionaries, you can use in and not in to determine whether a value exists.
String:

>>> a='baidu'
>>> 'ba' in a
True
>>> 'ab' in a
False

List:

>>> b=['baidu','taobao','jingdong',3]
>>> 3 in b
True
>>> 'taobar' in b
False

Tuple:

>>> c=('taobao','jingdong')
>>> 'taobao' in c
True
>>> 'tatao' in c
False

Dictionary:
If you don't add keys or values, just compare key

>>> d={'taobao':12,'jingdong':23}
>>> 'taobao' in d
True
>>> 12 in d
False
>>> 12 in ()
False
>>> 12 in ()
True

In python2 you can also use the has_key method

>>> d.has_key('taobao')
True
>>> d.has_key('taob3')
False

Determine if the value is null

Method I:
In Python, False,0,'',[],{},() are all false, so you can perform logical operations directly. It is recommended to use this method for better performance.
For example:

a=[]
if a:
	print 22
else:
	print 33
> if d['jingdong']:
...     print 22
...
22

Method II:
You can use the function len() to compare.

>>> len(a)
0
>>> a=''
>>> b=[]
>>> len(a)
0
>>> len(b)
0
>>> e={}
>>> len(e)
0

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