Python parameter type

http://cage.8cuo.org/?p=115

Python's parameter types can be grouped into 4 categories: 1. Position parameters 2. keyword parameter 3. Tuple parameters 4. Dictionary parameters
First, Position parameters:
Features: Unlimited number of calls must provide the number and position are the same as the formal parameters of the argument;
Sample code:
#函数声明
#第三个参数要能转化为数字, or the error will be
DEF fn (a,b,c):
sum = a + B + C
num = int (c);
#函数调用
FN (1,2,3) #正确的调用
fn (1) #错误的调用
fn (1,2, ' ASD ') #错误的调用

Second, keyword parameters
Features: Unlimited number, no need to care about the order of parameters, when the corresponding parameter is not passed, there is a default value for the function to use.
Sample code:
#函数声明
DEF fn (A = 1,b = 2, c = 0):
Print a
Print B
Print C
#函数调用
FN () #正确, a = 1, b = 2, c= 3
FN (10,11,12) #正确, a = ten, B = one, c = 12
fn (10,b =, c =) #正确, a = ten, B = c= 30
fn (10,c =, B = #正确, a = 10,b = 21
fn (c = 2, B = 4, a = 7) #正确, a = 7, B = 4, c = 2
fn (A = 2l, C =8) #错误, the first argument passed by the function does not use a keyword. The default is passed to the first formal parameter of the function declaration. A value is passed again to the keyword parameter A, which triggers Python's typeerror:multiple values for keyword argument ' a ', that is, the keyword parameter A has more than one value
fn (A = 12,1,4) #错误, the keyword parameter, whether declared or called, should be after the position parameter

Three, tuple parameters
Features: The number of parameters is not fixed (call is not required to know the need to pass a few parameters), the number of arguments can be 0, can also be countless.
Sample code:
#函数声明
DEF fn (*args):
For i in args:
Print I
#函数调用
FN (1,2,3) #正确, printed separately 1,2,3
FN (* (1,2,3)) #正确, print out 1,2,3
Note: When the parameter of a function has a * flag, Python handles the incoming arguments internally, i.e. converting the obtained arguments to a tuple (tuple). For the first call in the example above, there are two steps to understand:
Step1: The function received three arguments 1,2,3
Step2: Use these 3 arguments to form a tuple
In the second call, the parameter received by the function is itself a tuple, but the call is to prefix the actual participation of the tuple type to indicate that this is a tuple parameter

Four, dictionary parameters
Features: Similar to tuple parameters, but unlike tuple parameters, dictionary parameters are equivalent to an unfixed keyword parameter, which is equivalent to an indefinite number of positional parameters.
Sample code:
#函数声明
DEF fn (**keyargs):
For k,v in Keyargs.items ():
Print K + "=>" + V
#函数调用
fn (A = 2, B = 3, c = 4) #正确, print out a => 2,b = > 3, c => 4
fn (**{' a ': 2, ' B ': 3, ' C ': 4}) #正确, print out a => 2,b = > 3, c => 4
Description: Similar to the tuple parameter, the function will receive the parameter in the form of key => value to form a dictionary for use within the function
The last thing to note:
When several types of parameters are mixed, note the order in which they are written, in the correct order:
Positional parameter-keyword parameter-tuple or dictionary parameter