Let's explain a few concepts here.
-Position parameter: An argument set by position that implicitly saves the corresponding parameter with a tuple. Most of the time we use is by position. For example, there is a function def func (A,B,C), which calls Func (1,2,3). That is a=1,b=2,c=3
-Keyword parameters: You can set parameters through the keyword, do not care about the parameter position, implicit in the dictionary to save the formal parameters. For example, there is a function def func (a,b,c), called Func (b=1,c=2,a=3), that is, a=3,b=1,c=2
Normal format
Copy Code code as follows:
def func (Opt_args):
...
return value
functions with collection of positional parameters
Format is as follows
Copy Code code as follows:
def func (*params):
...
return value
Usage
When you use a function, instead of restricting the number of arguments, *params automatically collects incoming arguments as a tuple.
Instance
Copy Code code as follows:
def func (*params):
Print params
A = [1,2,3,4]
b = ' Hello '
c = 3
Func (A, B, c)
Output
Copy Code code as follows:
([1, 2, 3, 4], ' Hello ', 3)
Functions with collection of keyword parameters
Format is as follows
Copy Code code as follows:
def func (**params):
...
return value
Usage
**params automatically collects incoming parameters as a dictionary when a keyword is passed.
Instance
Copy Code code as follows:
def func (**params):
Print params
Func (A=1, b=2, c=3)
Output
Copy Code code as follows:
{' A ': 1, ' C ': 3, ' B ': 2}
Function Special Usage
Default parameters
Format
Copy Code code as follows:
The equal sign (=) number is the default, and you can call the function without having to pass the parameter to the default.
Instance
Copy Code code as follows:
def func (a = 1, b = 2):
Print A, b
Func (A=3)
Output
Copy Code code as follows:
function can return multiple values
Format
Copy Code code as follows:
Instance
Copy Code code as follows:
def func (a = 1, b = 2):
Return A, B
Print func (a=3)
Output
Copy Code code as follows:
inline functions and closures
Format
Copy Code code as follows:
def foo () #外部函数
def bar () #内嵌函数
....
....
If the inline function references a variable of an external function (including external function arguments), the variable referred to is called a free variable, then the inline function is called a closure. Let's look at the professional explanation: Closure (Closure) is the abbreviation of lexical closure (lexical Closure), is a function that references a free variable. The referenced free variable will exist with this function, even if it has left the environment that created it.
Instance
Copy Code code as follows:
def foo (A, B):
x = 4
def bar ():
return x * a + B;
Return bar
f1= foo (1, 2)
f2= foo (2, 3)
Print F1 (), F2 ()
Output
Copy Code code as follows:
transfer Function
Python everything is object, function This grammatical structure is also an object, you can pass the function name as a parameter
Format
Copy Code code as follows:
def bar (*param1, **param2):
....
def foo (bar, *param1, **param2):
Bar (*param1, **param2)
Instance
Copy Code code as follows:
def bar (*param1, **param2):
Print param1
Print param2
def foo (bar, *param1, **param2):
Bar (*param1, **param2)
Foo (bar, 1, 2, 3, a =, B = 222, c = 333)
Output
Copy Code code as follows:
(1, 2, 3)
{' A ':, ' C ': 333, ' B ': 222}
anonymous functions and lambda
The lambda syntax can create an anonymous function, which is mainly about simplifying writing and is a syntactic sugar.
-Format
Copy Code code as follows:
Lambda [arg1[, arg2, ... argn]]: expression
Instance
Copy Code code as follows:
def foo (x, y):
return x + y
print "Call foo function, result is:", foo (3, 4)
Bar = lambda x = 2, y = 3:x + y
Print "Call lambda fucntion, result is:", bar (3,4)
Output
Copy Code code as follows:
Call foo function, result is:7
Call Lambda fucntion, result is:7
