Python's function of learning notes

Function

Functional programming The most important thing is to enhance the reusability and readability of code

1. Define and use

def function name (parameter):

...

function body

...

return value

The definition of a function has the following main points:

def: A keyword that represents a function

Function name: the names of functions, which are called later by function name

Function Body: A series of logical computations in a function

Parameters: Providing data for the function body

Return value: When the function is finished, you can return the data to the caller

Example:

1 def Mail (): 2     n = 1233     n + = 14     print(n)5Mail ()6 F = Mail7 F ()

Results:

124

124

1-1 return value

A function is a function block that executes successfully or is required to inform the caller by the return value .

1 def Show (): 2     Print ('a') 3     return [11,22] 4     Print ('b') 5 Show ()

Results:

A

1-2 parameters

There are three different parameters in the function:

• General parameters
• Default parameters
• Dynamic parameters

General parameters

1 def Show (A1,A2): 2     Print (A1,A2) 3 4 Show (11,22)

Results:

11 22

default parameter: The default parameter needs to be placed at the end of the parameter list

1 def Show (a1,a2=99):2     print(a1,a2)34 Show (11)

Results:

11 99

Specifying parameters

1 def Show (A1,A2): 2     Print (A1,A2) 3 4 Show (a2=123,a1=190)

Results:

190 123

Dynamic parameters

1 def Show (*arg):#  *-Receive parameters and convert tuples 2     print(Arg,type (ARG))  34 Show (1,56,78,8979)

Results:

(1,56,78,8979) <class ' tuple ' >

1 def #   * *-Receive parameters and convert     dictionary 2     print(Arg,type (ARG))34 Show (n1=78,uu=123)

Results:

{' UU ': 123, ' N1 ': <class ' dict ' >

1 def Show (*arg1,**args):#  one * in front, two * in the rear 2     print(Arg1,type (ARG1) )3     print(Args,type (args))45 Show (12,34,34,54,n9= 33,n2=99)#  A * in front, two * in the back

Results:

(<class, si, si) ' tuple ' >

{' N2 ': N9 ': <class ' dict ' >

1 defShow (*arg1,**args):#A * In the front, two * in the back2     Print(Arg1,type (arg1))3     Print(Args,type (args))4 5L = (11,22,3,4)6D = {'N1': 89,'K1':'Hello'}7Show (L,D)

Results:

((One, 3, 4), {' K1 ': ' Hello ', ' N1 ':] <class ' tuple ' >

{} <class ' dict ' >

Obviously, the results are not what we want . The point is if we use Show (L,D)

So there's no difference between using show (1,56,78,8979). Therefore, in order to solve this conflict problem , only need to add a *in front of the D , plus two * in advance * can:

1 defShow (*arg1,**args):#A * In the front, two * in the back2     Print(Arg1,type (arg1))3     Print(Args,type (args))4 5L = (11,22,3,4)6D = {'N1': 89,'K1':'Hello'}7Show (*L,**D)

Results:

(One, 3, 4) <class ' tuple ' >

{' N1 ': ' K1 ': ' Hello '} <class ' Dict ' >

To meet our requirements .

Dynamic parameter implementation of string formatting:

1 " {0} is {1}"2 ret = S1.format ('young','  Handsome')3print(ret)

Results:

Young is handsome

1 " {0} is {1}'2 l = ['young','handsome2'  ]3 ret = S1.format (*l)4print(ret)

Results:

Young is handsome2

1S1 ='{Name} is {value}'#Dictionary here is not {0}, {1}, but with {key}, {value}2ret = S1.format (name=' Young', value='Handsome')3 Print('First:', ret)4 5S2 ='{name2} is {key}'6D = {'name2':' Young','Key':'Smart'}7RET = S2.format (* *d)8 Print('Second:', ret)

Results:

First: Young is handsome

Second: Young is smart

2. built-in functions

any: As long as one is true , it is true.

Ord and chr used together

Chr Ord Random.randint can produce verification codes

Enumerate

Eval

Map

Filter

1 li=[1,22,33,45,74,788]2def  func (num):3     if num>33:4         return  True5     Else : 6         return False 7 n = filter (func,li)8Print(list (n))

Results:

[45, 74, 788]

take out the elements in the list that are greater than

Python's function of learning notes