The understanding and application of NULL without none True in Python

How do you often see these situations when you're making a judgment on python?

If True:

If s:

If key is not None:

If not s:

And so on that judgment

Understand

1 NULL is a data type of without as

S= "

L=[]

D = {}

t = ()

All of these represent no elements

In [Sat]: s= ' in []: ' If s: ....: print ' s string not empty ' ....: ' Else: ....: print ' s string is empty ' ....: s string is empty

Often, judging whether a string has a ' out of space ' or ' \ n ' element is commonly judged as follows

If S.strip (): Passelse:pass

2 None Type

None is a nonetype type, note is type

in [[]: A = Nonein []: Type (a) out[49]: Nonetypein [[]: Type (None) out[50]: Nonetype

in [+]: If A is not none: ....: print ' A not none ' ...: Else: ...: print ' None ' ....: none

Commonly used to determine whether an element is of type none

If A is not None:passelse:pass

None often appears in the default parameter assignment of the function Def f (s=none) and return value in the None

3 Boolean type True False

In [the]: if True: ....: print ' true ' ....: ' Else ' ...: print ' false ' ....: true

Common: return True of a function or if judgment

If True equals if not False

in [+]: not falseout[47]: True

4 Not for negate

Note that the counter can not be used!

If not s:

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The understanding and application of NULL without none True in Python